EPA-600/4-77-045
November 1977
Environmental Monitoring Series
VERTICAL FLUXES AND EXCHANGE
COEFFICIENTS IN THE AIR OVER ST. LOUIS
Field Program 1975
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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VERTICAL FLUXES AND EXCHANGE COEFFICIENTS
IN THE AIR OVER ST. LOUIS
Field Program 1975
by
Bernice Ackerman
Illinois State Water Survey
Urbana, Illinois 61801
Grant Number: R803682
Project Officer
James L. McElroy
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products constitute endorsement
or recommendation for use.
ii
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ABSTRACT
A field program was carried out in the greater metropolitan area of
St. Louis, Missouri during February and July of 1975 as part of the
Regional Air Pollution Study (RAPS). The purpose of the program was to
collect atmospheric measurements needed for future studies of the planetary
boundary layer (PEL) over urban and industrial areas and surrounding rural
areas. The overall goals of the PEL study are to (1) describe the thermo-
dynamic, wind and turbulence fields over the region; (2) determine the
magnitude and vertical variation of the vertical fluxes of heat, moisture
and momentum as a function of land use; (3) obtain estimates of the
exchange coefficients of these variables; and (4) determine the dependence
of turbulence intensity on land use.
Three measurement systems were used: 1) a network of double-theodolite
pilot-balloon stations; 2) two tethered-balloon sounding stations; and
3) an aircraft instrumented for air motion measurements. The pilot-balloon
stations provided simultaneous measurements of the wind profile with
vertical resolution of about 50 m up to 2 km from five or six locations
in the area. The tethered-balloon sounding systems yielded thermodynamic
and wind profiles, with vertical resolution of 20 m from surface to about
500 meters. The instrumented airplane provided measurements of the three
components of wind velocity and of high frequency fluctuations in velocity,
temperature and humidity.
The observational periods were scheduled for 3 or 4 hour durations
during field experiments, or missions, in which all available measurement
systems were operated in modes to best attack particular experimental
objectives. The mission objectives served the overall goals listed above.
They were (a) mapping missions to delineate the thermodynamic, wind and
turbulent fields over the region, (b) flux missions to provide estimates
of the true vertical fluxes of momentum, heat and moisture simultaneously
with vertical profiles of these variables, and (c) nocturnal missions to
provide information on the strength of the nocturnal heat island circu-
lation.
About 1000 wind profiles were obtained from the pibal wind measuring
network, and the tethered-balloon systems yielded over 200 good thermo-
dynamic and wind profiles. One hundred hours of scientific data were
collected during 25 flights with the instrumented airplane. All of these
data have been processed and are stored on magnetic tape for further
processing and computer analysis.
111
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This report was submitted in fulfillment of Grant Number EPA 803682
by the Illinois State Water Survey under the sponsorship of the U.S.
Environmental Protection Agency. This report covers the period February 1,
1975 to November 15, 1976 and work was completed under this grant as of
December 20, 1976.
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CONTENTS
Abstract iii
Figures vii
Tables ix
Acknowledgements x
\. Introduction 1
Background 1
Objectives 2
2. Facilities 4
Aircraft 4
Pilot balloon measurements 8
Tethered balloons: Boundary layer profilers 11
Operations base 14
3. Operations summary 15
General field procedures 15
February program 18
July program 18
4. Data summary 21
Aircraft data 21
Pilot balloon wind measurements 21
Boundary layer profiler measurements 25
Status of data reduction 26
5. Data Sample and Research Projections 27
Nocturnal Observations July 26-27, 1975 27
Nocturnal Observations July 25-26, 1975 36
Summary 38
References 41
Appendices
A. Availability of data: boundary layer profiles 42
B. An investigation of the errors in estimating wind
velocity by double-theodolite pilot-balloon observations....47
Introduction 47
Test procedures 49
Error analysis 49
Error in wind direction 51
Error in wind speed 51
Vector error 56
v
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CONTENTS
Error in calculated balloon ascent rate 56
Error in balloon height 58
Discussion 58
References 60
C. Illinois State Water Survey Data Policy , 61
vi
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FIGURES
Number Page
1. Photographs of the airplane and instruments 6
2. Map showing location of observing sites , 9
3. Photographs of boundary layer profiler and sensors 13
4. Typical flight patterns 16
5. Root-mean-square errors in the pibal measurements 24
6. Average wind speed and direction during special tests of the
pibal systems 24
7. Time-height analyses of temperature at the two profiler stations
and of the urban-rural temperature difference on the night of
July 26-27 29
8. Simultaneous temperature profiles at downtown city and rural
stations 30
9. Time-height analyses of mixing ratio at the two profiler stations
and of the urban-rural difference on the night of July 26-27 31
10. Time-height analyses of the wind speeds and direction, from
double theodolite observations on the night of July 26-27 32
11. Time-height analyses of wind speed at the two profiler stations
on the night of July 26-27 35
12. Time-height analyses of temperature at the two profiler stations
and of the urban-rural temperature differences on the night of
July 25-26 37
13. Time-height analyses of mixing ratio at the two profiler stations
and of the urban-rural difference on the night of July 25-26 39
14. Time-height analyses of wind speed at the two profiler stations on
the night of July 25-26 40
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FIGURES
A-l. Locations of observing stations 46
B-l. Mini-networks used in tests of accuracy of the double theodolite
pibal systems 50
B-2. Profiles of average wind direction on three test days 52
B-3. Profiles of average wind speed on three test days 53
B-4. Profiles of estimated error in wind direction, for each test
day 54
B-5. Profiles of estimated error in wind speed and the vector error in
wind velocity for each test day 55
B-6. Profiles of average balloon ascent rate and of estimated error in
ascent rate for each test day 57
B-7. Profiled of estimated error in balloon height estimated for each
test day 59
viii
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TABLES
Number Page
1. Pilot balloon stations 10
2. Boundary layer profiler sensor characteristics 12
3. February operations 18
4. July operations 20
A-l. Pilot balloon measurements available for February 1975 43
A-2. Pilot balloon measurements available for July 1975 44
A-3. Availability of data from boundary layer profilers 45
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ACKNOWLEDGMENTS
A field program the size of that carried out during 1975 can be
successful only through the dedicated efforts of many people. The
contributions of the many who assisted in this program and in the massive
processing task are gratefully acknowledged.
Mr. J. William Mansell supervised the field operations of the pilot
balloon component and, with the able assistance of Mrs. Yueh Liu, the data
reduction. The field observations were made by the 5th Weather Squadron
the Air Weather Service, U. S. Air Force under the supervision of M. Sgt.
Lewis Jones in February and of M. Sgt. Joe Markham in July. There would,
of course, be no data without the efforts of the 20 enlisted observers who
spent so many hours driving through St. Louis traffic and peering through
theodolite telescopes.
Mr. Gregory Fetter and Mr. Gregory Dzurisin operated the Boundary
Layer Profilers during the July program and Dr. Peter H. Hildebrand
supervised the development of the computer processor and of the data
reduction of these measurements. Mr. R. B. McBeth and his colleagues at
the Field Observing Facility of NCAR provided invaluable cooperation in
providing immediate assistance in the frequent repair of the profiler
sensor packages.
NCAR pilots, Mr. Tom McQuade and Mr. Clay Orum, masterfully guided the
airplane through the tall towers, aircraft and deep-blue haze of the St.
Louis boundary layer, while maintaining good relations and cooperation with
the FAA controllers at the St. Louis control tower, who were most helpful
in working the air operation into their heavy work schedule. Mr. Richard
Friesen, NCAR technician, kept the complicated scientific package running
with a minimum of down time.
The personnel of the Creve Coeur offices of RAPS were extremely
helpful during both the pre-program installations and the data collection.
It would be difficult to name all those who provided assistance at one time
or another, but the cooperation of Frank Schiermeier was an important key
to the success of this effort.
Credit for the success of this program must go to all of these people
and to many others back at the various home facilities who pitched in to
respond to emergency calls. Most of all the professionalism and the most
willing and good-natured cooperation of all under the fatiguing and
stressful conditions of a concentrated field program was greatly
appreciated.
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SECTION 1
INTRODUCTION
BACKGROUND
The dispersion of surface-generated materials and gases in the lower
atmosphere is determined by transport with the mean wind and by spreading
due to small-scale turbulence. The direction of the mean wind determines
the general orientation of_ the pollutant transport, whereas the pollutant
concentration is a function of the variability of the wind, the small scale
turbulence, and the mechanically and convectively driven vertical currents.
Urban pollutant dispersion models have proliferated over the past few
years. A few are relatively simple but many have very elaborate source
distributions in space and time. Virtually all have a major weakness —
the simplicity of the atmospheric module, which frequently consists of a
single wind measurement and simple diffusion parameters. Applications of
these models usually use estimates of the air motion from the surface
boundary layer and from a single urban or rural site. However both the
mean and turbulent components of the wind vary with height and with the
character of the underlying surface and pollutant concentration is strongly
affected by the wind structure throughout the atmospheric boundary layer
over-riding the area of interest.
The simplicity of the atmospheric modules in most models stems from
lack of information, not from lack of importance. Both the mean and
turbulent components of the regional wind field in the lower atmosphere
must be considered in models predicting regional air quality or regional
climate. This is particularly true in the case of metropolitan areas since
the physical structure of cities and the concentration of human activities
may cause systematic differences in the structure of the planetary boundary
layer, and thus in the wind distributions over urban and surrounding rural
terrains.
The mean winds are expected to change in the vicinity of a city,
first, because differences in the surface roughnesses of urban and rural
terrains modify the frictional force and, secondly, because distortion in
pressure surfaces arising from differences in the thermal characteristics
of urban and rural surfaces causes local modification of the pressure
gradient force. The magnitude and characteristic of the turbulent
component of the air motion is also expected to vary over a region
including an urban complex. The mechanical turbulence should vary because
of the differences in the nature, size and number of the roughness
elements, and the convective turbulence because of urban-rural differences
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in the low-level static stability stemming from surface temperature
differences.
There have been reports of observations which indicate that the mean
winds do indeed change as the air approaches and passes over a metropolitan
area, both at the surface (Chandler, 1960; Findlay and Hirt, 1969), and
some distance into the planetary boundary layer (Angell et al., 1971, 1973;
Acis3rman, 1972, 1974a, b; Hass, et al., 1967). There have been very few
observations of the turbulence in air passing from rural to urban sites,
but the work by Bowne and Ball (1970) indicates that there are significant
urban-rural differences in turbulence intensity. Beyond some "plume"
studies, virtually nothing is known of the magnitudes of the vertical
fluxes and flux divergences — yet these are critically important in
determining the depth of mixing, the dilution, and large-scale transport of
pollutants.
All in all, knowledge is fragmentary and there continues to be a great
need for detailed documentation and description of the three-dimensional
airflow in the planetary boundary layer over a metropolitan area, if it is
to be adequately treated in urban dispersion models. The following
sections of this report describe a field program which was designed to
collect the data needed to develop such a description. The program was
carried out in the St. Louis metropolitan area in 1975 in conjunction with
the Regional Air Pollution Study (RAPS) and the Metropolitan Meteorological
Experiment (METROMEX).
OBJECTIVES OF THE STUDY
The research carried out under this grant is part of an urban boundary
layer program which seeks to describe in detail the three-dimensional wind
field in the planetary boundary layer over-riding a mesoscale region which
includes an urbanized area. This program was initiated in 1971 as part of
METROMEX and has continued since then, becoming part of the RAPS program
also in 1975. It has been supported over the years by the National Science
Foundation (NSF), the Atomic Energy Commission (AEC), the Energy Research
and Development Administration (ERDA), the National Center for Atmospheric
Research (NCAR), and the United States Air Force (USAF). Under this grant,
the Environmental Protection Agency has provided support for the collection
of boundary layer measurements during the 1975 RAPS winter and summer field
expeditions and for the basic reduction of the data collected.
The overall urban boundary layer program at the Illinois State Water
Survey has the following objectives:
1. Description of the wind, temperature, humidity, and turbulence
fields over the city and surrounding country side and
delineation of the perturbations induced by the city on the
ambient fields.
2. Determination of the vertical fluxes of momentum, heat,
moisture, and aerosols in the Ekman layer, and their variations
with height and land use.
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3. Estimation of the exchange coefficients of the four parameters
given in (2) and their variations with height and land use.
4. Determination of the variations in turbulence intensity and in
the input scales with land use.
The field efforts of this 1975 project addressed all of these
objectives, with particular emphasis on the second and third. They were
implemented during the periods of 15 through 28 February and 1 through 30
July so as to study conditions in both winter and summer.
