EPA-650/4-74-007
April 1974
Environmental Monitoring Series
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EPA-650/4-74-007
DETERMINATION
OF ENERGETIC CHARACTERISTICS
OF URBAN-RURAL SURFACES
IN THE GREATER ST. LOUIS AREA
by
W. F. Dabberdt and P. A. Davis
Stanford Research Institute
Menlo Park, California 94025
Contract No. 68-02-1015
Project No. 26AAI/J6
Program Element No. 1AA003
EPA Project Officer: James L. McElroy
Meteorology Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
April 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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ABSTRACT
The role of surface geophysical characteristics (e.g., albedo,
thermal admittance, Bowen ratio, emissivity) in the partitioning of
energy at the complex and heterogeneous metropolitan earth-air interface
has been evaluated through a unique application of Lettau's climatonomy
theory. In contrast to the conventional approach that first specifies
an inventory of "appropriate" surface descriptors and then attempts to
evaluate or interpret observed climatic features, the climatonomical
methodology permits the determination of the surface descriptors on the
basis of the observed diurnal response of the surface to the observed
forcing function of available solar energy. Features of various land-
use types (e.g., farmland, suburban residential, commercial) can then be
evaluated in the context of the surface energy budget. For example, if
the subsurface heat flux is treated by assuming the medium is a homogeneous
conductor, then an effective thermal admittance is derived that satisfies
the assumption and the observed diurnal response of surface temperature.
During three designated experimental periods, totalling some 50
hours, that began with clear skies and reasonably steady meteorological
conditions, aircraft data-collection missions were flown repetitively at
*
2-3 hour intervals from altitudes of 460 m and 1220 m mgl along a selected
flight track across the St. Louis area. Aircraft data included temporal
and spatial measurements of downwelling and upwelling solar radiation,
the effective surface radiative temperature, and the air temperature.
Continuous records of downwelling solar and atmospheric irradiances were
obtained at a single surface station located adjacent to the flight track.
*
Above mean ground level.
iii
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The feasibility of implementing the climatonomical approach was
evaluated on the basis of experimental data obtained on 9 August 1972;
abrupt weather changes occurred during the other two periods and limited
their suitability for extensive analysis. Albedos over the various land-
use types showed a maximum near 16 percent over the rural sites comprising
farms, fields, and woods with a minimum near 13 percent over the older
urban residential and commercial/industrial sites. Urban surface
temperatures were higher than the rural surface temperatures with the
maximum difference (10-15 degrees C) occurring in the early afternoon.
Aircraft albedo and surface temperature measurements, the surface
irradiance measurements, and two balloon soundings of the lower atmosphere
were used in the climatonomical analysis to determine both thermal
addmittance and the inverse Bowen ratio for each of nine land-use sites.
1/2 1
The thermal admittance ranged, from a minimum near 20 mly sec °C
for urban and suburban sites to about 85 for the wooded sections. The
inverse Bowen ratio ranged from 0.22 in the urban area to 2.9 for farmland.
On the basis of the results, the method is judged feasible and
attractive for exploring additional factors, such as the effect of natural
surface alterations (e.g., wetness and ground cover) on the surface
energy budget. The method has significant potential as a tool for applied
studies of climatic effects and modifications relating to land-use planning,
iv
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CONTENTS
ABSTRACT
LIST OF ILLUSTRATIONS vii
LIST OF TABLES xi
FOREWORD xiii
I INTRODUCTION 1
A. Objectives 1
B. Scope 3
II EXPERIMENTAL PROCEDURES 5
A. Surface Observations 5
B. Aircraft Observations 6
C. Data Processing 13
1. Solar radiation 13
2. Surface temperature I 15
III METEOROLOGICAL CONDITIONS 19
A. 9 August 1972 19
B. 11 August 1972 21
C. 23 April 1973 22
IV AIRCRAFT OBSERVATIONS 25
A. Solar Data 25
B. Surface Temperatures 32
C. Air Temperatures 37
V CLIMATONOMICAL ANALYSIS 41
A. Climatonomy Theory 41
B. Method of Approach 47
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V CLIMATONOMICAL ANALYSIS (continued)
C. Application and Results 61
VI CONCLUSIONS AND RECOMMENDATIONS 75
APPENDIX
A AIRCRAFT DATA SUMMARY A-l
REFERENCES R-l
VI
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ILLUSTRATIONS
11 Aero Commander Aircraft of Colorado State University
a) Aero Commander 500 B (left) alongside a Cessna
182 Skylane (right)
b) Interior View of Equipment Rack in Aero Commander .... 8
2 Flight Tracks, Check Points, and Locations Selected
for Harmonic Analysis of Data 10
3 Variations in Response between Wide-Angle and Narrow-
Angle Solarimeter Measurements of Surface Reflectance
and between 4-Degree and 20-Degree Radiometric Measure-
ments of Surface Temperature 14
4 Total Solar and Atmospheric Radiation Incident on
Horizontal Surface, Granite City, Illinois,
9 August, 1972 20
5 Total Solar and Atmospheric Radiation Incident on
Horizontal Surface, Granite City, Illinois,
11 August, 1972 23
6 Aircraft Solar Measurements, 1400 CDT Flight,
9 August, 1972 26
7 Height Variations of Measured Incident Solar Radiation,
11 August 1972 29
8 Normalized Aircraft Solar Measurements, 1700 CST Flight,
23 April 1973 31
9 Aircraft Radiometric Surface Temperature Measurements,
1400 CDT Flight, 9 August 1972 33
10 Normalized Aircraft Radiometric Surface Temperature
Measurements, 1700 CST Flight, 23 April 1973 34
11 Urban and Rural Surface Temperature Variations with Time
(a) 9 August 1972
(b) 23 April 1973 36
vii
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ILLUSTRATIONS (Continued)
12 Aircraft Air Temperature Measurements, 1400 CDT Flight,
9 August 1972 38
13 Site R-l 50
14 Site R-2 50
15 Site R-3 50
16 Site R-4 50
17 Site R-5 51
18 Site R-6 51
19 Site R-7 51
20 Site R-8 51
21 Site R-9 52
22 Near-Surface Meteorological Stations Operated by Illinois
State Water Survey, August 1972 57
23 Comparison of Two-Harmonic Temperature Wave at Station 022
and Two-Harmonic Regression Analysis for Site R-l Using
Data Points 60
24 Effective Surface Radiative Temperature from Two Aircraft
Altitudes at Nine Sites on 9 August 1972 62
25 Diurnal Variation of Derived Departures (from daily average)
of Atmospheric, Latent, and Subsurface Heat Flux Densities
for Three Land-Use Types: Farmland, Commercial/Industrial,
and Suburban Residential 74
viii
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ILLUSTRATIONS (Concluded)
A-l Aircraft Solar Measurements, 0930 CDT Flight,
9 August 1972 A-6
A-2 Aircraft Solar Measurements, 1145 CDT Flight,
9 August 1972 A-7
A-3 Aircraft Solar Measurements, 1400 CDT Flight,
9 August 1972 A-8
A-4 Aircraft Solar Measurements, 1630 CDT Flight,
9 August 1972 A-9
A-5 Aircraft Solar Measurements, 1915 CDT Flight,
9 August 1972 A-10
A-6 Aircraft Solar Measurements, 0900 CDT Flight,
11 August 1972 A-ll
A-7 Aircraft Solar Measurements, 1130 CDT Flight,
11 August 1972 A-12
A-8 Aircraft Solar Measurements, 1400 CDT Flight,
11 August 1972 A-13
A-9 Aircraft Solar Measurements, 1630 CDT Flight,
11 August 1972 A-14
A-10 Aircraft Radiometric Surface Temperature Measurements,
9 August 1972 A-15
A-ll Aircraft Air Temperature Measurements, 9 August 1972 A-17
A-12 Aircraft Radiometric Surface Temperature Measurements,
11 August 1972 A-19
A-13 Aircraft Air Temperature Measurements, 11 August 1972 .... A-21
A-14 Aircraft Radiometric Surface Temperature Measurements,
23 April 1973 A-23
ix
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TABLES
1 Chronological Summary of Aircraft Operations in
St. Louis 11
2 Description of Surface Areas Selected for Analysis 53
3 Results of Harmonic Analysis of 9 August 1972 Surface
Observations of Downwelling Short- and Long-Wave
Radiation at Granite City, Illinois 54
4 Comparison of the 24-Point Harmonic and 8-Point Regression
Analyses of the Near-Surface Ambient Temperature on 9 August
1972 in the Greater St. Louis Area 58
5 Albedo Values for the Nine Surface Areas as Measured on
9 August 1972 from the Two Aircraft Altitudes 66
6 Climatonomic Parameters for 9 August 1972, in the Greater
St. Louis Area 67
7 Derived Amplitude Terms for Atmospheric Sensible, Latent,
and Subsurface Heat Flux Densities 73
xi
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FOREWORD
A large number of people contributed a variety of skills and
services to this program: Contract Manager for the study was Dr. James
L. McElroy, Meteorology Laboratory, National Environmental Research
Center, EPA, Research Triangle Park, N.C.; Ms. Patricia Buder, Research
Meteorologist, and Mr. Hisao Shigeishi, Mathematician, SRI, contributed
significantly in the analysis and processing of the data; Dr. Edward
Uthe, Atmospheric Physicist, SRI, provided the surface radiation data
during August 1972; Dr. William Marlatt, Mr. Don Hill, and Mr. Duane
Adams, Colorado State University, provided the aircraft and instrumen-
tation services under subcontract to SRI; Mr. Stan Changnon, Illinois
State Water Survey, provided near-surface temperature records for
August 1972; the National Weather Service, Lambert Field, St. Louis,
provided forecast information and EMSU soundings; and Dr. Clifford
Murino, Vice President for Research, St. Louis University, kindly assisted
by providing facilities at the University for maintaining and operating
the surface radiation station during April 1973, in cooperation with
Professor Donald E. Martin, Director of Meteorology, and Mr. Louis J.
Hull, both of St. Louis University.
xiii
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I INTRODUCTION
A. Objectives
It is well recognized that the complex air-earth interface plays
an important role in the behavior of the atmospheric planetary boundary
layer and in the differences in the structure of the rural and urban
surface energy budgets. Understanding these differences (and the sub-
sequent partitioning of the net radiation) is further complicated by the
local heterogeneity of individual surface types (i.e., land-use patterns)
and the attendant difficulties in parameterization of the interface
energy fluxes. Conventional approaches toward solution of the problem
implicitly consider the local areas to be homogeneous on the broader
scale, and then proceed to first specify the appropriate surface
geophysical descriptors (e.g., albedo, thermal admittance, roughness) and
subsequently compute the energy fluxes. One of the major difficulties
in this approach is the a priori specification of surface descriptors.