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SECTION 2
FACILITIES
Observations were made with three measurement systems: a network of
double theodolite pilot balloon stations, an aircraft instrumented for
measurements of air motion, and (during July only) two tethered balloon
sounding stations. Supplementary routine measurements are available from
the EPA/RAPS radiosonde and tower networks, from the Illinois State Water
Survey METROMEX surface networks and from the St. Louis Air Pollution
Control and Illinois EPA networks. During some experimental periods
additional data are available from other RAPS and METROMEX field
experiments,
AIRCRAFT
An instrumented aircraft, pilot, and technician were provided by the
Research Aviation Facility of NCAR. In February the airplane was based at
Lambert Field; in July it was based at Alton Civic Memorial Airport,
Illinois.
The airplane was the Queenair 306 which was instrumented to provide
measurements of three components of wind velocity and high frequency
fluctuations in velocity, temperature and humidity, as well as standard
state parameters and aircraft position. Equipment to measure concentration
of total condensation nuclei, obtained on loan from EPA-Las Vegas,' was
added during the July program.
Measurements of the turbulent or fluctuating components of the
atmospheric structure were obtained using rapidly responding instruments,
most of which were mounted on a boom extending about 3 meters out in front
of the aircraft. The remaining instruments were either wing- or
fusilage-mounted.
The airplane instrumentation permitted measurement of the following
atmospheric, surface, and aircraft parameters:
1. Air Temperature
a. Slow response (a few seconds) — NCAR reverse-flow
thermometer.
b. Medium response (a few tenths of a second) — Rosemount
platinum resistance thermometer.
c. Fast response (a few hundredths of a second), fluctuations
only — NCAR "K-probe", platinum resistance thermometer.
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2. Dew-point temperature (slow response — about 2 seconds),
Cambridge dew-point hygrometer.
3. Atmospheric refractive index (response, a few hundredths of a
second). NCAR microwave refractometer.
4. Cloud liquid water content — Johnson-Williams liquid water
content meter.
5. Concentration of condensation nuclei (July only) -- Environment I
nuclei counter.
6. Surface Characteristics
a. Radiation-temperature (analog IR), Barnes PRT-5.
b. Visual, aerial color photography — downward-viewing time
lapse movies, 4 sec/frame.
7. Altitude
a. Static pressure probe (transducer).
b. Geometric altitude above ground (for altitudes of less
than one kilometer only) -- Radio altimeter.
8. Airspeed (dynamic pressure)
a. Wing-mounted Rosemount pitot.
b. Boom-mounted pitot and transducer.
9. Orientation to airstream (boom-mounted)
a. Angle of attack, fixed vane.
b. Angle of attack, rotating vane.
c. Sideslip angle, fixed vane.
10. Boom accelerations — vertical and lateral accelerometers,
boom-mounted.
11. Orientation to fixed system, aircraft attidude angles, pitch,
roll, and yaw.
12. Aircraft velocity relative to ground — Inertial Navigational
System (INS)
a. Heading
b. Ground speed
c. Vertical velocity
d. Vertical acceleration
13. Aircraft position
a. INS-computed latitude and longitude.
b. Distance to several DME stations (July only).
In Figure 1 are photographs of the airplane and externally-mounted sensors
or sensor housings.
All measurements (except the aerial photography of course) were
recorded on magnetic tape. All analog outputs were recorded at 16 times
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i
!~
I
GUST
jPROBE
MICROWAVE
.REFRACTOMETER
WING-MOUNTED
INSTRUMENTS
FIXED VANE:
angle of attack
ROTATING VANE:
angle of attack
DYNAMIC
PRESSURE
IFAST RESPONSE
THERMOMETER
MICROWAVE
REFRACTOMETER
PITOT
(dynamic
pressure)
THERMOMETER
LIQUID WATER
CONTENT METER
REVERSE FLOW
THERMOMETER
c d
Figure 1. (a) The NCAR Queenair 306 instrumented to collect air motion measurements. (b) Closeup of
the gust probe. (c) Closeup of the micro-wave refractometer. (d) Closeup of wing-mounted instruments.
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per second; digital outputs (e,g, from the INS) were recorded at 8 or 10
times per sec. Some of the basic instruments were fitted with electronic
filters having 4 Hz bandwidth. During the basic processing, which was
provided by NCAR, all measurements were brought to a common rate and
frequency response through a series of cubic interpolations and application
of a "matching" digital filter. The "standard rate" processed data
provided by NCAR on magnetic tape were recorded 8 times per second, and
1-second (8 point) averages at a one second rate. However, all data have
been filtered so that the measurements contain information only for
frequencies of 4 Hz or lower.
The fast response boom-mounted dynamic pressure and temperature, and
refractometer measurements were also recorded, before electronic filtering
at high rates of 256, 128, and 64 times per second, respectively. These
data were scaled and recorded, without any digital filtering, at the
original rates. This permits study of the fluctuations in total air
motion, temperature and humidity in the high frequency domain.
Some of the parameters to be analyzed were measured directly; others
were calculated from the measurements from several sensors. The parameters
required for the study are listed below. The numbers in parentheses refer
to the basic measurements listed above which enter into their calculation.
a. Aircraft position, in the horizontal, by integration of
measurements from (12), with update from (6b) and (13b)
when available; height from (7b) below 900 m and
calculated pressure altitude from (7a) at all altitudes.
b. Surface characteristics and land use — qualitative (6b).
c. Surface temperature — computed from (6a) assuming black
body radiation.
d. *Absolute air temperature (Ib), with (la) as backup.
e. *Absolute air humidity (2).
f. Pressure changes (spatial) below 900 m AGL: D-values
computed from (7a) and (7b).
g. Turbulence intensity: (8b).
h. Temperature fluctuations: (Ic) and (Ib).
i. Humidity fluctuations — computed from (3), (Ic), (7a),
(8b).
j. Wind components, u, v, w, computed from (11), (12), (8a),
or (8b), (9a or b), (9c), with corrections based on (7a),
(10).
k. Turbulent fluxes of momentum, heat, and moisture, based on
auto-correlations of derived parameters (h), (i), and (j)
above.
1, Spectra and co-spectra of fluctuations in total wind,
temperature, humidity, and vertical wind component, based
on derived parameters (h), (i), (j) listed above and from
(8b).
* Absolute used here in sense of "mean" value, as opposed to fluctuating
component.
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PILOT-BALLOON MEASUREMENTS
Wind measurements were obtained up to about 2000 m using
double-theodolite techniques. These involve tracking a pilot balloon
(pibal) with theodolites from two well-separated locations.
The personnel required to make these observations were provided by the
Air Weather Service (AWS) of the U. S. Air Force from the 6th Weather
Squadron (Mobile). During February the AWS unit consisted of 6 two-man
double theodolite teams plus two supervisors. During July, only 5 two-man
teams and one supervisor were available for this assignment. Standard
equipment required for the observations plus the vehicles necessary to
transport personnel and equipment to observation sites were also provided
by the AWS.
Personnel and the pibal operations center were based at Scott Air
Force Base, Illinois, about 32 km ESE of downtown St. Louis. During each
operational period (see Section 3) the observers were deployed to specified
sites scattered in and around St. Louis. The sites varied from
operation-to-operation depending on the mission for the day. These were
selected from 12 previously surveyed locations (Figure 2).
The 12 pibal sites were established on the basis of a number of
criteria, some scientific, some logistic.
a. Sites should be arrayed such that experiments pertinent to
the objectives could be carried out.
b. The area around each site should have, as much as
possible, homogeneous surface conditions.
c. The baseline (distance between the observers) should be
600 m or longer.
d. The two observers should be able to see each other through
their theodolites, and it should be possible to string
telephone line between them without crossing walks or
heavily traveled roads.
e. There should be no obstructions to the view of the balloon
in any direction.
f. Personal safety of the observers must not be endangered in
any way, and phone and toilet facilities must be within
reasonable walking distance.
g. Equipment could be set up in a reasonable length of time.
h. The site must be within 1-hour driving time from Scott AFB
(an AWS regulation).
i. Permission to use the property from the owner or the
responsible public official must be granted.
It was not always possible to meet all of these criteria. Those which
were essential and had to be met were (a), (d), (f), (h), and (i).
Criterion (c) was met in seven of the sites. The shortest baseline was
about 378 m long, and the longest was nearly 800 m in length. The other
criteria were met with varying degrees of success. The most difficult one
to satisfy was (b), particularly at sites in the city. In fact, even for
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Figure 2. Map of St. Louis showing the location of the pilot balloon sites
(numbered) and the boundary-layer profiler stations (BP1 and BP2).
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criterion (a), the locations, although suitable, were not always optimal.
The locations and baseline lengths of the 12 sites are given in Table 1.
TABLE 1. DOUBLE-THEODOLITE PILOT-BALLOON STATIONS USED
DURING 1975.
Station Baseline
Number Location length (m)
33 East side of main runway, Scott Air Force
Base, IL. 657
35 Troy Road, just south of 1-270, 4 km east
of Glen Carbon, IL. 763
44 South side of parking lot, Korvette Shopping
Center, Rott Road and Hwy. 61, Sunset Hills,
MO. 611
70 Triad High School, Hwy 40, 3 km west of
Hwy. 4, IL. - 449
71 Poag Road, southwest of Poag, IL. 790
72 Brown Road, opposite northeast corner of
Lambert Field, Berkeley, MO. 457
74 Granite City Army Depot, Granite City, IL. 795
75 Army Publication Center, Woodson Road
and Page Ave., Overland, MO. 552
76 County Road, 6 km north of O'Fallon, IL. 640
77 Peabody Road, just west of Hwy. 159, about
8 km south of Belleville, IL. 663
78 Along taxiway north side of Bi-States
Airport, Cahokia, IL. 541
79 Forest Park, along Hwy. 40, east of Hampton
Avenue, St. Louis, MO. 378
When establishing the site, the survey team selected two suitable
spots for the theodolite "pads", requiring that the two be line-of-sight.
They then measured off the straight line distance between the two with
transit and tape and the difference in elevation with a stadia rod. The
orientation of the baseline relative to true north was determined later
from sightings on Polaris on clear nights.
Almost all of the pibal sites were on unprotected public and private
property, so that only small wooden ground stakes marking the theodolite
locations were located permanently at the sites. The observers had to
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transport, set up, and then dismantle all equipment for each day's
observations. This took roughly an hour at both the start and the end of
the day, in addition to travel time.
Two observers, one at each theodolite, composed a pibal "team". They
were linked by a land phone line for communication. Into this line were
hooked a tape recorder and a tone generator that was activated by a timer.
These, along with pertinent electrical connectors were packaged into a
small attache case for convenience of transport and storage. The timing
tone was set for a timing interval of 20 seconds and sounded for roughly 3
seconds. At the start of the tone the observers centered the balloon on
the cross-hairs of the theodolite and kept it there until the tone ended.
Then, before changing the dial settings, each observer, in turn, read the
azimuth and elevation angles of the balloon (to hundredths of a degree)
into their head phones for recording on a cassette tape. Azimuth angles,
as given, were in the coordinate system with y-axis parallel to the
baseline. Rotation of the coordinate system to true north is accomplished
in the data reduction.
Pilot balloons were inflated (to within the accuracy of the gas-flow
meters) for estimated rise rates of about 2.2 to 2.5 meters per second
(mps). Flow meters, rather than weights were used in inflation because of
the short time between the termination of one run and the start of the next
and the difficulty of inflating balloons in the open. Although inflation
rates were assigned, and were adhered to as closely as possible, this was
not an essential factor since the computation of the wind velocity is
independent of the ascent rate of the balloon when double theodolite
measurements are available. In fact, the rise rates are calculated and
provide valuable estimates of the vertical air motions in the boundary
layer.
TETHERED BALLOONS: BOUNDARY LAYER PROFILERS
Two tethered-balloon systems for measuring detailed profiles up to a
nominal operational altitude of 750 m were loaned to the State Water Survey
for the July field effort by the Field Observing Facility of the National
Center for Atmospheric Research. One profiler (BP1) was located at the
RAPS radiosonde station 141 in downtown St. Louis and the second (BP2) at
Triad High School on Highway 40 about 2.5 km west of Highway 4 (Figure 2).
Each balloon system required a senior operator and an assistant. The
operators were State Water Survey staff who were quartered at Collinsville,
Illinois, about midway between the two sites. The assistants were local
area college students.
Details of the system may be found in a paper by Morris et al., 1975.
Briefly, the system consisted of a relatively small plastic balloon
(inflated volume about 3.25 m3) with an aerodynamic shape from which was
suspended the sensor package. The balloon was tethered to the surface and
was raised and lowered using an electric winch in order to obtain
measurements in the vertical.