To overcome this obstacle, we have developed and tested a method
whereby these descriptors are determined through an examination of
variations of the surface energy budget as a function of land use, and
the subsequent analysis of these variations in terms of the associated
differences in the geophysical features of the surface. Included among
the surface characteristics are radiative (albedo, emissivity), thermal
(heat capacity, conductivity), and structural (aerodynamic roughness,
height-area-orientation) properties. Radiative and thermal characteristics
are affected by surface wetness, but the importance of evapotranspiration
makes it necessary to add surface "type" as a characteristic, particularly
to distinguish such features as cropland, meadows, parks, and the like.
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To be useful in modeling, the influence of the surface characteristics
on the surface energy budget must be identified, even before associated
feedback reactions with the boundary layer can be considered fully.
The basic objective of this study was the examination of the
variations of the surface energy budget throughout the greater St. Louis
metropolitan area (ranging from rural farmlands to suburbia to the
urban core) so as to evaluate these variations in terms of associated
differences in the thermal, radiative and aerodynamic geophysical features
of the surface. Toward this end, we have drawn heavily from the
climatonomy theory of H. and K. Lettau*1 (1971). In climatonomy, temporal
climatic variations are described analytically as unique response functions
to a prescribed forcing function. More specifically, climatonomy may be
summarized as the quantitative determination of mean values and temporal-
spatial variations of: (1) temperature, the primary response function,
and (2) energy fluxes, the secondary responses (e.g., atmospheric and
subsurface sensible heat exchange, net effective infrared emissions,
evaporation) at a planetary surface in response to the solar forcing
function (i.e., available incident solar radiation).
A major purpose of this study was to examine the feasibility of
obtaining representative empirical data on the spatial and diurnal
variations in the effective geophysical surface characteristics of selected
heterogeneous areas with different surface types. Variations in the
diurnal response of surface temperature are reflected in the secondary
responses and depict the influence of the surface on the establishment of
rural-urban differences in the surface energy budget. This information
should provide a more meaningful classification of distinct surface types
in terms of climatic responses to incident radiation.
*
References are listed at the end of this report.
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B. Scope
The experimental program focused on the acquistion of data on the
spatial and temporal (i.e., diurnal) distribution of surface temperature,
and solar and terrestrial radiation for a variety of surface types. The
data may be conveniently categorized according to source:
Frequent aircraft observations
Continuous surface observations
Supplemental, conventional observations.
The aircraft observations consisted of flights at two-to-three hourly
intervals over a 90-km path centered over the St. Louis urban core; to
obtain as much independent data as possible, the initial and return legs
of each flight were made at different altitudes. The primary aircraft
data included both upwelling and downwelling solar irradiance and effective
surface radiative temperature. Supplemental aircraft observations included
surface photography and ambient temperature. Representative measurements
of the albedo (based on upwelling irradiance measurements) and surface
temperature (based on upwelling radiance measurements) are difficult to
acquire except from a moving platform aloft. In fact, over a very non-
homogeneous surface the only effective means of observing surface temper-
ature is by radiometric techniques applied in a nearly transparent
spectral region. At this stage of investigation no emphasis was given
to a study of direct influences of the atmospheric boundary layer itself
on the radiative processes. Instead, site representative measurements
of total downwelling irradiance were made at one surface so as to
incorporate directly any atmospheric influence. The other principle data
requirement is the boundary layer wind profile; this was available twice-
daily from the nearby Environmental Meteorological Support Unit (EMSU)
station operated by the National Weather Service (NWS) .
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Surface geophysical features derived through the analysis of the
surface response to the radiative forcing function were limited to two
parameters: thermal admittance and inverse Bowen ratio. This limitation
is a result of the number and type of measured values; to derive additional
geophysical features would require additional measurements, such as the
latent or sensible heat fluxes. Even so, certain simplifying assumptions
had to be made: photosynthetic and anthropogenic fluxes of heat were not
treated explicitly in the theory; however, their actual impacts on the
observations are implicit in the data and thus are reflected in the
derived values. On the other hand, the August data used in the analysis
have the advantage that contributions from both processes to the surface
energy balance are most likely minimal.
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II EXPERIMENTAL PROCEDURES
A. Surface Observations
Although it would be desirable to obtain measures of the downwelling
irradiance at the surface simultaneously over each of the various urban
and rural surface types, it was necessary to accept a single site only.
However, for the clear conditions selected for study, a single location
should provide a representative measure of the forcing function at all
locations, except in situations with extreme variations in pollutant
loading. An Eppley Precision Spectral Pyranometer (PSP) was mounted free
of sky obstructions to measure the total direct-plus-diffuse solar
irradiance on a horizontal surface. During August 1972 this instrument
was installed at the Granite City Army Depot as part of an SRI METROMEX
experiment.2 At the same site the atmospheric radiation incident on
a horizontal surface was recorded from an Eppley Pyrgeometer Infrared
Radiometer (PIR). Nearby observations of pressure, wind velocity,
temperature, and wet bulb temperature also were available; the SRI lidar
used during METROMEX provided a relative measure of local particle loading
of the lower atmosphere. Data from other METROMEX experiments were
available for other locations in the St. Louis area.
The surface site was established at St. Louis University during a
second field program at St. Louis in April 1973. The same Eppley PSP was
used for the measurement of downwelling solar irradiance, but the
atmospheric radiation was inferred from concurrent measurements with a
C.S.I.R.O. Net Radiometer (NR). The latter instrument was installed with
a blackened dome covering its bottom sensing surface. This dome contains
a thermocouple junction; a reference thermocouple junction immersed in a
reference bath at a known temperature is used to determine the black
5
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body radiation incident on the lower surface of the NR. Thus, the
residual difference between the black body radiation and the measured
net radiation gives the downwelling irradiance only. At night, the
downwelling irradiance is simply the desired atmospheric radiation.
During the day, the separately measured total insolation (from the PSP
measurement) must be subtracted from the downwelling irradiance derived
from the NR to obtain the atmospheric radiation. A nuisance with
operation of the NR was the requirement to supply nitrogen from a tank
to maintain dry-air pressure for inflation of the upper polyethelene dome
of the instrument. Some difficulty was encountered in maintaining a
nearly constant pressure on the dome over an extended period of time
without readjustment.
Data from the PSP and PIR during August 1972 and the PSP and NR
during April 1973 were recorded on a two-channel Hewlett-Packard Moseley
recorder.
B. Aircraft Observations
The two key measurements of the program were the diurnal variations
of surface temperature and of albedo over the heterogeneous lower boundary
of the urban-rural St. Louis area. It was concluded that the only
feasible approach to the acquisition of these data was the use of a light
aircraft for repeated low-level flights (throughout the 24-hour period)
along the same flight track, thus covering the same surface features
each time. The twin-engine Aerocommander aircraft (shown in Figure 1)
owned by Colorado State University (CSU) was selected. This aircraft
had been used extensively for low-level meteorological experiments and
was equipped to acquire the type of measurements required in this study.
A daily routine of nine flights was selected for documentation of
diurnal variations. Each flight lasted approximately one hour, allowing
one-half hour for the departure leg and one-half hour for the return leg
6
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along the same track. During August, take-off times originally were
selected for 0000, 0300, 0600, 0830, 1100, 1330, 1600, 1830, and 2100 in
Central Daylight Time. Because of greater daytime variability in surface
properties flights were spaced more closely during the day than during the
night. During April, take-off times (Central Standard Time) were set
at 0100, 0400, 0630, 0900, 1130, 1400, 1630, 1900, and 2200. The flight
schedule was designed to provide maximum data density during daylight
hours when surface temperatures change most rapidly. This is particularly
important because the analysis methodology required the specification
of the diurnal variation of the meteorological parameters in terms of a
Fourier expansion.
Flight tracks were chosen to sample a variety of land-use types
and to approximately parallel the low-level wind flow; accordingly, they
were based in large part on the clear-sky wind rose climatological data
for the given times of year. Two flight levels (departure and return)
were designated at 460 m and 1220 m above the mean ground level. The
upper level, near the top of the boundary layer and the cloud-base level
(for small cumulus clouds), provided an appropriate altutude for the
aerial photography. In addition, by acquiring data at two levels, it
is possible, in principle, to infer the effects of atmospheric attenuation
on the measurements of surface temperature and albedo.
Figure 2 illustrates the flight tracks adopted for August 1972
and April 1973. These tracks were selected not only on the basis of
wind roses, but were designed to avoid the critical air space near
Lambert Field as well as some of the higher obstructions in the
southwestern portion of the city. Nevertheless, each track crossed an
interesting variety of land use patterns and visually identifiable
checkpoints. River crossings are excellent checkpoints because they are
identifiable in both the surface albedo and temperature records. River
crossings along the April track were superior to those in August because
7
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(a) AERO COMMANDER 500 B (LEFT) ALONGSIDE A CESSNA
182 SKYLANE (RIGHT)
(b) INTERIOR VIEW OF EQUIPMENT RACK IN AERO-COMMANDER
SA-2322-11
FIGURE 1 AEERO COMMANDER AIRCRAFT OF
COLORADO STATE UNIVERSITY
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of the right angle of the flight track to the rivers; when the track
slants across a river a slight drift in position alters the distance
between checkpoints. For the August 1972 flights the CSV aircraft was
operated from the Alton Municipal Airport near the northern end of the
flight track. During April 1973 the aircraft was operated from the
Spirit of St. Louis Airport near the western end of that flight track.
The checkpoints for both flight tracks that were used in the final data
reduction are illustrated in Figure 2. Also illustrated along the
August flight track are the positions for which a detailed time series
analysis of data for 9 August 1972 was performed (discussed later).
Although data were recorded in the time domain, checkpoints were used
to convert all data to the distance domain. In this way variations in
ground speed along the two legs of the flight were effectively removed
by changing the data density per unit distance. Table 1* contains a
listing of all flights conducted during the program.
Under a subcontract with Colorado State University, its pilot
and technician obtained the following measurements from the aircraft:
(1) Subtrack photographs with two Hasselblad 70 mm cameras
(2) Total downwelling solar irradiance with an Eppley Pyranometer
(3) Total upwelling solar irradiance (reflected solar radiation)
with a Yellott SOL-A-METER (solarimeter)
(4) Surface temperature with a Barnes PRT-5 radiometer (8 to 13 |j,m)
(5) Wet and dry bulb temperatures at flight altitude.
Aerial cameras were employed to document surface characterisitcs of
regions used later for time series analysis, to verify checkpoint
*
Times shown in this table are flight starting times in contrast to
the text and figures where some average time is used to designate a
specific flight.
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Flight Check Points
x Locations For Time Series Analysis
SA-2322-12
FIGURE 2 FLIGHT TRACKS, CHECK POINTS, AND LOCATIONS SELECTED
FOR HARMONIC ANALYSIS OF DATA
10
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Table 1
CHRONOLOGICAL SUMMARY OF AIRCRAFT OPERATIONS IN ST. LOUIS
DATE
9 August 1972
11 August 1972
12 August 1972
17 April 1973
START
Local Time?