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TABLE 2, NCAR BOUNDARY LAYER PROFILER SENSORS AND
THEIR CHARACTERISTICS
Variable
Pressure
Temperature
Wet-bulb
temperature
Sensor
Sealed aneroid capsule
Ventilated bead ther-
mister in radiation
shield
Wick-covered thermis-
ter, mounted 2-cm
behind dry temper-
ature sensor
Precision
+1 mb
+0.5°C
+0.5°C
Resolution
0,5 mb
0.1°C
0.1°C
Wind speed 3-cup anemometer,
small, light-weight +.25m/s 0.1 m/s
cups (min. speed:
0.5 m/s)
Wind Magnetic compass,
direction based on assumption +5° 2°
that balloon is effec-
tive vane
The sensor package provided measurements of pressure, dry and wet bulb
temperature, wind speed and wind direction. The sensors and their
precision and resolution are given in Table 2. However, this is a new
system, and these estimates of precision may prove optimistic, particularly
those for the wind measurements. The airborne package also carried a 403
MHz transmitter and circuitry to condition sensor output and modulate the
transmitter. The ground station consisted of a receiver and
Esterline-Angus chart recorder. Photographs of the balloon and sensor
package are shown in Figure 3.
The recording was in a time-multiplex data format with cycling through
8 channels in 20 seconds. As operated during the July field program, dry
and wet bulb temperatures and wind speed were each recorded on two
channels. Thus, these variables were sampled twice every cycle whereas
pressure and wind direction were sampled once. Each channel recorded for
approximately 1.5 second.
The maximum height actually reached by the profiler depended on the
stability and wind speed, decreasing with increasing stability and wind
speed. The balloon was let out at 150-feet per minute and brought back to
the surface at nearly twice that rate. This equipment cannot be operated
under strongly turbulent conditions or in wind speeds of greater than 10
m/sec.
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c d
Figure 3. (a) Boundary layer profiler tethered in parked position. (b) Close-
up of sensor package showing harness by which it was attached to balloon.
(c) Sensor package. The rectangular base box contains electronics and radio
transmitter. (d) End-on view of thermister housing.
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OPERATIONS BASE
The Principal Investigator under this grant directed the day-by-day
operations during both field efforts. She also served as observer and
technician on the airplane.
During the February program, the RAPS offices in Creve Coeur, Missouri
served as a base of operations. Following the RAPS weather briefing,
decisions as to mission operations were relayed to the pibal unit at Scott
Air Force Base and to the pilot at Lambert Field by telephone.
During the July program, the State Water Survey METROMEX base at Alton
Civic Memorial Airport served as base of operations. Facilities included
facsimile weather maps and Service A teletype. Additional weather
information was obtained by phone. Decisions as to the planned operations
were relayed to the RAPS headquarters and to FAA (necessary because of the
profilers) and the three observing components were alerted by telephone.
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SECTION 3
OPERATIONS SUMMARY
GENERAL FIELD PROCEDURES
The operations were usually scheduled as 3- to 4-hour field experi-
ments, or missions, in which all available systems were operated in manners
to best attack particular experimental objectives. The mission objectives
served the overall goals listed in Section 1.
Missions fell into the following general categories:
1. Mapping Mission:
Objective: To map the fields of temperature, moisture, wind,
vertical velocity, turbulence intensity, and vertical fluxes over the
region.
Flight Pattern: "Checkerboard" pattern at one or two levels over
and around the greater St. Louis area, with tracks oriented parallel
and perpendicular to the wind (Figure 4a).
Pilot Balloon Array: Five or six sites activated in as uniform an
areal distribution as feasible. Balloons launched at 20-min
intervals,
2. Flux Cross-Sections:
Objective: To estimate vertical exchange coefficients for
momentum, heat and moisture and their variation with height over urban
and rural surfaces.
Flight Pattern: Two "cross" patterns with arms about 15 to 20 km
long, one parallel and the other perpendicular to the mean wind, One
cross pattern was over a rural area and the other over metropolitan
St. Louis (Figure 4b). During July, the two "crosses" were centered
near the two boundary-layer profiler sites; in February they were near
an urban and a rural pibal site. Traverses were made at three levels,
and the entire pattern repeated at least once.
Pilot Balloon Array: Three sites were activated, two located in
"homogeneous" urban and rural locations (in July at or near the
boundary-layer profiler sites), and the third at a downwind urban
site. Balloons were launched every 10 minutes at the two key sites,
and at 20-minute intervals at the third site.
3. General Cross Section:
Objective: To map, in vertical planes across the city parallel and
perpindicular to the mean wind, the vertical fields of temperature,
moisture, wind, vertical velocity, turbulence intensity, and vertical
fluxes.
Flight Patterns Long traverses extending across the city and well
into surrounding areas, one parallel to the mean wind direction, and
-15-
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Figure 4. Typical flight tracks on (a) mapping missions, (b) flux cross
sections, (c) and (d) general cross sections, and (e) and (f) nocturnal
heat island circulation missions.
-16-
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one or more perpendicular to the wind (Figures 4c and 4d). All tracks
were repeated at three levels, and in some cases the whole pattern
repeated.
Pilot Balloon Array: Five or six sites activated, in a "cross"
array to the extent possible, with one arm parallel and the other
perpendicular to the wind.
4. Nocturnal Circulation:
Objectives^ (a) To check on the existence of the nocturnal urban
heat island circulation and to measure its strength and (b) to check
on the linearity of the wind field which is assumed when calculating
divergence over an area from point measurements, and to evaluate the
error in these divergence estimates.
Flight Patterns: Circuits around the inner city, greater
metropolitan area, and an urban area equal in size to the metropolitan
area, made at two levels and repeated at least once (Figure 4e) or
straight tracks between activated pibal sites which formed triangular
areas (Figure 4f).
Pilot Balloon Array: Five sites activated to form a box around the
metropolitanarea and a triangle over a predominately rural area.
(Optimal array not possible because of limited personnel.)
5. Miscellaneous:
A few special missions were carried out to address particular
objectives which did not necessarily require corrdinated use of all
facilities. These were usually carried out when one or more of the
facility components was not available due to malfunction of equipment
or to unavailability of personnel.
These missions were of two types:
a. Tests and/or checkout of systems.
b. Study of the diurnal evolution of the temperature,
moisture, and humidity profiles or evolution during the
morning and evening transition periods. These utilized
only pibals at two sites and the boundary layer profilers.
On all missions in July the boundary layer profilers were operated in
40-minute sequences, from their permanent sites.
Decision as to mission was made by the Program Director (the Principal
Investigator under this grant) by 9 a.m. each morning on the basis of the
general weather conditions. Following decisions as to timing, flight
pattern and balloon sites to be used in the mission, all units were
notified by telephone as to their particular operations. This had to be
done two to three hours prior to the start of the mission because of the
travel and preparation time required by the various observational
components. Because of this lead time and lack of field communication,
missions could not be changed when late changes in weather forecast or some
equipment failure indicate a modification might be desirable,
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February Program
The winter program was carried out during the last half of February.
The AWS personnel and equipment arrived in the St. Louis area on the 12th
and the NCAR airplane and personnel on the evening of the 15th, Rain fell
nearly continuously between the 12th and 15th, making it impossible to
carry out any operation. However, this time was needed to modify some of
the AWS equipment and to relocate some of the previously located pibal
sites. The pibal sites had been located and surveyed in January and early
February. However, much-above normal precipitation in January and February
resulted in very soft muddy surfaces at some of these locations, rendering
them unworkable.
The weather continued to be considerably less than optimal for the
program during the last half of the month, with predominately low ceilings,
frequent heavy rains and snow, and unusually strong winds on about
one-fourth of the days. Nevertheless nine missions were carried out (Table
3). In one instance last minute failure of a key piece of the scientific
package on the airplane caused cancellation of that part of the mission.
TABLE 3. FEBRUARY 1975 OPERATIONS
Date
2/17
2/19
2/20
Mission
Mapping
Mapping
General cross
Airplane
Time*
(Local)
1345—1745
1135—1440
i i on i A A r
Pibal
Time*
(Local)
1220—1520
1 1 cr> i mn
No. of
Stations
6
£.
section
2/20 Mapping
2/21 Mapping; general
cross section
2/25 General cross
section
2/26 Mapping
2/27*** Mapping
2/28 Flux cross
section
1915—2130
1140—1540 1140—1450
1210—1600 1320—1520
1230—1615 1220—1550**
2045—2358 1210—1510
1325—1650 1230—1520**
3
6
* CST prior to 23 February, CDT 23-28 February
** Pibals on 10-min launch schedule
*** Flight delayed because of equipment malfunction
July Program
The NCAR equipment (airplane and profilers) and personnel arrived in
St. Louis on 30 June. The AWS equipment and personnel arrived late on the
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evening of 2 July. The KCAR units departed on 31 July and the AWS on 1
August. The effective period for full-scale missions was 5 through 30
July. Although a slip of 10 days would have been preferable in order to
fit the dates of the main RAPS expeditions, NCAR scheduling made the
aircraft available to this program only during the month of July,
The approach to the operations was to work the weather, rather than
any set schedule. However, in practice, AWS and NCAR guidelines for their
personnel necessitated scheduling some days-off a day or so in advance.
Although this resulted in the loss of a few good days, the weather was
generally favorable and did not seriously affect the overall data
collection.
There were few failures in the pibal systems and a relatively small
fraction of the scheduled launches were lost because of equipment problems.
Except for an early failure in the inertial navigation system, the
scientific package on the airplane also presented few problems detectable
in the field. However, failures of aircraft equipment did force
cancellation of missions on at least three occasions.
Major equipment failures did occur however in the sensor packages of
the boundary layer profiler systems and occassionally in the recorders.
NCAR had not provided substitute parts, wiring diagrams, or repair
instructions, largely because these were new systems and such things did
not exist. Consequently the sensor packages had to be returned to NCAR in
Boulder each time there was a malfunction. Although repairs were made
immediately and the malfunctioning instrument was back within 36 to 48
hours, there was still nearly a 30% loss in desired profiles.
A total of 25 missions were carried out between the 1 July and 31 July
(Table 4). Three of these were tests or calibration missions.
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TABLE 4. JULY 1975 OPERATIONS
Date
7/01
7/02
7/03
7/05
7/07
7/08
7/09-10
7/10-11
7/12
7/14
7/15
7/16
7/18
7/21
7/22
7/24-25
7/25-26
7/26-27
7/27
7/28
7/29
7/29
7/30
7/31
Mission
Test
Test
Mapping
Mapping
Mapping
Flux cross
section
Nocturnal
Nocturnal
Mapping
Flux cross
section
Flux cross
section
Mapping
P re- rain
mapping
Flux cross
section
Mapping
Nocturnal
Nocturnal
Nocturnal
Mapping
Profile
evolution
Mapping
Flux cross
section &
Profile
evolution
Test
Airplane
Time
(Local)
1510-1627
1420-1806
1255-1700
1218-1550
2133-0010
2132-0025
1300-1700
1250-1627
1319-1705
1142-1435
1106-1457
1230-1620
1247-1702
2133-0020
2100-2230
0010-0130
0300-0425
2116-2342
1300-1450
1350-1525*
1155-1430
* Note airplane flight period
Pibal
Time
(Local)
1100-1400
1320-1640
1230-1530
2140-0020
2140-0020
1340-1620
1310-1610
1310-1610
1200-1500
1120-1420
1320-1620
1320-1620
2130-0010
2120-2400
2140-0020
0600-1500
0600-1500
0920-1145
included
Profilers
No, of Time No. of
Stns. (Local) Stns,
5
5
3
5
5
5
3
3
5
5
3
5
5
5
5
2
2
1
1210-1405
1100-1600
1100-1400
1300-1730
1200-1700
2120-0040
1300-1700
1220-1700
1240-1440
1040-1320
1200-1700
1200-1720
1940-0100
2040-0420
2020-0020
1350-1500
1700-2150
0030-1500
0600-1500
1
2
2
2
2
2
2
2
2
2
2
1
2
2
2
1
1
1
2
in period of pibal and
profiler observations for profile evolution
mission on 7/28
and 2!
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SECTION 4
DATA SUMMARY
AIRCRAFT DATA
Basic processing of the digitally-recorded measurements was done by
the Research Aviation Facility at NCAR. Because of a huge backlog of
flight programs to be processed at NCAR, reduced aircraft data did not
become available to ISWS until late Spring and Summer of 1976.
The reduced data was recorded on magnetic tape as described in Section
2, in a convenient form for further computer processing and analysis.
These tapes contain scaled values (in appropriate units) of parameters 1
through 13 listed in the aircraft section of Section 2. In some instances,
the measurements have been corrected for known performance characteristics
of the instruments (e.g., temperature has been corrected for compressional
heating of the air). In addition position, based on integration of track
information from the navigation equipment, and the three components of the
air velocity were also provided at a rate of once per second.
The voice recordings of observer comments have all been transcribed.
Flight track information has been extracted from the time-lapsed aerial
photographs for three flights of particular interest for use in correcting
the computed tracks. Programs to read the NCAR tapes (generated on the CDC
6600-7600) on the University of Illinois IBM 360 have been written and
others for initial "massaging" of the data are under development. A
program for calculating divergence around closed tracks has been written
and debugged.
Because of the delay in receiving the data and the mass of numbers
involved, it is not possible to estimate the overall quality or the
quantity of useable data at the time of this writing. Review by NCAR
personnel of the processed data and a spot check at ISWS after it was
received, have not indicated any unexpected problems with the basic data.
However during initial exploratory analyses of two flights, timing problems
have been discovered. These arose during generation of computer-compatible
tapes from the air tapes. The problem is easily corrected but does require
reprocessing of parts of the flights by NCAR. This discovery has
precipitated review of all 25 processed tapes, now underway, to detect
errors of this type on other flights.
PILOT BALLOON WIND MEASUREMENTS
The pilot balloon measurements consisted of two sets of azimuth and
elevation angles to the balloon, one from each end of the "baseline".
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These angles, read from the theodolite scales and orally recorded on
cassette recorders, plus the site baseline statistics (length, orientation
relative to true north, and elevation difference in elevation at the two
ends) permit calculation of the average wind for the layer through which
the balloon passes between successive sightings.
The theodolite readings have been computer-processed to obtain winds.
The computations were based on the methods described by Thyer (1962). This
technique solves for location of the shortest distance between the rays
from the two theodolites and estimates the most probable position of the
balloon along the line joining the rays at this location. The minimum
distance between the two rays provides an estimate of the error in the
calculated position of the balloon due to errors in the angles to the
balloon. Thus, the technique provides a means for detecting errors in the
theodolite readings and for correcting them.
The average wind velocity for the layer between two successive reading
times is provided by the difference between the two balloon positions
divided by the difference in the two times. The rate of ascent of the
balloon is determined by the height difference divided by the time
interval.
During the 1975 operations sightings to the balloons were recorded at
20-second intervals, which nominally permits calculation of average wind
velocity for layers of about 50 meter depths. In actuality there was
considerable variation in the depth of the layer covered in the 20 seconds
both because of inaccuracies in the flow meters used to gauge the amount of
gas entering the balloon and because of the frequent existence of
atmospheric vertical currents which provided increments to the ascent rate
of the balloon due to the free lift.
Because of the 20-minute launch interval the balloons were scheduled
for abandonment after 13 minutes of tracking, providing, in still air, wind
data up to about 2 km. Although a fair number of the soundings did go the
full distance, many did not, either because the balloon entered a cloud or
because it passed behind a cloud or surface obstruction.
In Tables A-l and A-2 of Appendix A are tabulated the profiles
obtained during the winter and summer programs. Of the 1068 wind soundings
scheduled, 1000 (94%) were actually made. About half of the missed
soundings were cancelled because of rain. Of the 1000 balloons launched,
739 (74%) were tracked to heights in excess of 1 km by both theodolites.
Computer processing of the 1000 soundings has been completed. They
have been stored on magnetic disk for editing, and further processing.
After editing, the data are archived on magnetic tape, in unformatted
binary code. The tapes contain the following: (a) site information; (b) at
each reading time, the azimuth and elevation angles, height and position of
the balloon relative to the release point, and the "shortest" distance
between the two theodolite rays; (c) calculated wind velocity (u, v,
components and speed, direction), position mid-point in layer (height and
position relative to the Arch), and the rate of rise of the balloon, all
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for the interval between two successive readings. To date 30% of the
soundings have been edited and archived.
The personnel making the pilot balloon observations were trained Air
Force upper-air observers. In addition they were given several days of
special training and practice in the methods used in this program prior to
start of the field expedition. Therefore there is considerable confidence
in the general quality of the data.
Nevertheless the overall accuracy of winds determined from pilot
balloons, even using double theodolite techniques is generally unknown.
The Thyer method permits an estimate of the possible uncertainty in the
angular reading and therefore in balloon position. An analysis of these
estimated uncertainties for a similar wind program in 1971 (Ackerman et al,
1975) indicates that at times they can be sizeable. However, they
represent position errors and are usually systematic so that the errors
largely cancel out when time differentials are taken in the wind
calculations.
In order to try to obtain estimates of the accuracy of the wind
calculations, special experiments were carried out in July 1975, and during
an earlier similar program in 1972. In these experiments several double
theodolite teams set up with parallel baselines, tracked the same balloon
for 6 or 8 launches. Lacking a standard, the average of the individual
measurements may be considered as the best estimate of the true value. The
square root of the pooled variances, which is referred to hereafter as the
root mean square (RMS) deviation, gives an estimate of the error in the
wind measurements. A summary of the results of these experiments are given
below. A detailed description of the experiments and description of the
results are given in Appendix B.
In Figure 5 are shown the profiles of the RMS deviations for wind
speed, wind direction, wind vector, and ascent rate of the balloon, and in
Figure 6 the wind profiles for the three experiments. The RMS deviation in
wind direction was very small — of the order of 2° to 3° up to 1500 m, and
very similar in magnitude in all 3 tests. The RMS deviation in wind speed
was more significant, and unfortunately also varied significantly between
the three experiments, ranging from about 0.2 mps in the most stable case
in 1972 to 0.5 to 2 nps for the 1975 test. The RMS deviations in ascent
rate were far smaller, from 0.1 to 0.2 mps on the most stable day to 0.2 to
about 0.8 mps on July 31, 1975.
A number of factors can contribute to these differences in indicated
errors. Perhaps the over-riding one is the velocity structure itself --
the ease and accuracy with which the balloon can be tracked is directly
related to the turbulence, the wind speed and the variability in direction.
Other factors include the individual measurement "system," in this instance
the personnel and equipment, the angle of the wind to the baseline, and the
distance (range) to the balloon.
All factors were present in this set of tests. The personnel and
equipment were different in 1975 than in 1972 and were not identical even
-23-
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2 3 4
RMS DEVIATION
WIND SPEED (mps)
502 4 6
RMS DEVIATION
WIND DIRECTION (deg)
8 0
2 3 4
RMS VECTOR
DEVIATION (mps)
5 0 0.4 0.8 1.2
RMS DEVIATION
RISE RATE (mps)
Figure 5. Root mean square (RMS) errors for wind speed and direction,
balloon ascent rate and RMS vector error for three field tests.
1.6
1.4
1.2
1.0
0.6
0.4
0.2
1
Aug 9 1972 /
f July 31 1975
y
4 6 8 10 12
AVERAGE WIND SPEED (mps)
- \
July 31 1975
\
Aug 1 1972
Aug 9
14 16 -40 -20 0 20 40 60 80 100
AVERAGE WIND DIRECTION, BASELINE COORDINATES (degrees)
Figure 6. Mean profiles of wind speed and wind direction (in base-
line coordinates) for the durations of the three tests of the double
theodolite system.
-24-
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in the two 1972 experiments. The angle of the wind to the baseline
averaged 50° on August 1972, 42° on August 1, 1972, and 18° on 31 July
1975. The computational technique developed by Thyer is not as sensitive
to "small angle" problems as other methods. However, the fact that the
largest RMS deviation occurred where the crossing angle to the baseline was
largest suggests that even with this method the double theodolite technique
loses some of its advantage when the triangle becomes very obtuse.
For this group of experiments, the crossing angle and the wind speed
appear to be the important elements in determining accuracy. The RMS error
was largest on the day that the crossing angle was smallest. The RMS
deviation was also larger the stronger the wind, increasing from 0.2 or 0.3
raps (less than 5% of the speed) in the lower kilometer on 9 August 1972
when the wind speed was 3 or 4 mps to 0.5 to 2 mps (10 to 20%) on July 31,
1975 when the wind speed was 5 to 9 mps. In addition to increased
difficulty in tracking, strong winds also result in greater range to the
balloon at a given level so that small angular errors, either because of
reading error or because the balloon was not exactly on the crosshairs at
reading time, represent larger (non-systematic) position errors.
BOUNDARY LAYER PROFILER (BLP) MEASUREMENTS
The sensors on the BLP package were interrogated and recorded in
sequence over a 20-second interval. The system used a pen recorder that
provided a chart similar to the standard radiosonde chart. Ten values were
recorded sequentially in each record covering 20 seconds, in the following
order: high reference, low reference, temperature, wet bulb, pressure,
wind speed, temperature, wet bulb, wind speed, wind direction.
The BLP records have been digitized using a digitizer (the Autotrol)
which produces punched IBM cards. All of the useable profiler data have
been processed through a program which scales the input parameters
according to the calibration provided by NCAR and generates, in addition,
the height (using the hypsometric equation), vapor pressure, mixing ratio,
dewpoint, relative humidity, saturation vapor pressures at both dry and wet
bulb temperatures, virtual temperature, potential temperature, and
potential wet bulb temperatures. The vertical "gradient" of potential
temperature, vertical shears in speed and direction, and Richardson number
are calculated for successive readings also but are not very meaningful
because small variations in basic values introduce large variations in
these terms due to the shallowness of the layer over which the dif-
ferentials are taken.
Although the design limit of the balloon and package is 750 m, the
maximum height attained varied as a function of wind speed, turbulence, and
stability. All but 11 exceeded 300 m and nearly half exceeded 500 m.
Both the ascending and descending sections of the soundings have been
processed. The rate of ascent was approximately 45 m/min, the rate of
descent was at least twice that rate. Comparison of the profiles of
temperature and humidity for the two parts of the run indicated that the
descending sections were useable despite the faster rate except for the
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wind speed and direction, and particularly the former. The rapid rate of
descent introduced large error in wind speed and a smaller less significant
error in wind direction.
The performance of the BLP systems was very disappointing. Twenty-six
percent of the scheduled soundings could not be made because of instrument
malfunction or unavailability of sensor backage. Of the 228 soundings that
were made, nearly 20% are unuseable because of instrument malfunction. The
remaining 208 soundings appear to be good, although they have not been
subjected to an in-depth review.
As of this date, all of the profiler data have been processed. In
Table A-3 of Appendix A are tabulated the dates and times for which useable
profiler data are available. These data have been edited for large errors
but require some additional examination for less obvious errors before
incorporation into analyses. Scaled and derived values, and the basic
chart readings are archived on magnetic tape.
Status of Data Reduction
As has been indicated, the basic reduction of the data collected by
each of the facility components has been completed, but only a small
fraction of the data has been edited. The pilot balloon data, when
completely edited, will be available through the RAPS data bank. The
airplane and profiler data will reside at the Illinois State Water Survey.
Data are available to RAPS researchers, subject to the Illinois State Water
Survey data policy (Appendix C).
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SECTION 5
DATA SAMPLE AND RESEARCH PROJECTIONS
The analysis of the data collected under this grant is being funded by
the National Science Foundation*. Because of unfortunate delays and lapses
in funding analysis of the data is barely underway. A study of the
nocturnal heat island circulation, based in part on data collected in the
field program described above, is nearing completion and a report of the
results will be available by midsummer 1977. Currently funded research
covers a study of the turbulent fluxes of heat, moisture and momentum over
urban and rural surfaces. Initial results of this research should become
available by the end of 1977.
One of the case studies carried out in the research on heat island
circulation was based on data obtained on July 26-27, 1975. In the course
of this study, the profiler data were analyzed to determine the temporal
evolution of the nocturnal boundary layer at both the downtown and country
locations (BP1 and BP2, resp, Figure 2). This analysis and a similar one
for the night of July 25-26 are presented below, to illustrate the type of
information contained in this portion of the data bank.
NOCTURNAL OBSERVATIONS, July 26-27, 1975
The weather conditions during the day and evening of July 26 were very
favorable for the development of a significant nocturnal heat island. With
only thin high cloudiness and light winds, the midafternoon temperatures
reached around 30C. The heat island started to increase rapidly around
1400 CDT**, reached its maximum around 2200 and started to decrease very
slowly shortly after midnight.
On the night of July 26-27 observations were made between 2020 and
2320 at the rural station (BP2) and 2100 to 0030 in downtown St. Louis
(BP1). (Instrument problems forced cancellation of some of the scheduled
soundings.) The boundary layer winds were light and from the SSE so that
the two stations were located crosswind with respect to each other.
Moreover the upwind fetches were homogeneous at both locations, urban for
the downtown station and rural for the country station. Thus, the
measurements should be representative of the general locale of the
observing station.
* Grants DES 74-13931 and ATM 76-15870.
**In the following discussion all times are given in Central Daylight Time
(CDT).