0345
0555
0850
1120
1330
1600
1845
2100
0030
0330
0630
0900
1130
1400
1630
FLIGHT
TRACK t
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
N-S
1100
1400
N-S
E-W
23 April 1973
24 April 1973
27 April 1973
1630
1900
2200
0100
0400
0600
0830
1115
E-W
E-W
E-W
E-W
E-W
E-W
E-W
E-W
COMMENTS
Photographs
Aircraft malfunction; flight aborted
Photographs
Photographs
Photographs
Photographs ; rain showers along
flight track
Check flight
PRT-5 test flight
Photographs
Photographs ; extensive cloudiness
Extensive cloudiness
Photographs; rain showers developed
August times are Central Daylight Time; April times are Central Standard Time.
tSee Figure 2
11
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locations and actual tracks followed in flight, and to assist in data
interpretation as a function of time of day. Good 70 mm film trans-
parencies were obtained over most of the August flight track; selected
prints over specific areas during the flight of 9 August are presented
later. Two Hasselblad cameras were used to obtain overlapping photographs
at a 1220 m flight altitude at typical cruising speed, but complete
coverage over the 90 km track on a single flight leg required changing
film during flight. With only a single technician aboard the aircraft,
other duties normally would not allow sufficient time for changing film.
For the April 1973 flights, along the E-W track shown in Figure 2,
two additional Hasselblad cameras and an observer were added to the flight
program. No complete daytime series of observations was acquired during
the April program, although rather complete photographic coverage of the
entire E-W track was obtained during an unsuccessful flight near noon on
27 April. Despite the inferior quality of some of those prints, land-use
forms and flooded areas (especially along the western end of the track)
were clearly depicted. In general, the surface types were very similar
to those covered along the other track for the August flights.
Data from the pyranometer and solarimeter were recorded onboard on
separate Moseley strip-chart recorders. The PRT-5 radiometric measurements,
dry and wet bulb temperatures, and time were recorded on a seven-channel
PEMCO analog recorder. One of the channels was used as an event marker
to indicate overflights of checkpoints along the flight track.
Albedos were determined simply as the ratio of upwelling to down-
welling irradiance. Although the pyranometric measurements of downwelling
irradiance were associated with a time constant on the order of 15 seconds
(about 1 km travel distance), such rapid variations in the downwelling
irradiance during clear-skies were not anticipated. The time constant
for upwelling irradiance measurements, on the other hand, was on the
12
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order of milliseconds (similar to the time constant for the PRT-5 radio-
meter). For the April flights a narrow-angle (20-deg) solarimeter was
added to provide more restricted views that were more compatible with the
radiometric surface temperature scenes acquired by the PRT-5. Furthermore,
for the April program, the field of view of the PRT-5 was expanded from
4 to 20 degrees with a lens. Thus, the infrared radiometric resolution
was degraded while the spatial resolution of the reflected solar radiation
measurements was increased for compatibility.
Figure 3a shows (in relative ordinates) samples of recorded
radiometric temperature response as measured along the April flight track
under cloudy skies on 17 April (not a data run). Although the two trace
segments were not acquired simultaneously, they successfully illustrate
that the coarser resolution provides appropriate data for comparison
with solar measurements. Figure 3b provides a comparison of the narrow-
angle and wide-angle solarimeter data from a flight altitude of 460 m.
In absolute form the data from the narrow-angle solarimeter (converted to
hemispheric) appear to read lower than the wide-angle data. Because of
residual uncertainties in the calibration data, results in Figure 3b are
plotted in normalized fashion. It is apparent that the enhanced
responsiveness of the narrow-angle solarimeter makes it preferable to the
wide-angle instrument.
C. Data Processing
1. Solar Radiation
Records of the downwelling irradiance measurements at the
surface were digitized manually and instrument calibration data were
applied to the digitized data. Strip chart records of the solar
measurements aboard the aircraft were checked for quality, timing, and
zero-reference drift. Airborne strip chart speeds were maintained at
2 in/min; pyranometer data were recorded over a 10 mv amplitude range
13
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-1.0
0 5
cc
o
-1.0
CJ
z
<
o
LU
LU
tr
o
00
N -0.5
_j
<
/\
NARROW ANGLE
10
20
30 40
RANGEkm
(b)
50
60
70
SA-2322-13
FIGURE 3 VARIATIONS IN RESPONSE (a) BETWEEN 4-DEGREE AND 20-DEGREE
RADIOMETRIC MEASUREMENTS OF SURFACE TEMPERATURE AND
(b) BETWEEN WIDE-ANGLE AND NARROW-ANGLE SOLARIMETER
MEASUREMENTS OF SURFACE REFLECTANCE
14
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whereas solarimeter data were expanded to a full-scale 5 mv range.
Fifteen-second averaged samples were punched on computer cards for
processing on SRI's CDC 6400 computer. Calibration, conversion to the
9 1
units of cal cm'* min , albedo calculations, and graphing of results
were accomplished on the computer in conjunction with the CDC 280 CRT
display and microfilm system. Most difficulty was encountered with the
data plotting program. It was necessary to identify data points closest
to available checkpoints on each flight. Subsequently, the spacing of
data points between checkpoints was preset in accordance with the known
range between checkpoints. In this way it was possible to align data
from the two flight levels over the proper points in range and ensure
correspondence with data from the PEMCO recorder. The biggest difficulty
with the river crossings occurred when the flight track from one leg
strayed to the east or west of the other leg (on the August flights).
Such a drift would force the appearance in the data plots of a misplacement
in the river locations on a fixed range scale. The alternative was to
shift the river crossings to exactly the same range points with an
attendant artificial compression or expansion of data points over short
stretches. In final form the upwelling and downwelling irradiances and
the albedos along a single flight leg were plotted (using a three-point
triangular slit function) separately from those along the other flight
leg. Data from the return leg were plotted in reverse order so that
the ordinates and abscissas of both graphs matched for easy comparison.
Listings of all plotted data points were obtained also as a function
of range.
2. Surface Temperature
Data from the analog tapes from the PEMCO recorder were
digitized at a high rate at Colorado State University. Resultant
digital tapes were processed on the CDC 6400 at SRI. First, revised
digital tapes were prepared, during which time one-second averages of
15
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the digital count in each channel were computed, stored and listed.
These listings were used to screen the data and assign checkpoint
locations. During the final computer run the digital counts from the
intermediate tape were averaged over five-second intervals, converted to
volts and then to temperature, and plotted on the same abscissa (range
along flight track) used to plot the solar data. Range zero always
referred to the first checkpoint on the flight track (the northern end
for the August flights and western end for the April flights), the
extreme right side of the plot always contained data from the southern-
most (August) or easternmost (April) end of the flight track. Two
graphs were plotted for each flight, but instead of separating them
according to flight altitude (leg) as with the solar data, one graph
contained the surface temperatures measured from the PRT-5 during both
flight legs and the other graph contained the dry bulb temperature for
both flight legs. The arrangement was selected because of the usefulness
of direct comparison of temperature measurements of the same type from
different altitude. Since the surface temperatures measured from both
altitudes were expected to be extremely close in magnitude, 10°C was
added to all measurements from one flight altitude to displace the
record on the plotted graph.
The most serious data reduction problem encountered was the
zero drift on the particular PEMCO recorder used, apparently as a result
in part of inadequate warm-ap during the frequent short-duration flights.
Thus, while adequate calibration data were available for converting
voltages to temperature, it was extremely difficult to obtain a reliable
quantitative zero reference to convert digital count to voltage. During
the April 1973 flights the situation was improved by installing voltage
boxes to supply known voltages to all channels at least three times
during a flight. For the Aagust 1972 data, corrections had to be based
on post-flight laboratory displays of zero drift, apparent changes in
16
-------
river surface temperature on a given flight, and on observed back-
ground changes in the digital count on the event channel when not in
use. Deducted time-dependent changes in digital count to all channels
had to be added during the final processing stage.
17
-------
Ill METEOROLOGICAL CONDITIONS
A. 9 August 1972
During the afternoon of 8 August 1972 a weak frontal system passed
through the St. Louis area. A following period of at least 36 hours
of clear weather was anticipated. It was decided to initiate flights
at 0300 CDT on 9 August 1972; at the time light winds from the NNW
prevailed. A minimum (shelter-height) surface temperature of 15°C
occurred at about 0540 CDT. By 0900 surface winds had shifted toward the
NE. Some cirrus clouds were present in the morning and some cumulus
activity occurred in the afternoon. The flight initiated at 2100 CDT
was aborted because of an aircraft alternator malfunction. This
incident terminated the mission during what subsequently developed as
the best opportunity for a 24-hour period of observation under reasonably
steady meteorological conditions. Particle loading of the atmosphere, as
revealed by time-height displays of lidar backscatter signals, was
relatively light for the area for this time of year.
Figure 4 shows the total insolation as well as the atmospheric
infrared irradiance at the Granite City surface site on 9 August 1972.
The influence of morning cirrus clouds and small afternoon cumulus clouds
on the downwelling solar irradiance is apparent in the trace. The
maximum in the curve of atmospheric radiation occurs more than an hour
after the maximum incoming solar radiation, but the trace generally
shows little variation. An even greater phase lag was anticipated. A
careful examination of the PIR data suggested that measurements of the
atmospheric radiation were not reliable over short time scales; apparently,
the instrument responded to short-term solar heating of the instrument
window rather than solely to the true local infrared scene aloft.
19
-------
r 8
<
(fl
I
(-
H
I
o
o
o
LL
CC
CO
_l
<
o
N
IT
O
X
Q
O
< CN
Q O>
DC O
UJ D
I <
Q.
CO O)
O .
5 00
I- n
en
< t
0°
CO UJ
*r
LU
DC
CO
o
10
o
CN
O
UIU1 _LUS |E3
L ~ c~
20
-------
B. 11 August 1972
On 10 August the region of highest pressure in the area had
shifted to the southeast, enabling a return flow of warmer air with
higher humidity from the south. The forecast for 11 August called for
fair weather but with cumulus activity in the afternoon leading to
perhaps a 4/10 sky cover. Inasmuch as the flight track used on 9 August
was suitable, another series of observations was initiated with the first
flight at 0030 on 11 August. At that time surface winds were light from
the SSE. A minimum temperature of about 17.4°C was observed at 0530.
By daylight a considerable cover of cirrus clouds prevailed but, since
solar heating was evident, the mission continued. Surface winds increased
during the morning with directions shifting through S to SSW and then
to SW. At the same time the cirrus cover dissipated. The winds subsided
in the afternoon but small cumulus began forming by 1330. By 1530 winds
had become variable and considerable convective activity had increased
the cumulus cloud cover to about 5/10. The maximum temperature at the
Granite City site was 32.2°C. At 1545 CDT cumulonimbus clouds developed
nearby and extended almost overhead by 1630, the starting time of
afternoon flight. Shortly thereafter the winds at the Granite City site
shifted to the N and then the NE while remaining light. Some showers
had occurred in the city and the mission was aborted after the 1630 flight.
Figure 5 shows the total solar radiation and atmospheric infrared
radiation measured at Granite City during the daytime of 11 August. The
curve for total insolation illustrates the deterioration of the forcing
function of the surface energy balance near 1600. Although particle
loading of the atmosphere was somewhat more extensive than on 9 August
1972, 11 August was not a day with strong pollution.
21
-------
8 2
I-
I
rs <
- Q
O
o
U
LL
CC
O
N
cr.
O
Q
CJ
5 2
cc
Q. T-
CO ^
O .
< ^
CO LU
LU
DC
o
CM'
m
a
lea 3DNVIQVUHI
22
-------
C. 23 April 1973
A second experimental program in the St. Louis area was arranged
with Colorado State University to permit availability of their aircraft
during a two-week period. Unfortunately, the desired optimum weather
conditions did not prevail during this period. Unusually severe flooding
affected the general area during the stay, thus rendering somewhat
atypical the rural-urban differences in surface characteristics. No
satisfactory 24-hour periods for the observational program occurred
during the first week. During the following week the forecasting
problem became very difficult due to periodic surges of moist air aloft
with upper-level cloudiness, sometimes with light rain. As events
developed, a suitable 24-hour period would have been possible following
the rain on the night of 22 April 1973. The forecast for 23 April was
for fair weather until late in the day again. However, when it began
to appear that overcast conditions would not occur until sometime on
24 April it was possible to initiate a series of observations late in
the day of 23 April. It was concluded that at least a series of
observations during the cooling period following a dry daytime period
would be worthwhile. The first flight could not be started before 1630
CST, at which time skies were clear with relatively light winds from
the WNW. By about 0000 on 24 April cirrus clouds began moving in over
the surface site at St. Louis University. Before sunrise winds shifted
to the NE, and eventuall more to the E. By 0900 on 24 April a middle
and high overcast condition had developed and further flights were
cancelled. Inasmuch as only a very limited period of insolation was
recorded before sunset and the nighttime record of atmospheric radiation
was very steady (with only a slight increase from cirrus clouds after
midnight), these observations were not presented herein.
23
-------
IV AIRCRAFT OBSERVATIONS
A. Solar Data
Graphic records of all of the processed solar data obtained during
the flight days of 9 August and 11 August 1972 are presented in the
Appendix. Data samples illustrated in Figure 6 refer to the 1400 CDT
flight of 9 August. The origin of the range scale shown in Figure 6
corresponds to the northernmost checkpoint in Figure 2. A broad portion
of the Mississippi River was crossed at a range of about 10 km. Some
irregularities in the measured downwelling solar irradiance in Figure 6
result from clouds existing above the aircraft. The dip in downward
flux measured from the 460 m altitude at the 50 km point in range is
associated with an artificial maximum albedo; this is the result of
cloud shading the pyranometer but not the target area on the surface.
A striking feature of the illustration, which is typical of all obser-
vations, is the lower albedo over the urban area (roughly, between 33
and 45 km range) relative to the surrounding suburban and rural areas.
Although the spatial difference in albedo is only a few percent absolute,
the reduced urban albedo surely is significant in terms of the surface
energy budget. More of the solar radiation reaching the urban surface
is available for heating the surface. In addition, the lack of sig-
nificant evapotranspiration processes over the urban area means that
even more solar radiation is available for heating. A complete
explanation of the lower urban albedo requires a more careful examination,
but the observed differences are probably accounted for by the structural
"trapping" of solar radiation and shading of other surfaces in the urban
area, combined with a surprising number of relatively dark urban roofs,
areas with reflective soils outside the urban area, and an increase in
25
-------
7 2.0
0 1.0
<
Q
<
DC
^ 0.5
' I '
URBAN I
CENTER ,\ ;
ALBEDO
DOWN
UP
20
40
60
km
RANGE
(a) FLIGHT ALTITUDE = 460 METERS
80
17.5
15.0
12.5
100
1.5
1.0
tr
E 0.5
URBAN
CENTER
ALBEDO
DOWN
UP
I
20
40
60
km
RANGE
(b) FLIGHT ALTITUDE = 1220 METERS
80
17.5
15.0
12.5
100
SA-2322-17
FIGURE 6 AIRCRAFT SOLAR MEASUREMENTS, 1400 CDT FLIGHT, 9 AUGUST 1972
26
-------
reflectance over rural areas at wavelengths just beyond the visible range.
From higher altitude the albedo variations could appear more uniform,
but would depend on the scattering/absorption properties of the urban
aerosols.
Originally it was hoped to perform a detailed examination of
possible diurnal variations in albedo (as function of surface type) as
well as height variations in albedo as determined from the aircraft
observations at two altitudes. It is possible, for example, that as the
sun's elevation and azithmuth change during the day the complex changes
in shading within urban structures could result in a diurnal variation of
albedo. Both height and orientation of structures would be important.
However, other factors (including surface wetness) also are involved in
diurnal variations and the accurate repetitive measurement of small
changes in albedo is a difficult task that requires a considerable body
of data before final conclusions can be drawn.
The deduction of temporal changes in surface albedo on the basis
of aircraft observation introduces some uncertainty due to time changes
in atmospheric attenuation and turbidity. An attempt to remove this
uncertainty was accomplished by overflights of each site at two altitudes
(460 m and 1220 m) during each flight. Presumably, consistent identifiable
differences in the measured albedos could be used to adjust to an
appropriate surface albedo. Unfortunately the differences again are
small and are subject to factors other than atmospheric attenuation.
Thus the periodic observations from the two flight altutudes failed to
establish any significant height or time variations (very low sun angles
excluded) of surface albedo. Only the horizontal variations were
significant and were related to variations in reflected solar radiation.
Time differences in the overflight of a given portion of the track
by a single aircraft at two altitudes complicates the interpretation of
27
-------
changes in measured solar radiation. Along the near end of the track,
overflight at the second altitude may occur as much as 50 minutes later;
the time delay is much shorter at the far end of the track. During this
period of delay, time changes in the downwelling solar radiation (and
possibly the albedo) occur regardless of atmospheric changes. With any
cloudiness aloft, changes in cloud locations and in the cloud shadow
location will influence the relative solar measurements over a given
site. Furthermore, the actual scene being viewed changes with aircraft
altitude. As the altitude is increased the viewed area increases rapidly
and the type of surface viewed is changed by an amount dependent on the
homogeneity of the surface. In addition, even the same objects in
the field of view are not viewed at the same sun angles, except at the
jt
subpoint, and differences in shading occur. How these factors influence
the deduced atmospheric attenuation during the course of the day may be
difficult to infer unless experiments are first conducted over a truly
homogeneous surface of sufficient size to fill the field of view at
both flight altitudes.
Although the observed relative spatial variations in albedo were
real, absolute values may have been biased by calibration inaccuracies.
Comparisons of surface and aircraft measurements of incident solar
radiation indicated that the downwelling irradiance interpreted from
aircraft measurements was too large. Assuming the validity of upwelling
irradiance measurements on the aircraft, the absolute magnitudes of
calculated albedos apparently were too small.
Figure 7 illustrates the downwelling irradiance measurements on
11 August 1972 at flight altitudes of 460 m and 1220 m. Differences in
the measurements over urban and rural locations were insignificant during
the time period illustrated. The indicated maxima in incident solar
Subpoint refers here to the point on the ground directly beneath the aircraft,
28
-------
1220 m FLIGHT ALTITUDE
460 m FLIGHT ALTITUDE
10
11 12
CDT hours
13 14
SA-2322-18
FIGURE 7 HEIGHT VARIATIONS OF MEASURED INCIDENT SOLAR
RADIATION, 11 AUGUST 1972
29
-------
radiation measured at 1220 m and at 460 m are 1.76 and 1.66 cal cm 2
min"-1-, respectively. The maximum incident solar radiation measured at
the surface (at the Granite City site) was only about 1.3 cal cm~2 min"1.
If it is assumed that complete homogeneity existed in the atmosphere
below 1220 m and that the surface measurement was correct, then it must
be concluded the absolute magnitudes of the aircraft measurements were
overestimated by about 20%. If, in addition, the aircraft solarimeter
measurements were assumed to be accurate, then the inferred albedos
should be increased by about 25%. Relative differences, which are small,
would be increased by the same amount.
Even with residual uncertainties in absolute magnitudes of solar
components it is possible to examine relative variations in terms of
ratios of departures from average to average. Data from both legs of
the 1700 CST flight on 23 April 1973 are presented in such nondimensional
ratios in Figure 8 for downwelling and upwelling irradiances and the
inferred albedo. Only wide-angle solarimeter data were analyzed for
presentation in Figure 8. The first leg (eastbound) of the flight was
flown at an altitude of 460 m; a loss of pyranometer data occurred during
this leg. Despite the data dropout, the decline in the normalized curve
for the downwelling irradiance clearly reveals the reduction in incident
radiation with decreasing solar elevation during the 22 minutes of flight.
On the return leg (westbound) at an altitude of 1220 m, the decreasing
solar elevation results in minimum incident radiation at the zero range
on the flight track. The influence of small clouds is most evident in
the traces for the 460 m flight; although the downwelling irradiance is
reduced by the clouds the underlying surface is not shaded simultaneously
so that albedo maxima result. Flooding of areas surrounding St. Louis,
especially at the western end of the flight track, reduced the albedo
but an albedo minimum is apparent again over the urban area. In general,
the surface albedo ranges from about 10% below average to 10% above average.
30
-------
1.5
Z
m 1 0
LU
oc
3 0.5
LU
DC
O
C/J
£ - 0.5
N
<
DC
O
Z
- 1.5
0
A: ALBEDO
i * jX
-- 1 ^ ' * x "v * * s
:"' ""'-
_ _
D: DOWNWARD FLUX
'""^11 i i 1.1 J
L \A^ ~~ .
_
f^.' ^"^^ ^ ..-'N _
U: UPWARD FLUX
I.I, .1.1.1.1
10 20 30 40 50 60 70
RANGE km
(A - A)
A
(D - D)
D
(U - U)
U
1.0
- 1.0
FLIGHT ALTITUDE = 460 METERS
1.5
CO
Z
LU
5 1.0
LU
DC
D
< 0.5
LU
2
< 0
0
2 - 0.5
N
CC
O
Z
- 1.5
C
I ' I ' I ' I ' I ' I ' I
A: ALBEDO
' " ** *. «
.' "*---*...--'' " ""-' "-' x---.-
.