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Time-height analyses of temperature at both the urban and rural
profiler stations are shown in Figure 7. At the country station most of the
low-level cooling had already occurred by the time the observations
started, and a strong surface-based inversion existed (Figure 7b). Hie top
of the inversion was quite low, only 100 m above the surface, and increased
only slightly in height (25 m) during the three hours of observation. The
temperature at the top of the inversion also was nearly constant during the
three hours, varying between 24.3 and 24.7C, but with no evidence of a
trend with time. Most of the vertical temperature change (80-90%) occurred
within the first 25 to 50 m above the surface. The region of maximum
temperature at the top of the inversion extended through 50 m at least, and
above that the temperature lapse was roughly neutral.
The situation in the city was quite different, as one would expect
(Figure 7a). The temperature was still high at 2200 and although the rate
of cooling at the surface was not very different than over the rural
surface during the common period of observation, the cooling extended
through a much deeper layer. A surface based isothermal, or very weak
inversion, layer was very shallow (less than 50 m). The main nocturnal
inversion was elevated, and delayed, barely forming by 2130. The base of
the inversion lowered during the observation period from about 175 m to 125
m, while the top remained almost constant in height at 200 to 220 m.
In the city the whole layer from surface to 200 m was stable and
apparently shared in the nocturnal cooling. In the country, on the other
hand, the cooling was concentrated below 100 m. From 2200 on the base of
the elevated inversion in the city lay just about at the height of the top
of the stable layer in the country. The temperature at the top of the
inversion was nearly the same as that at the top of the country inversion,
varying from 23.6 to 24C, but with an indication of an increasing trend
with time.
The urban heat island was very shallow (Figure 7c). The urban
temperature excess dissappeared above 60 m during the part of the night
covered by the observations. A 'negative' heat island (i.e. city cooler
than country) occurred between 75 and 175 m from 2220 on. A comparison of
the temperature profiles (Figure 8) indicates that the reversal in the sign
of the urban-rural temperature difference was related to the fact that the
low-level cooling in the city extended well beyond the top of the country
inversion. Urban-rural equivalency in temperature occurred only above the
urban stable layer.
The nocturnal moisture distributions over country and city sites are
shown in Figure 9. Well mixed conditions existed downtown,.but there was a
significant vertical gradient in the moisture in the lower 50 m of the
rural PEL. Initially this gradient was a lapse, but shortly after 2100 a
moisture inversion developed in the lowest 25 m. A pocket of dry air about
200 m deep appeared late in the evening at both locations, slightly later
and about 100 m higher downtown than in the country. At both locations the
minimum mixing ratio observed was abtrat 9.5 g/kg; however, since it
occurred at the last observing time at both locations, this may not have
been the minimum reached at either one. At both locations this dry pocket
occurred at the top of the nocturnal inversion.
-28-
-------
600
o
o:
CD
o
CO
NJ
<^>
I
500-
400-
300
200
100
JULY 26-27, 1975
TEMPERATURE (°C)
i i i
a. BP 1, DOWNTOWN
22
I i I I
b. BP 2, RURAL (TRIAD H.S.)
24-
2100 2200 2300 0000
1 1 1 \
c. URBAN-RURAL
DIFFERENCE BP 1-BP 2
-°-5
2100 2200 2300 0000
TIME, CDT
2100 2200 2300 0000
Figure 7. Time-height distributions of a) temperature in downtown St. Louis,
b) temperature at Triad High School which is located in a rural setting surrounded
by farmland, and c) temperature difference between the two stations, on the night
July 26-27, 1975. In a) and b) shading indicates inversion or isothermal layers,
and heavy lines the tops of inversions.
-------
w
o
500
400
300
200
100
16
JULY 26 1975
2300 CDT
I
I
17
18
19
20 21
TEMPERATURE, "C
22
23
24
25
Figure 8. Temperature profiles at a station in downtown St. Louis (solid line) and
at a rural station 20 miles to the ENE at 2300 CDT on July 26, 1975.
-------
600
500
S 400
o
oi
CD
o
co
-------
WIND DIRECTION (10 degrees)
WIND SPEED (mps)
o\- SITE 70, July 26-27 1975
26
a.
2120
Rural location
2220 2320
TIME, CDT
0020 2120
2220 2320
TIME, CDT
0020
WIND DIRECTION (10 degrees)
WIND SPEED (mps)
SITE 78, July 26-27 1975
SITE 44, July 26-27 1975
2220 2320
TIME, CDT
0020 2120
2220 2320
TIME, CDT
0020
b. Upwind metropolitan stations
-32-
-------
WIND DIRECTION (10 degrees)
2.2
2.Op SITE 72, July 26-27 1975
1.8 -
SITE 74, July 26-27'1975
2120 2220 2320
TIME, CDT
Downwind metropolitan stations
0020 2120
2220 2320
TIME, CDT
0020
Figure 10. Time-height distributions of wind direction and wind speed
on the night of July 26-27, 1975 as obtained from double theodolite
pibal observations a) at a rural location 25 miles east of St. Louis,
b) at two stations on the south (upwind) side of the metropolitan area,
and c) at two stations on the north (downwind) side of the metropolitan
area. Solid heavy lines indicate maxima in the wind speed profiles
and dashed heavy lines indicate minima.
-33-
-------
The urban-rural differences in mixing ratio (Figure 9c) were negative
(city dry) only in the lowest 50 m. The magnitude of the urban deficit de-
creased with time and by 2300 the near-surface moisture was slightly
greater downtown (by 0.6 g/kg) than in the country. This change was no
doubt due to the loss of moisture from the lowest air layers to the ground
in the country as the surface cooled down and the air became saturated. In
the city, on the other hand, the temperature remained so high that even at
midnight the surface relative humidity was above 60%.
Above the lowest 50 m, the air downtown was more moist than the
country air up to about 200 m (slightly higher later in the evening). This
more moist layer coincided with the layer of relatively cool city air
(Figure 7c), and was probably due to the same cause, namely the deeper
mixed layer over the city.
On clear summer nights with low wind speeds, the wind profiles in the
St. Louis area typically show speed maxima forming in the lowest 200 to 400
m around sunset or shortly thereafter, increasing in magnitude and height
as the evening progresses and frequently splitting into two or three peaks
late in the evening. The evolution of the wind structure, as indicated by
the pibal observations (Figure 10) followed this sequence at all stations.
At the rural location (Figure 10a) the 'jetlet' reached 6 mps while at the
stations on the periphery of the metropolitan area (Figures lOb and c) the
low level speed maxima reached 8 to 10 mps, 2 to 4 mps greater than the
speed minima just above. The levels of these low level jetlets were
generally higher, by several tens of meters, at the two downwind
metropolitan stations (72 and 74) than at the country stations.
The wind was southerly through the lowest several hundred meters on
this night, but at about 800 m it veered sharply from south to west. The
depth of the shear layer was 200 or 300 m early in the night but increased
(and consequently the magnitude of the shear decreased) as the night
progressed. This shear could represent concentration of the shift to
gradient flow to a shallow layer during the afternoon when the mixing
distributed the frictional dissipation of gradient momentum vertically and
the flow to the left of the gradient wind was found through the deeper
layer. This is indicated also by the veering of the wind with time below
the shear layer. This veering occured nearly simultaneously through depth
at the rural and near rural sites (Stations 70 and 78) so that a layer of
near constant wind direction was maintained. At the downwind urban sites,
the isogonal analysis indicates a gradual turning of the wind with height.
The profiler data provides a more detailed look at the structure of
the low-level maximum in wind speed. In Figure 11 are shown the
height-time distributions of wind speed at the two profiler sites, with
greater height exaggeration than in Figure 10 since the profilers provide
much greater height resolution. There was a very strong gradient in wind
speed off the surface in the country (Figure lib), with most of the change
occurring in the lowest 50 to 75m. The low level jetlet was at 200 m at
2050 but dropped rapidly to 125 m and remained between 125 and 175 m.
Shortly after 2200 a secondary maximum formed around 300 m. Both the level
-34-
-------
JULY 26-27, 1975
WIND SPEED (MRS)
I I 1
b. BP 2
RURAL (TRIAD H.S.)
2100 2200 2300 0000
2100 2200 2300 0000
TIME, CDT
Figure 11. Time-height distributions of wind speed on the night
of July 26-27, as measured by boundary layer profilers aj in
downtown St. Louis and b) at Triad High School located in a rural setting
surrounded by farmland. The shaded areas indicate regions of maxima and
the heavy lines the peak values in the vertical profiles.
-35-
-------
and the magnitude of the maximum in the speed profile are in good agreement
with those in the profiles calculated from pibal measurements at the same
location (Figure lOa).
The low level vertical gradient in wind speed was much smaller in the
city than in the country. The surface wind (which was calm in the country)
was about 2 mps downtown. Although there appears to have been some
intermittent formation of maxima below 100 m, the primary maxima occurred
between 200 and 350 m. There was definitely a double structure to the
jetlet from 2130 on, with the lower maximum around 200 m, and the second
about 75 m higher. Both increased in height and speed with time and a
third maximum formed around 225 m again at about midnight. The maximum
speed increased from under 5 mps to a little over 8 mps.
Blakadar (1957) has shown that nocturnal low level jets and nocturnal
inversions are related. This relationship existed on this evening even
though the speed maxima were relatively small. In both the urban and rural
boundary layers, the layers of speed maxima (shaded in Figure 11) occurred
just at the top of the nocturnal inversion (highlighted in Figure 7).
NOCTURNAL EXPERIMENT, July 25-26, 1975
The profiler data have also been examined for the night of July 25-26,
1975. On this night the period of overlapping observations at the two
profiler stations was considerably longer, extending from 2100 on the 25th
to 0400 on the 26th. The low level winds were from the east so that the
upwind fetch at BP2 was rural and air arriving at the downtown site (BP1)
had passed over several miles of urban- industrial surface. Therefore the
measurements were again representative of the locale of the observations.
As will be seen in the following discussion, the boundary layer
structures of all three variables, temperature, moisture and wind, were
very similar to that found on the night of July 26.
Again, a strong surface-based inversion had developed in the country
by 2100 and continued throughout the night (Figure 12b). The stable layer
deepened from about 125 m early in the evening to about 250 m at 0400.
Downtown, the main low-level stable layer was a rather shallow inversion at
around 200 m, lifting about 50 m after midnight (Figure 12a). The base of
the elevated inversion was just above the top of the rural inversion. The
temperatures at the tops of the urban and rural inversion were about the
same.
The urban heat island reached a maximum intensity .of about 8C at the
surface by 2300 and remained within a degree of that for the rest of the
night. The heat island was less than 100 m in depth (Figure 12c). A
reversal in the sign of the urban-rural temperature difference occurred
above the low level heat island, but not until midnight and the negative
heat island did not reach any significant magnitude until nearly 0300. The
layer of the 'negative heat island1 was based at about 100 m, or a little
higher, and increased in depth and magnitude during the early morning
hours. The magnitude of the urban temperature deficit reached a little
-36-
-------
1ULV 25-26, 1975
TEMPERATURE (°C)
/I///I//I/ ////I//
b. BP 2, RURAL (TRIAD H.S.)
I /X//V/A//V/ h / /I///
c. URBAN-RURAL DIFFERENCE, BP 1 - BP 2 '
S-0.2 < At < +0.2
2000
2200
0400
0000 0200
TIME, COT
Figure 12. Time-height distributions of a) temperature in downtown St. Louis,
b) temperature at Triad High School which is located in a rural setting
surrounded by farmland, and c) temperature difference between the two
stations, on the night of July 25-26, 1975. In a) and b) shading indicates
inversion or isothermal layers, and heavy lines the tops of inversions.
-37-
-------
over 1C by the time the observations ended at 0400. As on July 26-27 this
reversal of temperature difference was a consequence of the mixing in the
city and thus a sharing of the surface heat loss through a deeper layer in
the city than in the country.
The urban and rural moisture distributions on the night of July 25-26
(Figure 13) were also similar to those observed on the night of July 26-27.
The lowest 500 m were very well mixed downtown and little change occurred
during the night except for the development of a weak moisture inversion at
around 25 m above ground after 0100. In the country, there was a strong
moisture gradient near the surface and a low level moisture inversion at
about 25 m from 2120 on, which increased in strength as the night wore on.
Whereas the surface mixing ratio remained between 10 and 10.7 gm/kg in the
city it decreased from 11.9 to 9.1 in the country. Thus in the early
morning hours the surface air was more moist downtown than in the country.
Above 50 m, the boundary layer was fairly well mixed at both locations.
A dry pocket appeared about 200 m at both locations on this evening
(slightly later in the city). The minimum mixing ratio was 0.5 g/kg lower
in the city than in the country. This dry pocket could have been due to
advection at both locations although it is unlikely that the air over the
rural site (BP1) could have been the same that appeared downtown in St.
Louis within the hour. Moreover the occurrence of these dry pockets around
midnight on both nights would suggest that they are due to local effects
rather than due to advection.