D: DOWNWARD FLUX
. N ^^^^
: ^~
U UPWARD FLUX
/ ~ "" ~
i
I . I , I , I , I . I > I
10 20 30 40 50 60 70
RANGE km
(A - A) + , n
A
(D - D)
D
-------
B. Surface Temperature
The measurement of surface temperature with the PRT-5 radiometer
also was accomplished at the two flight altitudes. In principle, with
proper allowance for actual time changes in surface temperatue during
the overflights at two altitudes, the affect of atmospheric attenuation
on the measured surface temperatue can be inferred from the difference
observed from the two flight levels. However, the same factors that
influence the albedo measurements at different heights also complicate
the interpretation of temperature differences for the same site. Surface
temperatures are strongly influenced by changes in solar heating; rapid
fluctuations associated with shadows of cumulus clouds are much larger
than differences of radiometric temperature associated with atmospheric
attenuation. Of course, surface inhomogeneities contribute to variability
in the PRT-5 records; nevertheless, the general picture that emerges is
consistent with albedo measurements and expectations. Urban centers
show higher temperature than the surrounding rural areas, as illustrated
in the sample shown in Figure 9. Because of the small differences in
radiometric surface temperature with flight altitude, the data from the
1220 m altitude have been displaced upward 10°C on the graph. Summaries
of temperatures at selected sites along the track for each flight time
were used in the time-series analyses discussed below.
Figure 10 illustrates the departures of the PRT-5 measurements of
surface temperature from their means during each leg of the 1700 CST
flight on 23 April 1973. The 460 m flight altitude (flown first) was
associated with an apparent average surface temperature 1.6°C warmer
than that for the 1220 m flight altitude. Consequently, the flooded area
around the Missouri River (see flight track in Fig. 2), represented by
the broad minimum near the origin of the track, appears with a larger
temperature departure from normal in the 460 m flight record than in the
1220 m flight record. The same is true for the sharp minimum characterizing
32
-------
50
40
in
CC
30
IT
ill
a.
u
t-
o
<
u.
cc
D
OT
I-
flC
a.
20
10
URBAN I
Measured From 460 Meters Altitude
Measured From 1220 Meters Altitude, 10°C Added
I I I I !
20
40 60
RANGEkm
80
100
SA-2322-20
FIGURE 9 AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE MEASUREMENTS,
1400 CDT FLIGHT, 9 AUGUST 1972
33
-------
o
O
oc
UJ
(T
D
UJ
Q
UJ
QC
D
H
<
DC
HI
Q.
UJ
H
I-
CE
Q.
Flight Altitude 460 Meters
Flight Altitude 1220 Meters
- 5.4 -
FIGURE 10 NORMALIZED AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE
MEASUREMENTS, 1700 CST FLIGHT, 23 APRIL 1973
34
-------
the crossing of the Mississippi River near the center of the track.
These results are reasonable since water body temperatures remain
relatively uniform over short time intervals due to the large specific
heat and effective mixing depth of the water. Thus, after accounting
for the time change of the normal temperature for each track, the water
temperatures measured from both altitudes differ by less than one degree
and indicate that the atmospheric influence on the measurements was
small at those localities. The temperature departures above normal are
restricted to the urban area, which is significantly warmer than the
rural areas to the east. Records from the two flight altitudes are in
excellent agreement except for an unspecified feature in the western
portion of the urban area.
Apparent spatial variations of the radiometric surface temperature
could be influenced by marked gradients in surface emissivity (in the
10 to 12 |j,in spectral region) or by significant variations in atmospheric
attenuation. No evidence is available to support a significant emissivity
variation that accounts for observed horizontal temperature differences.
Some insight into the possibility of differential atmospheric attenuation
is provided by the airborne PRT-5 measurements from two altitudes.
Data acquired on 9 August 1972 were averaged over two segments
of flight track representative of urban and rural surfaces. Results
for the two flight altitudes are illustrated in Figure lla, where smooth
curves have been drawn through data points derived from seven flights.
The pronounced daytime increase of the urban surface temperature relative
to the rural surface temperature is clearly depicted. In all observations,
the surface temperatures measured from the lowest altitude exceed those
measured from the highest flight altitude, as anticipated by the presence
of atmospheric attenuation. Only for the 1400 CDT flight does the urban
temperature difference with flight altitude significantly exceed the
35
-------
LU
CJ CJ
DC
D
in
DC (-
H <
IJJ DC
5 LU
40
35
30
25
20
15
10
5
^** ^" *^ Flight Altitude 460 Meters
Flight Altitude 1220 Meters
URBAN
AREA
0400 0600 0800 1000 1200 1400
CDT hours
(a) 9 AUGUST 1972
1600
1800
2000
LU
CJ CJ
30
25
LL
DC
to LU 20
DC h-
H <
UJ CC
5 LU
21
Q £
< h-
tr
15
10
I I I I I
^? TZ !^ Flight Altitude 460 Meters
Flight Altitude 1220 Meters
RURAL
AREA
1800
2000 2200 0000
CDT hours
(b) 23-24 APRIL 1973
0200
0400
FIGURE 11
SA-2322-22
URBAN AND RURAL SURFACE TEMPERATURE VARIATIONS WITH TIME
-------
rural difference. This suggests either greater attention in the urban
atmosphere than in the rural atmosphere at 1400 CDT, with a suppression
of the urban-rural surface temperature contrasts, or reduced attenuation
below 460 m over the urban area at this time. (The same feature was
not apparent at 1400 CDT on 11 August 1972.)
For the evening and night hours of 23 April 1973, PRT-5 data along
the second flight track also were averaged over urban and rural areas.
Results illustrated in Figure lib show slightly more atmospheric
attenuation over the urban area throughout the period. Presumably, the
excess of urban surface temperatures over the rural surface temperatures
should have been larger than those measured from the lowest flight
altitude. Unfortunately, no data were available on differences in
particle loading of the atmosphere over the two areas.
C. Air Temperature
Included in the aircraft observations were the air temperatures
along the two flight altitudes. These data, although not specifically
required for the surface analysis, are significant for several reasons.
First, they provide a quick graphic display of thermal stability or
changes in stability along the flight track. Second, harmonic analysis
may be used to examine differences in the vertical exchange of sensible
heat in the boundary layer. Finally, they are useful in assessment of
atmospheric absorption and emission of infrared radiation, especially
when combined with humidity measurements.
Samples of air temperature measurements at the two flight altitudes
are shown in Figure 12; other data are included in the data summaries
presented in the Appendix. The horizontal profiles of air temperature
are sensitive to the relative accuracy of the measurements, to slight
changes in flight altitude, and to the possibility of differential
37
-------
25
20
LU
DC
cc
til
Q.
uj
DC
15
10
460 METERS ALTITUDE
1220 METERS ALTITUDE
20
40 60
RANGE km
80
100
SA-2322-23
FIGURE 12 AIRCRAFT AIR TEMPERATURE MEASUREMENTS, 1400 CDT FLIGHT,
9 AUGUST 1972
38
-------
advection along the tracks. Differences in the stability over urban
and rural areas during different times of the day are of special interest,
but often small in magnitude above the surface layer. The pronounced
influence of convection on the temperature differences at the two flight
levels is illustrated by the relatively large temperature differences
in Figure 12. On many of the records slight changes in temperature with
time (during the period of flight) are noticable. On the other hand,
spikes that appear in the reduced air temperature data represent noise.
39
-------
V CLIMATONOMICAL ANALYSIS
A. Climatonomy Theory
Professor Heinz Lettau was prompted in 1954 to coin the term
climatonomy in order to emphasize quantitative aspects of the subject
and to avoid misconceptions that might be associated with the word
climatology. The distinction is intended as an analogy to the development
of modern astronomy from the earlier astrology. Thus climatonomy denotes
the use of numerical models to solve the local surface energy budget
equation. A synopsis of climatonomy theory is presented below. Surface
energy budget theory expresses the principle of the conservation of
energy in the partitioning of the effective insolation at the earth-air
interface. For the case of local homogeneity, the surface energy budget
is given by
F0 = LW0T - LWol + S0 + Q0 + E0 + Po, (1)
where,
F = solar forcing function (cal cm~2 min~^); the effective short-
wave radiation at the surface,
LWO| = upwelling longwave radiation at the surface
LW0i = downwelling longwave radiation at the surface
So = subsurface heat flux density
Q0 = atmospheric heat flux density
E0 = evaporative heat flux density
P0 = photosynthetic heat flux density.
By definition, heat flux away from the surface is defined as a positive
flux. For the urban surface, photosynthetic energy transforms can
usually be ignored, while on the overall average they may account for
41
-------
5% to 10% of the available solar energy (Van Wijk) .3 In this exploratory
study we have chosen to ignore this term, although further work should
seek to evaluate this impact of vegetation on rural-urban climatic
differences.
In climatonomy, the energy budget is examined over basic meteoro-
logical periods (e.g., diurnal and annual) through the use of "Fourier
synthesis." Thus each term in Eq. (1) is represented by a mean value
and harmonics. Expanding each term in Eq. (1) we obtain
m
Fo = Fo +£1 V'o cos >
(2a)
m *
LW0| = LW0| + E A.jLW0t cos (int - 6. + y. )> (2b)
i=i i i
m
LWn| = LW I + T, A LW | cos (int - 6 + 3 ), (2c)
0 ° i=l i o i i
_ m
S = S + £ A S cos (int - 6 + ilr ) , (2d)
o o i=i i o i i
Q = Q + £ A Q cos (int - 6 + cp ) , (2e)
o o i=i i o i i
_ m
E = E + Z A E cos (int - 6 + V *) , (2f)
o o i=i lo i i
where t is time, i is the harmonic order, and n is the basic frequency
when n = 2n/T and T is the basic period (i.e., one day). In Eq . (2),
A.O is the amplitude of the ith harmonic, 6. is the phase angle for the
ith harmonic of the forcing function, and (). is the phase lag of the
various response functions to the solar phase. In the analyses that
follow, zero time reference corresponds to midnight. As usual, the
overbar denotes the time-averaged value over the basic period.
A basic premise of climatonomy is that the primary response to the
solar forcing function is the surface temperature, and that the "climatic'
functions are secondary responses, via the surface temperature, to the
solar forcing function. In other words, each of the climatic functions
42
-------
can be expressed in terms of surface temperature and hence Eq. (l) may
be solved to yield a unique set of mean values plus variation of the
response terms. It is thus appropriate to first introduce the Fourier
representation for the surface temperature and then to rewrite the
secondary response functions in terms of surface temperature, where
m .,
T = T + E A T cos (int - 6 *) . and (3a)
o o i=i i o i
. m
T = T + E (A.F /Z.) cos (int - 6 - £.), (3b)
o o i=i 101 i i
where,
Z = A F /A T , and (4a)
i i o i o
C. = \* - 5.- <4b)
Furthermore,
m
Lwt=LWt+ E (TAT) cos (int - 6 - r + v ), (5a)
o o i=i i i o i i i
m
LW I = LW i + E (BAT) cos (int - 5 - C + P ), (5b)
o o i=i i i o i i i
m
S = S +E (VAT) cos (int - 8 - C + A ), (5c)
o o i=l i i o i i i
m
Q = Q + E ($ A T ) cos (int - 6 - £ + cp ), (5d)
o o i=i i i o i i i
m
E =E + E (XAT) cos (int - 5 - t + y ), (5e)
o o i=l i i o iii
where the following identities are introduced
ALWf = rA.T,Y* = -C+Y; (6a)
i o1 110 i 11
I Ao*-r
AS=TAT,\j;* = -r+il;; (6c)
io iio i i i
43
-------
A.Q = $.A.T , cp.* = - £ + cp ; (6d)
10 110 i i i
A.E = X.A.T , X.* = - t. + X. (6e)
10 110 i 'i i
Introducing the identity (4a), Eq. (2a) is rewritten as
m
F = F + 7 (Z A T ) cos (int - 6 ). (7)
o o i=i i i o i
Lettau then introduces Eqs. (5) and (7) into (1), and expands the
cosine functions in terms of cosine and sine terms through the trigon-
ometric identity:
cos (int-S -C +x ) = cos(int-5 )cos(f -x ) + sin(int-6 )sin(C -x ).
i "i i i'ii ill
The basic cycle average equation is subtracted, leaving only a departure
equation that is evaluated at int = 6 and int =6 + n/2 to yield two
i i
simultaneous, independent equations, where:
-B sing + r sinv + ^f simlf + $ sin + X sinv
.. i i i i i i i i i i . _N
tan C, = (8)
' i -B cosg + J cosy + 1' cosijf + $ cos^> + X cosx
and
, Z. = -B. cos(£.-|3_.) + r_cos(C.-Y.) + 1P. c°s( C .-^ . )
+ § cos(C -co ) + X cos(C -X )
i "i i i i i
In regard to the St. Louis experimental program, it is important
to recall that not all of the amplitude and phase terms are obtainable
directly from the observations, and hence we need to consider the
parameterization of these terms on the basis of identifiable surface
features.
Parameterization of the upwelling infrared flux at the surface is
straightforward through application of the Stefan-Boltzmann law,
LW T = eoT 4, (10)
o o
44
-------
where e is the surface emissivity and a is the universal Stefan-Boltzmann
constant (0.813 X 10~7 mly min'1 °K~4). Upon introducing Eq. (10) into
Eq. (3a) and solving for the partial impedance and phase, we obtain
r sr 4 LW T/T , and (lla)
1 O O
Y. = 0. (lib)
The partial impedance B. and phase fj for the downwelling longwave flux
at the surface have not been parameterized here as they were obtained
through Fourier analysis of the continuous diurnal pyrgeometer measurements
made at the ground station. Parameterization is possible through a wide
variety of empirical and theoretical approaches, such as the use of the
Angstrom ratio or Swinbank's method4 as discussed by Dabberdt5 , to
mention only two.
The subsurface heat flux density is parameterized through the
application of Fourier's law of heat conduction--Eq . (12a) and the
continuity equation for heat in the absence of sources and sinks Eq .
(12b), where
X 8T
S = - , and (12a)
dz
Here A. is the thermal conductivity (cal cm"1 °K min"1) and C the
volumetric heat capacity (cal °K~1 cm"3) of the submedium. Considering
the medium as a homogeneous conductor (dA/dz = dc/dz = 0) with time-
independent thermal coefficients OX/dt = dC/dt = 0), the partial
impedance T and phase il; are given as
i i
1/2 1/2
^ = UCin) = n(in) ' , and (12c)
1)1. = n/4, (12d)
45
-------
where ^ (cal °K~1 cm" sec ~-L/2) is defined as the thermal admittance.
Parameterization of the atmospheric heat flux density is perhaps
the most difficult. Lettau presents a type of similarity approach
based on the near-surface vertical profile of potential temperature.
Both the partial impedance <[? and the phase cp are given in terms of a
i i
characteristic number N. that is a unique function of the frequency,
W
aerodynamic surface roughness z , and the mean friction velocity V ,
o
where
The partial impedance §. is then expressed as
pC V*
$i = (a+bN )(l-lT>. (14a)
i
The term M expresses the magnitude of convective mixing relative to
3T
mechanical turbulence; its absolute value is proportional to Q~~/V and
o
is less than unity, and its sign is determined by that of Q . For urban
5JT
areas, V will usually be large because of the tall roughness elements
#
and hence M will be small. Upon assuming bouyancy effects on turbulent
diffusion of heat as small in comparison with mechanical mixing, diurnal
variations of M* are similarly small [(T/iM*)dM*/dt = 0] and Eq. (14a)
can be simplified accordingly, where
pC V*
(14b)
Lettau also gives an expression for the phase lag,
cPj = tan-l[2 ) (I4c)
p = tan * I I
i ^a+bNi f
where a, b, and c are semi-empirical constants.
46
-------
Since it would have been impractical if not impossible to directly
u.
determine V and zo along the flight path, these also must be estimated.
Values for z were derived from an empirical relationship developed by
Kung,6
log z = -1.24 + 1.19 log h*, (15a)
10 o
where h* is the characteristic physical height of the roughness elements.
The term V* is, in turn, also derived from an empirical equation from
Kung based on the relationship between the geostrophic drag coefficient
C and the surface Rossby number Ro,
C = V*/V = 0.174/(log10Ro - 0.81) (15b)
Ro = V /z0f> (15c)
where V is the geostrophic wind and f the Coriolis parameter.
g
In this study a simplistic approach toward the parameterization of
evaporation has been taken with E expressed in terms of Q using the
o o
inverse Bowen ratio Bo. Thus,
X = Bo$., and (16a)
In the following section the reduction of the observations is
discussed in terms of the input requirements of the theory as well as
its application for the evaluation of the evaporative and thermal
properties of the surface throughout the region.
B . Method of Approach
Upon examining all the data collected during the August 1972 and
April 1973 experimental periods, it was decided to analyze in detail only
those data from 9 August. This decision was based upon one very basic
47
-------
and important criterion: the theory as outlined earlier is only strictly
applicable when the basic (diurnal) cycle is controlled by the surface
features, and hence one should avoid periods having significant diurnal
trends and of course abrupt changes in the mesoscale atmospheric structure.
Only the 9 August data satisfied this requirement.
In review, five basic types of meteorological data obtained on a
diurnal basis were available for climatonomical analysis:
Downwelling longwave radiation at the surface station
Downwelling solar radiation at the surface station
Downwelling solar radiation at each of two altitudes from the
aircraft
Upwelling solar radiation at each of two altitudes from the
aircraft
Upwelling window-channel infrared emission (in terms of equivalent
blackbody temperature) at each of the two aircraft altitudes.
In addition, available supplemental data sources included:
Twice-daily boundary layer wind and temperature profiles from
the NWS EMSU station located at the Gateway Arch
Aerial photographs obtained along the flight path by the aircraft.
While the aircraft observations were made continuously along both
of the two 90 km segments of each flight, it is desirable to isolate
portions of the flight track corresponding to distinctly different yet
individually homogeneous surface types and to thus obtain average
meteorological conditions representative of each. Figures 13 through
21 are aerial photographs of each of the nine surface sites (see Fig. 2);
Table 2 identifies the various sites and briefly describes each. It was
considered desirable to choose rural sites on opposite sides of the
urban core so as to examine possible skewness in the climatic distribution
48
-------
that might arise from advection associated with the urban heat island.
The sites were carefully evaluated to ensure reasonable homogeneity
over a scale of several kilometers, thus minimizing the impact of
discontinuities in land use. Digitized records of the hemispheric
solar radiation measurements from the aircraft were averaged over 15-sec
periods while 5-sec averages were obtained for the higher-resolution
infrared radiometer measurements of surface temperature. Summaries of
these data over the various sites were used in the analysis of the
surface energy budget.
The reduction of the surface observations of downwelling longwave
and solar radiation in terms of the requirements of the theoryEqs. (2a)
and (2c)--is quite straightforward and involves only the direct application
of harmonic analysis (see for example, Panofsky and Brier). Upon
recalling Eq. (2a) and expressing the absorbed solar radiation at the
surface (i.e., the surface forcing function) in terms of the insolation
F I and the surface albedo a, we obtain
o
F = FI-Ft=Fj. (1-a) = (17)
oo oo
r m i
(l-a) F | + £ A.F |cos(int-6.) ,
|_ o i=i 10 i J
when the albedo is time-independent. Because the 9 August measurements
entail solar data on only five of the flights and because these were
obtained well above the surface, these aircraft observations were utilized
only to determine the albedo of each of the nine representative surface
types; the insolation measured at the surface station is used in the
evaluation of Eq. (17) under the assumption that spatial variations of
F I along the flight track were negligible on this day. Values at 30-min
o
intervals were taken from the analog trace, and the amplitude and phase
terms were computed for 24 harmonics; the results are summarized in
Table 3. Only the first and second harmonics are listed as together they
account for 98,8% of the total variance.
49
-------
FIGURE 13 SITE R-1
FIGURE 14 SITE R-2
FIGURE 15 SITE R-3
FIGURE 16 SITE R-4
50
-------
FIGURE 17 SITE R-5
FIGURE 18 SITE R-6
FIGURE 19 SITE R-7
FIGURE 20 SITE R-8
51
-------
FIGURE 21 SITE R-9
52
-------
Table 2
DESCRIPTION OF SURFACE AREAS SELECTED FOR ANALYSIS
Site Description Range (km)t
R-l Mostly farmland; roadway; 23.8N
some trees
R-2 Mostly woods, some fields; 19.9N
roadways
R-3 New suburban housing tract 13.ON
R-4 Commercial-industrial; 7.8N
old residential
R-5 Old urban residential 3.7N
R-6 Old urban residential; 3.7S
some light commercial
R-7 Farmland 12.5S
R-8 Mostly woods and fields; 23.8S
some farmland
R-9 Mostly woods, some fields 33.7S
*Locations shown in Figure 2
tDistance (north or south) of city center
53
-------
The downwelling infrared flux density as recorded at the surface
station was also assumed representative of conditions at each of the
nine sites. As above, the harmonic analysis of values at 30-min intervals
was performed in the evaluation of Eq. (2c); the results are also listed
in Table 3. In general agreement with the solar data, 95.6% of the
variance is specified by the first and second harmonics.