Between 100 and 200 m the urban moisture deficit decreased with time,
and the urban-rural difference in moisture became positive in the early
morning (Figure 13c). However on this evening the city remained drier than
the country until well after midnight, both at the surface and in this
elevated layer, and the urban moisture excess aloft was quite small.
Low level wind speed maxima also occurred on this evening, extending
into the early morning hours (Figure 14). In the country a single jetlet
was well established by shortly after sunset and continued at a height of
about 125 to 150 m throughout the night. The maximum wind speed however
occurred in the middle of the night and had started to decrease by the
morning hours. Multiple low level maxima in wind speed occurred in
downtown St. Louis. The main layer of maximum speed was based between 200
and 250 m with considerable variation in height with time. The maximum
speed was observed early in the night rather than in the middle, and was
slightly higher than the maximum value in the country. However, it then
decreased so that by the morning hours the maximum speeds in the country
and city were about the same.
The base of the layer of high winds occurred just above the top of the
inversion during most of the night in the city. However, this was the
case only until shortly after 0200 in the country, at which time the
inversion started to deepen significantly but the height of the main
maximum in wind speed remained fairly constant.
SUMMARY
The material above has been presented to illustrate some of the kinds
of information contained in the data collected with the boundary layer
-38-
-------
JULY 25-26, 1975
MIXING RATIO (g/kg)
I //I/7777
a. BP 1, DOWNTOWN
///I/////I///I/////I
b. BP 2, RURAL TRIAD H
500
400
300
S 200
100 -
2000
V///////'///i////
c. URBAN-RURAL DIFFERENCE, BP 1 - BP 2
2200
0400
0000 0200
TIME, CDT
Figure 13. Time-height distributions of a) mixing ratio in downtown St.
Louis, b) mixing ratio at Triad High School which is located in a rural
setting surrounded by farmland, and c) difference in mixing ratio at the
two stations, on the night of July 25-26, 1975. In a) and b) heavy lines
indicate the tops of moisture inversions.
-39-
-------
O
e
«<
Q
O
co
600
500 -
400 -
300 -
5 200 -
(—t
LU
rc
100 -
0
2000
2200 0000 0200
TIME, CDT
JULY 25-26, 1975
WIND SPEED (mps)
b. BP 2, RURAL (TRIAD H.S.)
0400 2000
2200 0000 0200
TIME, CDT
0400
Figure 14. Time-height distributions of wind speed on the
night of July 25-26, 1975, as measured by boundary layer
profilers a) in downtown St. Louis and b) at Triad High
School located in a rural setting surrrounded by farmland.
The shaded areas indicate regions of maxima and the heavy
lines the peak values in the vertical profiles.
-------
profiler. These examples indicate that a great deal can be learned about
the evolution of the structure in the lower PEL from these data. In the
currently funded studies of the turbulent fluxes the profiler data will be
used in quite a different manner. However it is the intention to seek
funding at a later date to do intensive studies of the evolution of PEL
structure over the inner city and country surfaces.
REFERENCES
1. Ackerman, B. Winds in the Ekman layer over St. Louis. Preprints,
Conf. on Urban Environment and Second Conference on Biometerology,
Philadelphia, Pennsylvania, October 31-November 2, 1972. pp. 22-27.
2. Ackerman, B. METROMEX: Wind Fields Over St. Louis in Undisturbed
Weather. Bull. American Meteorological Society, 55(2):93-94, 1974a.
3. Ackerman, B. Wind Fields Over the St. Louis Metropolitan Area. J. of
Air Pollution Control Assoc., 24(3):232-236, 1974b.
4. Angell, J. K., D. H. Pack, C. R. Dickson, and W. H. Hoecker. Urban
Influence on Nighttime Airflow Estimated from Tetroon Flights. J.
Applied Meteorology, 10(2):194-204, 1971.
5. Angell, J. K., W. H. Hoecker, C. R. Dickson, and D. H. Pack. Urban
Influence on Strong Daytime Flow as Determined from Tetroon Flights.
J. Applied Meteorology, 12(6):924-936, 1973.
6. Blakadar, A. K. Boundary Layer Wind Maxima and Their Significance for
the Growth of Nocturnal Inversions. Bull. American Meteorological
Society, 38(5):283-290. 1957.
7. Bowne, N. E., and J. T. Ball. Observational Comparison of Rural and
Urban Boundary Layer Turbulence. J. Applied Meteorology,
9(6):862-873, 1970.
8. Chandler, T. J. Wind as a Factor of Urban Temperatures, a Survey in
Northeast London. Weather, 15(6):204-213, 1960.
9. Findlay, B. F., and M. S. Hirt. An Urban-Induced Meso-Circulation.
Atmospheric Environment, 3(5):537-542, 1969.
10. Mass, W. A., W. H. Hoecker, D. H. Pack, and J. K. Angell. Analysis of
Low-Level, Constant Volume Balloon (Tetroon) Flights over New York
City. Quarterly J. of Royal Meteorological Society, 93(398):483-493,
1967.
11. Morris, A. L., D. B. Call, and R. B. McBeth. A Small Tethered Balloon
Sounding System. Bull. American Meteorological Society,
56(9):964-969, 1975.
12. Thyer, N. Double Theodolite Pibal Evaluation by Computer. J. Applied
Meteorology, l(l):66-68, 1962.
-41-
-------
APPENDIX A
AVAILABILITY OF DATA:BOUNDARY LAYER PROFILES
The availability of useable profile data collected in the ISWS
Boundary Layer Program during the field efforts in 1975 are shown in the
following three tables.
Tables A-l and A-2 show the times and stations for which wind profiles
obtained using pilot balloons are available. Table A-3 shows the times and
stations for which temperature, humidity and wind profiles obtained with
the boundary layer profiler (tethered balloon) system are available. The
locations of all stations are shown in Figure Al.
The equipment and techniques used in both systems are described in the
main body of this report. All the data are archived on 9-track-1600 BPI
magnetic tapes in IBM unformatted binary code.
-42-
-------
Table Al. Pilot balloon measurements available for
February 1975.
Symbols: 0 = no data, / = data to 200 m of ni,jner, = d.na _,;„. ;....,s >.nan ±<)0 ">.
SITE DATE RELEASE Tim, (local)**
19 Feb. 1220 1240 1300 1320 1400 1420 1U40 1500
33 v'///////
<*<» •///////
71 0 / / / Q / /
75 /O //////
78 / 0 / / 0 0 / o
79 ////////
20 Feb. 1150 1210 1230 1250 1340 1400 1420 1440
33 0 ///////
44 ////////
71 ////O///
75 ////////
79 ////////
21 Feb. 1140 1200 1220 1240 1330 1350 1410 1430
33 ////////
44 ////////
71 ///O////
75 /////// 0
79 ////////
25 Feb. 1320 1340 1400 1420 1440 1500
33 0 0 0 0 / /
44 //////
71 0 / / / / /
75 0 0 / / /
78 //////
79 0 / / / / /
* 26 Feb. 1220 1240 1300 1320 1400 1420 1440 1500 1520
74 /V////*/>'/v/
75 /////////
79 //////*^^^
74
75
79
1230 1250 1310 1330 1410 1430 1450 1510 1530
27 Feb. 1210 1230 1250 1310 1350 1410 1430 1450
33 ///////
1*4 ///////
•jl 00/OQ03
74 //////''
75 0 0 0 0 / J *'
79 Q J •! '•'''
33
78
1240 1300 1320 1340 1400 1420 1440 1500
* = W nin staggered releases at situs S3 and 78, 2 to
-------
Table A2. Pilot balloon measurements available for
July 1975
= n,: data, J = data to 200 m ur hi,jhr>rt - = data for less than 200 m.
.ire
i*U
7?
7«
7 -
Vi
• i'i
1.'
J'l
7 «
7 -
7 ,
74
70
7 •
33
I'-
ll
76
Hit
7 i
17
7R
71
T>
1-
i -
7-i
7 '
7,\
'••'.
7 ,
~,,
~.ii
~~
L-\i;; :J::I;A,;I; Tint;;; /,-;'/•; SITC DATL
' July i. 0 11 ?) ll'*0 12'»'i 12"! 11'iu 13?0 13MO 18 July 11? / /
-j 0 0 0 / / / / 78 ° ^
7 'ulv IV ' iVO 11<"0 11J>" I1'«0 K/'O 1'.20 15UO ii.O'J 1-.20 * ?1 July 1320 ITi-)
/ / / / 0 / / / / 70 / /
/ / / / / 0 / / / / 7'J / /
l/ ^ %/ ' '* ' , , , y i .no 1 V'<)
//»•'// n ////„. < / J
, , , , , , , • 70 t »
. / » / / ')//•' •' ./M ^ /
-n ,'uiv J, i! i.""-" J3lih rn-j i i1.') J'no I'i'.'j JMO !''*'> ?•' ^ /
*'/*/!////// ?? Jujy i:';'') iri" '
»'»//// » 77 / /
l/n • nr'0 i jjo 1310 I'ton jnuo J'jO^ ii)?o 1510 7'i / /
/ • / / r' 0 / / / 71) / /
,/ ,' /////// 7H / /
,-10 July .140 2r,0 222C, 2>0 2320 2340 WOO 0020 ^ ?"-25 July 213^ 21!^
^ '',,,, 1 72 ' //
0 0 y .'//// - / /
/ / ,',//.'/ '| / /
/ °, / ^ /'/'// 7'3 / /
10-11 Julv 2140 2200 2220 224, 2320 2340 2m,o 0020 w ""^ Jul>' 21^ ?1"°
o .' a o o o o ^ v^ ^
' '/ /''//// 7t ^ •'
-','// / / ,' / 7S
12 lulv 1'"') 1400 1420 144,' i:,21' r,4') ll-OO lf;20 20-:7 ..'uly 2140 2200
.' / / / / 0 0 1 44 / /
,,','/.'/// 70 / /
,' / ,' /,''/// 72 / /
,' ,' ,','//.' 74 / /
/,'//,/ 0 71 / /
•|" J'jlv 1'J'l 1 1 iO 13r:0 I'll') !4r.T 1510 1530 1550 1G30 2'j July Ot.OO 01,2-)
///////// 70 / /
v //,'// /c 79 /
V. Julv 1..M 1340 1»00 1«2'.. 1440 1520 154C 160U 1620 ^ 2°JUly 002J °°^
'./'!///'// 7'J / /
//////// / ?'J July 12"° 130°
'i !ulv li!" 1.110 1350 1411 I'lbO 11.10 1S)0 1550 1610 73 0 /
/ '/ y • / , / 30 July OC'OO 0020
' 70 J /
/ / / / / ^ / / / 30 July 0920 0040
;i .' / ,'///// 70 o o
/ ,'///// 79 ,' /
!• .;.!-, i.-,-; .;:-> 12-0 noo 1340 IMOO 1420 1440 1500 70 30 July 12"^ "™
'- *' *^ ' J ' "j j J ~1'- / /
.' / / •)//// / 31 -July 0'J2? 03'»3
/ / -'' / .' / / / 33 TO .IP 2 / r'
. t i' / / / / / / 'J / /
1
1 / /
ii / /
MELLASL TIHCSfr.V'r;
12')0 l?2i) 1210 13.X) 1310
/ / / 0 0
/ / / / /
/ / / / 0
/ / / / /
/ / / 0 0
1100 m?n I'joo irj^o IMO
/ / / / /
////"/
11 |0 Hl.i'i 11', 0 JSno l!i'-0
/ / / / /
/ / / / /
)inn |')>o llif) ]'»?o 3'tlO
/ / / / /
/ / / / /
/,'///
/////
2210 2230 2310 2330 2350
/,'///
/ / / / 0
///'//
2200 2220 2300 2320 ?340
////!-
i i ,' / :'
222" 2240 2320 2340 f'OOO
/ / / / /
0 / •' / /
///.'/
t1 J J J J
/ / / / /
01,1)0 ,700 0740 0800 OS2'.)
/ / / / /
0 0 0 / /
1000 1020 1040 1120 11UO
/ / / / r'
////,'
1320 1340 1400 1440 1500
/ / ,' / /
01>4U 0700 0740 O8'~,0 0820
/ >' / / /
1000 1020 104'.' 1120 1140
00000
/ / / / /
1320 1340 1UOO 1420 14'H)
/ 0 / / r'
/ / / 0 0
10UO I'i20 1045 1100 1120
/ / / ,.' ,,'
,' /
/ / / / /
/ / / / t
/ ,'/,'/
,.,/ n/.'.-o 70 .fll ?.', /:.-.. ,', ew
1400 1420
0 0
/ /
0 0
/ /
0 0
1003 1020
0 /
/ /
11, .10 11.30
/ /
/ /
K'lO 11,20
/ ,'
/ /
/ /
/ /
0010
J
/
0
I/
0000
•'
^
0'J20
,'
»'
/
/
/
0-41! .MOO
l' /
/ /
UOO 1,-JO
/ ,'
1520 1540
/ ,'
lbi.0 0100
<'t >'f
12' "J ]22'J
i /
,' /
1 'i'10
'.'
115-
,''
/
/
,,'
/
• ;: .l.'k ;?'':.
-44-
-------
Table A3. Availability of data from tethered balloon,
boundary layer profilers. Times, sites when
useable data are available are shown by
/ symbol.
STN. DATE SOUNDING TIMES
2 July 1210 1*05
BPI
3 July 1115 1300 1*00 1500 1600
BPI / / /
BP2 / /
5 July 1100 11*0 1220 1300 13*0 1*20
BPI / /
BP2 //////
7 July 1300 1330 1*00 1*30 1500 1530 1600 1630 1700 1730
BPI ////////
BP2 J / //////
8 July 1200 12*0 1320 1*00 l**0 1520 1600 16*0
BPI / /
BP2 //////
9-10 July 2120 2200 22*0 2320 0000 00*0
BPI /////'/
1* July 1300 13*0 1*20 1500 15*0 1620 1700
BP1 / / / / /
BP2 / / /
15 July 1220 1300 13*0 1*20 1500 15*0 1620 1700
BPI / / / / /
BP2 ////////
16 July !2*0 1320 1*00 1**0
BPI / / / /
"BP2 / / / /
18 July 10*0 1120 1200 12*0 1320
BPI / / / / /
*BP2 / / /
21 July 1200 12*0 1320 1*00 l**0 1520 1600 16*0 1720
BPI /////////
BP2 ////////
22 July 1200 12*0 ^320 1*00 1**0 1520 1600 16*0 1720
BPI /////////
2*-25 July 19*0 2020 2100 21*0 2220 2300 23*0 0020 0100
BPI /////////
BP2 /////////
25-26 July 20*0 2120 2200 22*0 2320 0000 00*0 0120 0220 0320 0*20
BP, ///////////
BP2 /////// / /
26-27 July 2020 2100 21*0 2220 2300 23*0 0020
BPt //////
BP2 / / / / /
27 July 1220 1300 13*0 1*20 1500 15*0
BPI / / / /
28 July 1700 17*0 1820 1900 19*0 2020 2100 21*0
BPI / / / >' •' >' *' '
29 July 0020 0100 01*0 0220 0300 03*0 0*20 0500 05*0 0620 0700
BPI ////// / / / .'
29 July 07*0 0820 0900 09*0 1020 1100 11*0 1220 1300 1*00 1500
BPI ////////
30 ju|y 0820 08*0 0900 0920 1000 MOO 1200 1300 1*00 1500
BPI / / /////«
<>; tlh-rm.wicl-cr trulfwu-li
-------
Figure A-l. Locations of the double-theodolite pilot-balloon
observing sites (numbered) and the two boundary-layer profiler
stations, BP1 and BP2.
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APPENDIX B
AN INVESTIGATION OF THE ERRORS IN ESTIMATING WIND VELOCITY
BY DOUBLE-THEODOLITE PILOT-BALLOON OBSERVATIONS
INTRODUCTION
In studying the planetary boundary layer (PEL) wind field over a small
meso-scale region such as the METROMEX area (4000 or 5000 km ) it is
important to establish that the observed variations are larger than the
"noise" arising from errors in the basic measurements. Thus an
investigation of the probable error in the estimates of wind velocity
obtained in the ISWS boundary layer program has been an integral part of
the overall effort.
Measurement of wind in the PBL over the complex meso-region around St.
Louis has been by visual tracking of pilot balloons in the ISWS field
programs. Field efforts designed to provide detailed study of the velocity
structure has utilized two theodolites, spaced a few hundred meters apart,
to track the balloons (double theodolite system). The double theodolite-
system is an improvement over single theodolite tracking since it does not
require the assumption of a constant rate of balloon ascent, an assumptict,
which is poorly justified for the PBL, particularly during summer days.
Nevertheless, there are still several potential sources of error in the
wind estimate, arising from both human and equipment factors.
Three potential sources of error were recognized before the field
efforts began in 1971 and procedures were incorporated to minimize their
effects on the measurements. These expected sources of uncertainty were
(1) observer stress and fatigue, (2) faulty equipment, and (3) faulty
orientation of the theodolite in the horizontal plane (level) and/or in the
horizontal coordinate system (azimuthal orientation).
Human stress and mental and physical fatigue are factors in any type
of prolonged use of a precision instrument. Bellucci (1960) has discussed
the importance of experience when accurate measurements for frequently
launched balloons are needed. High observational frequency (frequent dial
readings) is needed for good vertical resolution in the profiles but
increases fatigue and decreases reading accuracy. Barnett and Clarkson
(1955) have reported that measurement error decreased rapidly with
The analysis of the test data was carried out by W. J. Mansell.
This analysis was supported by funds from the National Science Foundation
under grant number DES 74-13931.
-47-
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decreasing observing frequency, reaching an acceptable level at 20-sec
observation interval with no significant improvement for longer intervals.
Rachele and Duncan (1967) also report that a better estimate of the average
wind in a layer is obtained by several readings within a layer but
concluded that for a layer depth comparable to 20-sec reading interval
single readings at this rate does just as well as more frequent readings.
In order to minimize the human stress and fatigue while maximizing the
vertical and temporal resolution of the wind profiles the following
procedures were followed: (1) special additional training and practice
were given to already experienced observers; (2) a 20-sec measurement
interval was used; (3) the balloon was tracked for only 13 minutes out of
each 20-min; and (4) a 30-min break was provided midway during the 3-hr
experimental period.
i
Theodolites are precision mechanical instruments and, although hardy,
are not immune to problems. The theodolites were thoroughly checked and
adjusted by skilled technicians prior to the field programs. In addition
the observers checked their equipment daily and any problems detected were
rectified before the next operation. However transport in military trucks
is hard on precision equipment and it was not uncommon for misalignment
between short- and long-range optics or loosening of the gears to occur.
The observers recorded when they shifted from short to long scope and if
there was misalignment (evident as a single spike in the processed data)
the resultant error w^,~. corrected. Errors resulting from slippage of the
gear train are frequently detectable and correctable using the Thyer
computational method.
A theodolite can lose orientation in the horizontal plane (level) in
several ways. For instance, the observer may accidentally jar the tripod
or the tripod may settle unevenly, particularly in soft soil. The
observers carefully leveled the theodolite at the beginning of the
experiment and checked the level periodically during the observational
period. Azimuthal orientation in the fixed cartesian coordinate system was
accomplished by lining up on the marker at the opposite end of the baseline
and on two other marked landmarks off the baseline which had been
established when the site was surveyed. The theodolite was
azinuthally-oriented at the beginning of the period and checked for azimuth
to at least one of the markers once or twice during the experiment.
Although it is believed that the procedures described above helped to
reduce errors in the measurements, it is unlikely that they erased them.
Consequently special field tests were conducted in the summers of 1972 and
1975 in order to establish the probable errors in the measurements of wind
speed, wind direction, height of the balloon, and balloon ascent rate
obtained with the double theodolite systems used in the boundary layer pro-
gram. These tests were made during the forenoon of August 1, 1972 (Test
I), late afternoon of August 9, 1972 (Test II) and forenoon of July 31,
1975 (Test III) using the same observers and equipment as were used during
the field experiments of those years. The tests were all carried out at
Scott Air Force Base, Illinois, about 30 km southeast of St. Louis,
Missouri. The local terrain is mostly level farmland with sparse
population. The upwind fetch for the test days was fairly flat with some
slight roll.
-48-
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TEST PROCEDURES
The design of the test was very simple. Several teams set up along
parallel baselines tracked a common balloon, making synchronized readings
to the balloon at 20-sec intervals. In the 1972 tests the mini-network
consisted of 8 observers utilized as 4 double theodolite teams (Figure
B-la). All baselines were the same length (about 610 m) and were separated
from their nearest neighbors by 7.6 m. The mini-network used during the
1975 _ test was similar (Figure B-lb). Ten observers were involved,
providing 5 double theodolite teams. Baseline separations were 3.1 m and
baseline lengths were 656.8 m. In all tests the balloons were released
from the center of the perpendicular to the baselines at the downwind end
of network. The baselines were aligned approximately NW-SE.
On each test day, 30-gm balloons were released every 20-min during the
testing period. On Tests I and II (August 1 and August 9, 1972), 6
releases were made during the testing period, while on Test III (July 31,
1975), 8 releases were made. All teams tracked each balloon. Angular
measurements to the balloon were made by each team every 20 seconds using
synchronized timers. Angles were read from the theodolite dials to the
nearest tenth of a degree with an estimate of the nearest hundreth of a
degree and were orally recorded on cassette tape recorders. The timer and
recorder systems, the measurement interval and the angular resolutions were
all identical with procedures used during the field experiments.
In order to determine the magnitudes of errors introduced when
theodolites were improperly leveled or azimuthally-oriented, one theodolite
was purposely misoriented by 1° or tilted by 1 bubble during a couple of
test runs on each test day. Azimuth orientation errors of one degree are
small and may easily occur due to slackness in the theodolite gears. Error
in vertical orientation (level) of this magnitude is extreme and is
unlikely to occur except in cases of settling on very soft ground or
accidental jostling of the tripod.
A total of 88 independent double-theodolite estimates of mean wind
profiles were collected, 24 on each of the two test days in 1972, and 40 on
the test day in 1975. The basic data were computer processed using the
Thyer (1962) technique and carefully edited for errors due to obviously
misread angles.
ERROR ANALYSIS
Since there are no standards available against which to check the
observations, the "true" wind was assumed to be the average of the
independent estimates made by the double theodolite teams. In carrying out
the analysis, the square root of the pooled variance taken over all teams
and all balloon releases during a given test period was considered the best
estimate of the probable error in the estimate of the parameter of
interest. Only measurements taken by teams with properly oriented
theodolites were used in the calculation of these estimates, i.e.,
measurements IHvolving~~deTIberaTely misoriented or tilted theodolites as
mentioned in the preceding section were excluded from the analysis.
-49-
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BALLOON RELEASE
TEST I
BALLOON RELEASE.
TEST II
-609.6 m-
(a)
TEAM
BALLOON RELEASE
TEST III
Figure B-l. The "mini-networks" used in tests of the accuracy
of the double-theodolite pilot-balloon wind-measuring system
in (a) 1972 and (b) 1975. The two men on each team were placed
at opposite ends of. a baseline as indicated by the heavy dots
and matched team numbers.
-50-
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All three tests were carried out on days of undisturbed weather. The
profiles of mean wind direction (relative to baseline coordinates, with 0°
looking along baseline from the release end) during the test periods are
shown in Figure B-2 for all three tests. Also shown are bars of + one
standard deviation (la) calculated from the averages of the several
estimates on each run to indicate the temporal variability.
The profiles of the mean wind speed for the test periods and the
la values of temporal variability are shown in Figures B-3. The winds dur-
ing test period I were southerly 4 to 4.5 mps and fairly constant with
height. During the third test, the winds were southeasterly or ESE
throughout the lower 1.5 km, but the wind speeds, which were 5 to 6 mps
below 500 m, gradually increased with height to about 12 mps at 1.5 km.
The winds were lightest during Test II, ranging from 3 to 4 mps in the
lowest kilometer. There was a zone of rapidly shifting winds during Test
II, with backing from a northeasterly direction below 500 m to NNW at about
1.2 kilometers.
In order to establish estimates of probable errors in wind speed,
direction, rise rate and balloon height, the pooled variances (over all
releases) for each of these parameters were calculated for every 20-sec
layer on each of the three test periods. The square root of the pooled
variance for any one variable is taken as the best estimate of the probable
error in that variable, and is the quantity discussed below. The
discussion is confined to the layer below the level where, due to missing
data, less than 50% of the maximum number of available degrees of freedom
were used in calculating the statistic.
Error in Wind Direction
The estimated error in wind direction was only 1 or 2 degrees for
Tests I and II and 2 or 3 degrees for Test III (Fig. B-4). The error in
wind direction tends to be largest in the first 100 m because the short
range to the balloon and its rapidly changing position as it responds to
the unsteady low level winds make it extremely difficult to keep the
balloon on the cross-hairs of the theodolite. The error tends to become
larger again above a kilometer or so, a consequence of the fact that
position errors for small angular errors are amplified as the range to the
balloon increases. Comparison of the error to the temporal variability in
the mean wind direction (Fig. B-2) clearly shows that the error is
considerably less than the temporal variability, particularly below 1 km.