Table 3
RESULTS OF HARMONIC ANALYSIS OF 9 AUGUST 1972 SURFACE
OBSERVATIONS OF DOWNWELLING SHORT- AND LONGWAVE
RADIATION AT GRANITE CITY, ILLINOIS
Parameter Mean i=l i=2
F I (ly/min) 0.428
o
A F I (ly/min) 0.646 0.235
i o
6. (rad) 3.429 0.555
LW | (ly/min) 0.515
o
A LW J, (ly/min) 0.060 0.019
i o
(3*. (rad) - 0.305 - 0.405
Determination of a daily average and the harmonics for the aircraft
observations cannot be obtained through standard harmonic analysis due
to the irregular spacing of the seven averaged data points representative
of each surface region as measured at each of the two altitudes. Further-
more, the small number of data points, and hence relatively large time
intervals, prevented the use of extrapolation methods. Hence we evaluated
the applicability of a nonlinear regression routine available at the
Institute. In this manner we specified the form of the Fourier series
54
-------
and obtained the mean, amplitude, and phase that best fit the data. A
two-harmonic function was chosen, resulting in a five-parameter fit
to the data:
G(t) = R + R cos(0.2618t-R ) + R cos(0.5236t-R ), (18)
12 34 5
where,
R = average value over the period (°C)
R = amplitude of 1st harmonic (°C)
2
R = phase of 1st harmonic (rad)
O
R = amplitude of 2nd harmonic (°C)
4
R = phase of 2nd harmonic (rad).
o
The form of the equation is directly analagous to that of Eqs. (2a)
through (2f). Prior to applying the method to the reduction of the
aircraft data, the method was first applied in several test cases to
evaluate its validity. As a simple first trial, 14 irregularly spaced
points along a pure cosine wave with origin at 00 hours were analyzed
using a three-harmonic form of Eq. (18). The regression method requires
initial guesses (R*j) of each parameter; these were purposely chosen
poorly: R * = 0.9, R * = 0.1; R * = 0.15 rad, R * = 0.2, R * = 0.5 rad,
_L ^ o 45
R * = 0.2, and R * = 0.5 rad. In spite of the "bad" initial values,
6 7
the routine converged rapidly to provide the following results: R =
1.2 X 10~4, R = 1.000, R = - 0.9 X 10~5 rad, R = 2.2 X 10~4, R =
2 3 4 5
0.6 rad, R = 1.6 X 10~4, and R =7.3 rad. Although a good test of
6 7
the method's validity in simulating a harmonic analysis, a more realistic
evaluation entails the use of observed diurnal near-surface temperatures
under essentially stationary conditions. Meteorological conditions on 9
August in the St. Louis area satisfied this criterion. Thermograph data
55
-------
for this period were obtained from seven instrument shelters in the area
(see Fig. 22) of our operations; the shelters were maintained by the
Illinois State Water Survey (ISWS) as a part of Project METROMEX.8
These strip chart data were reduced to provide 24-hourly temperature
values at each station and then analyzed using both the conventional
harmonic analysis method for all 24 values and the regression method with
only eight values. Data points chosen at times corresponding to the
times of the seven aircraft flights plus an additional value at midnight.
The results of the two sets of analyses are summarized in Table 4.
Comparison of the two methods shows that results obtained from the
regression method for all seven cases are in excellent agreement with
those of the harmonic analysis for both the mean values and the first
harmonics while the second harmonic values agree quite satisfactorily.
In all cases, the "computed" (i.e., regression method) diurnal
average temperature is within 0.2°C of the "observed" (i.e., harmonic
analysis) and the root-mean-square-difference (RMSD) is only about 0.1°C.
The computed amplitudes of the first harmonic are all within 7,6% of the
observed, while the RMSD is 4.3% of the observed mean; four of the seven
stations show agreement within 0.06 rad (15 min in time) between computed
and observed phase lags in the first harmonic, while the differences in
the other three range from 0.14 to 0.23 rad ( 35 to 60 min). Agreement
among the amplitude and phase terms is less consistent in the second
harmonic, although still encouraging. Five of the amplitude terms agree
within 0.2°C or about 30%, although two differ by up to 0.4°C; similarly,
most phase terms are within 0.4 rad (about 45 min) except two that differ
up to 1 rad. However, the overall agreement is good as the first harmonic
explains over 95% of the total variance.
As a result of these tests, the regression method was applied for
the analysis of the effective surface temperature data obtained from the
aircraft PRT-5 measurements. To evaluate this application, the seven
56
-------
PMQ
-f- Wind
^ Temperature and
Humidity
Data Used From
These Sites
SA-2322-37
FIGURE 22 NEAR-SURFACE METEOROLOGICAL STATIONS OPERATED BY ILLINOIS STATE
WATER SURVEY, AUGUST 1972
57
-------
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58
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space-averaged temperatures obtained from the upper altitude for site
R-l were analyzed first ; the resulting five-parameter fit is illustrated
in Figure 23. The fitted curve looks quite reasonable for the daytime
period, but the nighttime portion is unrepresentative in comparison
with the shape of the near-surface ambient temperature curves for the
seven ISWS stations; the fitted ambient temperature curve for station
number 022 is also shown in the figure. The discrepancy undoubtedly
resulted from the large time interval between the last evening datum
and the first morning value. The importance of one or more measurements
during this period was anticipated, but as noted earlier we were unable
to obtain these due to mechanical failure of the aircraft. In lieu of
an intermediate measurement, we estimated a reasonable value in order
to inhibit dominance of the nighttime regime by the second harmonic, as
illustrated in Figure 23. The interpolation is necessarily subjective,
although consistent among sites: a value (Tj^) is obtained midway
between the 2000 and 0400 CDT measurements by assuming that 60% of the
surface cooling occurs during the first half of the interval. This
rate reflects nighttime surface cooling typical of cloud-free conditions
as experienced during the experimental period. The temperature change
over this interval ranged on the order of 10°C at the nine sites. It
is felt that the magnitude of the uncertainty of the interpolated value
is on the order of 1°C . An error analysis was then made to evaluate
the impact of the upper level PRT-5 data for site R-l and to vary the
magnitude of the interpolated value over 0.5°C increments through ±2°C.
The rate of change with temperature in each of the parameters of the
regression analysis was essentially constant, where
AT
= 0.20,
AT
INT
= - 0.22,
59
-------
30
» V
\ AIRCRAFT, PRT-5 /
SITE R-1
0
0000
1200
CENTRAL DAYLIGHT TIME
FIGURE 23 COMPARISON OF TWO-HARMONIC TEMPERATURE WAVE AT STATION 022
AND TWO-HARMONIC REGRESSION ANALYSIS FOR SITE R-1 USING SEVEN
DATA POINTS
60
-------
AT
INT
=0.03 rad/°C,
'
A[A T]
= 0.26.
AT '
INT
A5 *
= - 0.04 rad/°C.
ATINT
In view of relatively small impact of "errors" as large as 1°C we feel
confident in the representativeness of the regression analysis employing
the single interpolated value. Certainly the resultant diurnal curve is
more consistent with both the near-surface ambient conditions and what
one would expect on the basis of the meteorological state. Figure 24
illustrates the five-parameter (two-harmonic) fit for the PRT-5 data at
each of the two levels for the nine surface sites; Table 6 in the next
section lists the mean, amplitude and phase values.
C. Application and Results
In view of the available experimental data and the basic objective
of the study to evaluate effective surface geophysical features, the
specific aim of the analysis program was to determine the feasibility
of obtaining the thermal (i.e., thermal admittance) and evaporative
(inverse Bowen ratio) descriptors of a variety of land-use types through
the application of climatonomic theory to direct and remote observations.
The first step in the analysis is the procedure to specify the solar
forcing function at each of the sites and then the primary response
function (i.e., surface temperature); through parameterization, the
secondary responses are specified or evaluated, and then the descriptors
are determined.
61
-------
30
J
25
J 20
'
D
( 15
j
; 10
]
5
30
> 25
20
J
5
1 | 1 1 1 1 [ 1 1 1 1
SITE: R1 , * .
ALT: 1220 m *
9.
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SITE: R1 . * ,.
ALT: 460 m ,.
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15 h. / "-->
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r ' .' i
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30
r- "' -I
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- ALT: 460 m ±
X \ 1 25 ^ / > -j
1- / -. ~\ I
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r- '
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15
10
R
~. ' ""
'-. u
*--.-'
-
i i i i i i i
0000 0600 1200 1800
CDT hours
2400 0000 0600 1200 1800 2400
CDT hours
SA-2322-10A
FIGURE 24 EFFECTIVE SURFACE RADIATIVE TEMPERATURE FROM TWO AIRCRAFT
ALTITUDES AT NINE SITES ON 9 AUGUST 1972
Curve is from 2-harmonic regression analysis
62
-------
35
OD
0 30
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1 25
LU
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4
''-/'
''---i
II II' 111
0000 0600 1200 1800 2400 0000 0600 1200 1800 240
CDT hours
CDT hours
SA-2322-10B
FIGURE 24 EFFECTIVE SURFACE RADIATIVE TEMPERATURE FROM TWO AIRCRAFT
ALTITUDES AT NINE SITES ON 9 AUGUST 1972
Curve is from 2-harmomc regression analysis (Continued)
63
-------
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- ALT. 460 m . ,
/' *
-
'-.. -
_ / 4
'-.*
I I I I 1 1 I I I I I
0000 0600 1200 1800 2400 0000
CDT hours
0600 1200 1800 2400
CDT hours
SA-2322-10C
FIGURE 24 EFFECTIVE SURFACE RADIATIVE TEMPERATURE FROM TWO AIRCRAFT
ALTITUDES AT NINE SITES ON 9 AUGUST 1972
Curve is from 2-harmonic regression analysis (Concluded)
64
-------
Table 3 listed the mean, amplitude, and phase terms for the
insolation on 9 August. The surface reflectivity then determines the
form of the forcing function at each site. Table 5 lists the albedo
values observed at each site for all of the daytime flights on 9 August.
In Table 6, the albedo and forcing function are summarized according
to site and aircraft altitude; for convenience, the downwelling longwave
flux given earler in Table 2 is also summarized in Table 6.
The diurnal surface temperature variations discussed earlier and
illustrated in Figure 24 are the effective surface radiative temperature
values deduced from the aircraft bolometer measurements and an assumed
constant surface emissivity of unity. To obtain some insight into the
magnitude of possible variations in surface emissivity (e), we evaluated
relative e-variations among the nine sites by assuming that the actual
mean surface temperature was indeed the same for all sites. Thus
differences in the effective mean surface temperatures are essentially
attributable to variations in the emissivity. Using the upper level
measurements first, it was found that the relative e-variations are on
the order of 7%; the largest e-values are associated with the more
urbanized sites. The lower level data resulted in similar findings with
relative e-variations less than 9%. The possible error introduced by
assuming s = 1 in the climatonomic determination of F and A T (and
i i o
subsequently, the other second order responses) is minimal; thus, for
the lack of an objective determination of absolute emissivity at the
various sites, the unity value has been used throughout. The mean,
amplitude, and phase terms for the primary response function (TQ) and
the upwelling longwave flux (LWot) are summarized in Table 6.
As discussed earlier, the B_ and (3 _ terms describing the downwelling
longwave flux are derived from the harmonic analysis of the pyrgeometer
measurements at the surface station. These values have been taken as
representative of conditions at all nine surface test areas.
65
-------
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68
-------
Estimates of the amplitude and phase terms for the atmospheric
flux of sensible heat follow from Eqs. (13) through (15). The aero-
dynamic surface roughness is computed with Eq. (15a) using characteristic
physical heights estimated from the aerial photographs for the various
sites (see Figs. 13 through 21). The geostrophic wind was estimated
from the two NWS low-level EMSU soundings (0600 and 1130 CST) to be
about 6.5 m sec . After computing the surface Rossby number at each
site, the geostrophic drag coefficient and the surface friction velocity
are determined from Eq. (15). Terms $ and cp have been tabulated in
Table 6 based on Eq. (14) and the following constant values: a = b = 8.5;
c = 17, and M* = 0.2.