Error in Wind Speed
The estimated error in the wind speed is shown as a function of height
for all three tests in Fig. B-5a. It was smallest during Test II on August
9, 1972, ranging from 0.2 to 0.3 mps in the first 1200 m, increasing with
height to 0.8 mps at 1600 m. The average wind speed for this test
increased from 3 mps at the surface to about 7.5 mps at 1600 m (Fig. B-3b).
Thus the percentage error increased from 3% at 200 m, to 5% at 1 km to 10%
at 1600 m.
-51-
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AVERAGE WIND DIRECTION, BASELINE COORDINATES (degrees)
Figure B-2. Mean profiles of wind direction, in baseline
coordinates, taken over the test duration for the three tests
of the accuracy of the double-theodolite pibal wind-measuring
system. The horizontal bars are a measure of the temporal
variability (± 1 root-mean square deviation calculated from
the average for each balloon launch).
-52-
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8 0
2 4 6 8 10 0 2
MEAN WIND SPEED (mps)
10 12 14 16
Figure B-3. Mean profiles of wind speed (solid line) for the
duration of each of the three double-theodolite accuracy tests.
The small +'s give a measure of the temporal variability as
indicated by ± 1 RMS deviation calculated from the average
profiles for each balloon launch.
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246
RMS ERROR,
WIND DIRECTION (deg)
Figure B-4. Profiles of the estimated error in wind direction,
for three tests of the accuracy of the double-theodolite wind
measurement.
-54-
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RMS VECTOR ERROR (mps}
Figure B-5. Profiles of the estimated error in wind speed and
of the estimated vector error for three tests of the accuracy
of the double-theodolite wind measurement.
-55-
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During Test I, the estimated error below 1 km was between 0.4 and 0.6
raps, roughly 10% of the average speed during the test. (The spike at 200 m
was due to the switch from short to long scope by one team. As mentioned
above this is a correctable error but has been left in in this instance to
demonstrate the magnitude of the error when the two scopes are badly out of
alignment.) The estimated error from Test III is quite a bit larger than
that for either of the other two tests ranging from 0.6 mps (12% of the
mean wind) at 200 m to 2 mps (20% of the average wind) at 1 km.
It can be seen from Fig. B-3 that the estimated error was much smaller
than the temporal variability in the mean wind speed during Test II and was
less than half the temporal variability of the mean wind during Test I.
During Test III, the estimated error was roughly half the temporal
variability below 600 or 700 m but above that,level approached the temporal
variability.
Vector Error
The root-mean-square vector error is shown in Fig. B-5. Considering
the small error indicated for the wind direction, it is not surprising that
the profile for the RMS vector error is similar to the error profile for
the wind speed. The conclusions to be drawn are the same as that drawn for
wind speed, i.e., significantly smaller values for the first two tests than
for the third, and increasing vector error above a kilometer, particularly
during the third test period.
Error in Calculated Balloon Ascent Rate
The double theodolite computations yield the values of the three
components of the balloon velocity, so that no assumptions are made as to
constancy of balloon ascent rate,. Nevertheless during the field
experiments the amount of helium used to inflate the balloon was kept
constant, to within the accuracy of the meters used to measure the gas
flow. Thus in still air the ascent of the balloon would have always been
the same, and errors could have been determined from the difference between
calculated and design ascent rates. However, the atmosphere is seldom
still and the rate at which the balloon rises is strongly affected by the
vertical motions of the air. In Figure B-6 a to c are shown the profiles
of computed ascent rate and the temporal variability, as indicated by the
RMS deviations of the average profiles for each release. The ascent rate
tends to "settle down" at about 800 m (in the mean) to about 2.1 or 2.2
mps, which was the design value, but varied considerably from this in the
lower levels.
The profiles of estimated error in the balloon ascent rate is shown in
Fig. B-6d. Again the error was smallest for Test II, nearly uniform at 0.1
to 0.2 mps up to 1200 m (representing 5 to 10% of the average rate of
rise), and then increasing slightly about 1200 m. The estimated error in
the first test period was about twice that of the second, at least up to
the 1 km level. The profile of estimated error for ascent rate during Test
III exhibited characteristics similar to that for the wind speed. The
errors on Test III were comparable to those on the other two tests in the
-56-
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lower layers, but increased with height so that by a kilometer they were
larger by a factor of three.
Error in Balloon Height
The profiles of the estimated error in the height of the balloon at
each 20-second reading are shown in Fig. B-7. It should be pointed out
that each height estimate is independent since the calculation uses
independent angular measurements and time. The height error increases with
height, partly a consequence of increasing position error for a given
angular error as the range to the balloon increases.
By and large the errors in height are not significant below 500 m
(less than 20 m), only a few per cent of the height. In fact the errors
remain insignificant for the first two tests to at least a kilometer.
Although the height error estimated on Test HI was nearly the same as the
estimates on the other days up to 600 m, it increased rapidly above that,
reaching 10% of the height at 1200 m.
DISCUSSION
Field tests of the double theodolite systems used in the ISWS boundary
layer program have provided estimates of errors that must be taken into
account in interpreting the results of the field experiments. These tests
indicate that for the lowest 500 or 600 m the probable errors are not
excessive and, at least for wind direction, are not significant. Moreover
it has been shown that up to 500 or 600 m the error is considerably less
than the temporal (non-systematic) variability expected over two or three
hours. Although the errors may remain small to a kilometer or more under
certain wind conditions, the non-uniformity of the results from the three
tests indicate that they can become significant under other conditions.
The differences in the results for the three test periods point up a
niaiber of factors that need to be considered in estimating possible error
in wind measurements by the double theodolite tracking of balloons.
AJ-\iough the basic systems were the same on the three tests, the components
ivere not identical, i.e., both men and equipment were different on the
three days. During Test I there were more than the usual number of
problems with one of the theodolites, which, despite realignment at the
beginning of each run, would not maintain orientation through the 10 or 12
minute tracking period. This may help to explain why the error was larger
on this test than on Test II. However, no unusually-faulty equipment was
noted for Test III, which provided larger estimates of error than the other
two tests.
A more reasonable explanation of the differences of the results of the
three tests appear to lie in the differences in wind speed and in the
crossing angle between the balloon track and the baseline. In
computational techniques which use only three of the four angles available,
the advantage of the double theodolite tracking over single theodolite
sighting decreases as the wind direction (and therefore the balloon track
angle) approaches the angle of the baseline, and in fact the computations
fail when they are parallel.
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40
80 120 160 200
RMS ERROR, HEIGHT (m)
240
Figure B-7. Profile of the estimated error in the
height of the measurement for the three tests of
the accuracy of the double-theodolite wind
measurement.
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Although the computation using Thyer's technique does not fail when
the crossing angle of the balloon path and the baseline is zero, it appears
that errors tend to be amplified when this angle is small. It can be seen
from Fig. B-2 that during Test III when the errors were largest, the wind
was almost parallel to the baseline and therefore the balloon track was
almost along the baseline. Thus the triangle to be solved was very
oblique. On the other hand, during Test II when the errors were smallest,
the wind in the lowest 500 m was about 90° to the baseline, and although it
backed to a 20° relative angle at 1200 m, by that time the balloon had been
carried out about 2 km perpendicular to the baseline so that the triangle
to be solved was still very acute. The winds during Test I were about 45°
to the baselines, and the indicated error remained fairly small.
i
Wind speed can affect accuracy in two ways. The stronger the wind,
the more difficult it becomes to keep the balloon on the theodolite
cross-hairs, both because of its more rapid movement and because in the
PBL, strong winds are frequently more turbulent, causing the balloon to
bounce around. In addition strong winds cause the range to the balloon to
increase rapidly and although it is usually easier to track balloons when
they are far away, small errors in angle readings result in large position
errors.
In this set of tests, the "crossing" angle and wind speed are coupled
in such a way that it is not possible to separate the effects of the
factors discussed above, i.e., the lowest wind speed occurred on the day
when the crossing angle was largest and strongest wind on the day the
crossing angle was smallest. However, a close examination of the data
indicates that the error in measurements of wind speed is probably more a
function of the low-level wind direction (relative to the baseline) than
the wind speed. This may be true , also for the error in wind direction,
although the increase in the error with height above a kilometer suggests
that the range to the balloon may be a factor of some importance here.
REFERENCES
1. Barnett, K. M., and 0. Clarkson, Jr. Relation of Time Interval to the
Accuracy of Double Theodolite Observations. Monthly Weather Review.
93(6):377-379.
2. Bellucci, R. L. Preliminary Estimates of Variability of Winds in the
Lowest 500 Feet. U. S. Army, USAARDL Technical Report 2122, U. S.
Army Signal Research and Development Laboratory. 15 June 1960. 16
pp.
3. Rachele, H., and L. D. Duncan. Desirability of Using a Fast Sampling
Rate for Computing Wind Velocity from Pilot Balloon Data. Monthly
Weather Review. 95(4):198-202. 1967.
4. Thyer, N. Double Theodolite Pibal Evaluation by Computer. J. Applied
Meteorology. l(l):66-68. 1962.
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APPENDIX C
SURVEY POLICY REGARDING
FURNISHING DATA TO OUTSIDE AGENCIES
In the course of conducting research or investigations the Survey may
accumulate valuable, even unique, collections of data. These data may have
been collected and processed into useful form either at State expense or in
connection with grants or contracts.
It is expected that such data will be used initially and primarily for
interpretive studies and publications by the Survey. However, the data
may have values for studies of a related or quite unrelated nature by other
organizations. Such outside use may produce further understanding of
Illinois resources, represent valuable contributions to science, and
enhance the scientific reputation of the Survey, However, reasonable care
must be exercised that responsible organizations or individuals propose to
make proper use of the data. It is also recognized that substantial
personnel and machine time may be involved in responding to a data request.
This statement sets forth a policy under which such data may be
furnished to other agencies.
1. Decisions regarding furnishing data to outside individuals or
agencies shall be made by the Chief of the respective Survey.
2. Data are to be furnished only to responsible scientists and
research or user agencies which establish a legitimate need for
such data.
3. The requesting agency shall furnish a written description of the
desired data and its proposed use.
4. Copies of published or unpublished reports containing results
derived from the outside analyses are to be supplied to the
Survey without charge.
5. Such requests from agencies of Illinois or agencies who
participated in the funding of the data acquisition will be
without charge. Requests from other individuals or agencies
will be assessed a reasonable charge to cover the cost of making
the data available. Such payment is to be deposited with the
State of Illinois or with the Survey's Indirect Cost Account as
the Chief considers appropriate.
December 8, 1970
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO 2.
EPA.-60Q/4 - 77-045
4. TITLE A\D SUBTITLE
VERTICAL FLUXES AND EXCHANGE COEFFICIENTS IN THE
AIR OVER ST. LOUIS
Field Program 1975
3. RECIPIENT'S ACCESSION-NO.
5, REPORT DATE
November 1977
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
Bernice Ackerman
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Illinois State Water Survey
Urbana, Illinois 61801
10. PROGRAM ELEMENT NO.
1AA603
11. CONTRACT/GRANT NO.
R803682
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTF, N.C.
Office of Research and Development
Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
IS. ABSTRACT
A field program'was carried out in the greater metropolitan area of St. Lous, MO
during February and July of 1975 as part of the Regional Air Pollution Study (RAPS).
Die purpose of the program was to collect atmospheric measurements needed for future
studies of the planetary boundary layer (PEL) over urban and industrial areas and sur-
rounding rural areas. The overall goals of the PEL study are to (1) describe the ther-
nodynamic, wind and turbulence fields over the region; (.2) determine the magnitude and
vertical variation of the vertical fluxes of heat, moisture and momentum as a function
of land use; (3) obtain estimates of the exchange coefficients of these variables; and
(4) determine the dependence of turbulence intensity on land use. Pilot-balloon station;
provided simultaneous measurements of the wind profile with vertical resolution. Teth-
ered-balloon sounding systems yielded thermodynamic and wind profiles. An airplane
equipped with meteorological instruments provided measurements of the three components
of wind velocity and -of high frequency fluctuations in velocity, temperature and
humidity.
Observational periods, or missions, were scheduled for 3-or 4-hour durations
during field experiments. The objectives included (a) mapping missions to delineate
the thermodynamic, wind and turbulent fields over the region, (b) flux missions to
provide estimates of the true vertical fluxes of momentum, heat and moisture simulta-
neously with vertical profiles of these variables,and (c) nocturnal missions to
fide infer
;th of th
:turanl heat island circulationi
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Air pollution
*Meteorological Data
Measurement
Boundary Layer
St. Louis, MO
13B
04B
20D
. ^l?T^ISUTION STATEMENT
RELEASE TO PUBLIC
19. SECU
21. NO. OF PAGES
72
20. SECURITY CLASS (This page I
UNCLASSIFIED
22. PRICE
E°A form 2220-1 (9-73)
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