Having parameterized the radiative fluxes and the atmospheric
sensible heat flux, the solutions for both the evaporative and the
subsurface heat fluxes are obtained by using the known amplitude and
phase terms together with Eqs. (8) and (9). Since i|r and x are known,
both V and X, and subsequently (j, and Bo can be evaluated with Eqs. (12c)
and (16a), respectively. In the case of the partial impedance for
evaporation the sum of $ and X has been evaluated using Eqs. (8) and (9);
the X-values are then obtained as the residual using the $-values as
discussed above. The thermal admittance p, follows from fusing Eq.
(12c). The values for W, Bo, and (j, evaluated in this manner using
first harmonic amplitude and phase terms were summarized in Table 6.
In summary, we have taken measured radiative parameters and certain
parameterized (synthesized) values and through the application of
climatonomy have determined two important geophysical features of the
sites: the thermal admittance (|_i) is obtained through consideration
of the submedium at each site as a homogeneous conductor of heat; the
inverse Bowen ratio (Bo) expresses the magnitude of the evaporative heat
flux as a fraction of the sensible flux of heat to/from the atmosphere
at the earth/air interface. Keeping in mind the limitations noted both
69
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in the measured and parameterized values, it is possible to subjectively
evaluate the representativeness and significance of the results. It is
encouraging to note that all sites have p,- and Bo- values that are in
the range of what might be anticipated. For example, y, ranges from a
minimum of 22 mly sec"-*-/2 °K in open farm country (R-7) to a maximum
of about 87 at the wooded sites (R-8 and R-9); the mean value for all
sites is 42. Lettau9 lists typical p-values determined for a variety
of homogeneous media: soils range from 14 mly sec"1'2 °K for fine,
dry quartz sand to 47 for the same sand with 22% moisture; y, for "sandy
clay (15% moisture)" is given as 36 while "swamp land (90% moisture)" is
44. Rocks range from 45 for basalt to 56 for granite and concrete.
Regarding heterogeneous surfaces, Lettau estimates "fields, weedy swamp,
still water, and hilly woods" to have y,-values of 35. Examining our
results in view of this background, several conclusions may be drawn.
First, the absolute values of the computed thermal admittances are
reasonable. Second, the highest values occur at sites R-2, R-8, and
R-9. These three sites share one common feature not typical of any of
the other six sites: they are all dominated by a high percentage of
wooded areas. It is interesting, however, that Lettau estimates y, to be
smaller by a factor of 1.5 to 2 for similar terrain, although he does not
state whether his estimate is a summer or winter value. It is quite
conceivable that the presence or absence of foliage significantly alters
the effective thermal conductivity of a wooded area and that the former
situation may lead to larger values of y, as a result of the increased
surface area and concurrent increase in mixing and the transfer of heat
away from the canopy.
The "developed" sites (R-3, -4, -5, and -6) all have quite similar
values of the thermal admittance, around 25 mly sec~l/2 °K~ . There does
not seem to be any noticeable difference in y, among the various building-
zone types; i.e., new and old residential and commercial all appear
70
-------
similar. One possible exception is site R-6, where p, computed from the
lower level aircraft data seems somewhat low. No conjecture is offered
in explanation.
Site R-7 is a good check on the method as the site is simple,
homogeneous and extensive, and experience dictates a low value for u,
Lettau9 estimates 35. The two ^-values for this site are 32 and 13,
averaging out to 23.
Without supporting surface observations, it is difficult to evaluate
all of the Bo-values. Most values are less than 2.5, with site R-7 the
maximum, having an average Bo of 3.5. There had been showers in the
area on 8 August and hence the Bo-values are not unreasonably large. It
is significant that the lowest values are found for three of the four
developed sites, R-4, -5, and -6. This is to be expected due to the
increased runoff in urban and suburban areas and the corresponding
decrease in evaporation.
A final observation is in order regarding the distribution of u.
and Bo at the nine sites: although the theoretical formulation used in
evaluating the surface energy budget explicitly ignored energy fluxes
associated with photosynthesis (or anthropogenesis), the impact,
if any, of such fluxes is reflected in the measured values. Hence in
using the climatonic theory in the valuation of p, and Bo as (essentially)
residuals, we have implicitly accounted for the impact of such other
fluxes in the determination of these parameters. Thus, for example, it
is not unlikely that the large Bo-values determined for the undeveloped
sites relects some impact of photosynthesis. This may in part explain
why the largest Bo-values were found for the agricultural site.
The |j,- and Bo-values tabulated in Table 6 are the result of the
analysis of the first-harmonic data. Since ^ and Bo are frequency-
independent, all harmonics should yield similar results. Difficulties
71
-------
were encountered in attempting to evaluate both parameters on the basis
of the second-harmonic data: y,-values became negative, while Bo was
excessively large in many cases (up to 25). There are three possible
explanations for these discrepancies: (1) errors in the regression
analysis used to infer the amplitude and phase terms from the surface
temperature data, (2) experimental inaccuracies such as instrument
drift or (more likely) wander of the flight track, and (3) limitations
in the theoryparticularly in the neglect of photosynthetic and
anthropogenic fluxes. Most likely, each contributes to the problem. On
the assumption that the cause lay in the data and particularly in the
determination of the second-harmonic terms, a simple feedback analysis
was pursued wherein effective AT- and 6 -values were derived that
2t O £
forced the determination of u.- and Bo-values equal to the first-harmonic
results. In 16 of the 18 cases, the "effective" temperature amplitude
(A2T0) differed from the original (Table 6) by less than 0.7°C; phase
differences were generally larger, averaging about 0.6 rad or 70 min.
Differences in both terms are certainly within the range of possible
errors associated with the regression method for determining Fourier
coefficients (see Section V-B) and/or with departures from the aircraft
flight track (leading to differences in scene at the nine sites from
flight to flight).
Table 7 then summarizes the amplitudes of the atmospheric sensible
and latent heat flux densities and the subsurface heat flux density on
the basis of (1) the first-harmonic (j,- and Bo-values, as derived above,
and (2) the temperature amplitudes (A^TO) determined earlier from the
regression approach. To illustrate the diurnal fluctuations of these
fluxes and their variations among land-use types, Figure 25 illustrates
these differences for three sites: farmland (R-7), commercial/industrial
(R-4), and new suburban residential (R-3) . The curves have been derived
from Eqs. (2d through f) using averaged amplitude terms from Table 7 and
phase terms from Table 6.
72
-------
Table 7
DERIVED AMPLITUDE TERMS FOR ATMOSPHERIC SENSIBLE (AiQo),
LATENT (AiE0), AND SUBSURFACE (AiSo) HEAT FLUX DENSITIES
Units: mly/min
Site:
Altitude*
R1:U
R1:L
R2:U
R2:L
R3:U
R3:L
R4LU
R3:L
R5:U
R5:L
R6:U
R6:L
R7:U
R7:L
R8:U
R8:L
R9:U
R9:L
A Q
1 0
103
112
106
122
124
131
155
211
183
212
179
204
87
107
91
101
105
111
A2Qo
36
34
38
57
49
55
79
96
70
85
76
99
37
36
24
28
33
25
A E
1 0
217
194
125
251
364
298
229
165
178
170
250
235
319
352
33
254
264
174
A E
2 o
76
59
45
117
143
125
116
75
68
68
106
114
135
120
9
70
82
40
AS
1 0
229
235
325
166
55
109
174
156
194
159
119
101
144
73
435
199
190
275
2 o
107
94
157
103
28
60
116
93
98
84
66
64
81
33
154
72
80
83
*
U = upper (1220 m mgl)
L = lower (460 m mgl)
73
-------
400
10 15
LOCAL TIME hours
20 25
SA-2322-39
FIGURE 25 DIURNAL. VARIATION OF DERIVED DEPARTURES
(FROM DAILY AVERAGE) OF ATMOSPHERIC,
LATENT, AND SUBSURFACE HEAT FLUX DENSITIES
FOR THREE LAND-USE TYPES: FARMLAND ( ),
COMMERCIAL/INDUSTRIAL ( ), AND SUBURBAN
RESIDENTIAL ( )
74
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VI CONCLUSIONS AND RECOMMENDATIONS
All of the data collected during the experimental programs in St.
Louis have not been fully exploited for information content. Additional
analyses would include not only the aircraft observations but also a
variety of surface observations collected during the same period under
other observation programs. Detailed photographic analysis was limited
by the scope of the present study. Nevertheless, the program demon-
strated the feasibility of acquiring observations of the time changes
in the solar forcing function and the primary response function (surface
temperature) and for inferring, in conjunction with climatonomic theory,
secondary responses as a function of surface type. In this way variations
in the surface energy budget are described. Magnitudes and variations
in both observed and derived quantities were established by the program,
and a useful evaluation of program requirements for future applications
is now possible.
Considerable rechecking of both observational and theoretical results
with independent data is of course, desirable. Improvements in data
acquisition and processing techniques would be introduced as a result of
past experience. Although it is easy to expand an observational program,
certain improvements must be given priority. From the aircraft platform,
measurements of reflected solar radiation and surface infrared emission
should be obtained with the same field of view, and over a complete 24-
hour period (with overlap). Furthermore, solar radiation measurements
(in both directions) should be expanded so as to permit a separation of
visible and near-infrared contributions.
The program for the analysis of other standard aircraft data could
be expanded considerably with a good payoff to a study of the type
75
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conducted. Because of the importance of small changes in the surface
albedo and surface temperature, more effort is required to assess the
magnitude of the atmospheric influence on these measurements (by virtue
of observed changes with altitude). A more careful analysis of the air
temperature data collected at each of the two flight altitudes provides
information on changes in stability and advection within the boundary
layer; corrections for cooling or heating during each traverse can be
accomplished with the observations themselves. In addition, harmonic
analyses of the aircraft-measured temperature in the boundary layer over
each site of interest would assist in the analyses of the secondary
response terms in the climatonomical analysis of the surface energy
budget. Finally, inasmuch as ground-speed determinations between check
points are documented, wind estimates at two altitudes along the flight
track could be obtained fron the indicated air speed, ambient temperatue,
and drift angle. Because of the need for a more careful representation
of flow conditions, this wind information should be supplemented with
additional surface wind observations at locations along the track and
with at least four balloon soundings per day at one location. Together
these data would provide a more detailed assessment of the temporal and
spatial variations in the atmospheric flux of sensible heat.
Surface radiation observations (along with temperature, humidity,
and wind) should be expanded to cover several preselected sites of
different types along the flight track. Better descriptions of surface
structure with improved input information on roughness and potential
evapotranspiration are required. Inventories also are required on
photosynthetic and anthropogenic heat sources, both of which have been
neglected thus far.
Lastly, several important improvements need to be made in the
aircraft operations. First, more frequent flights over a 24-hour period
need to be made: on the order of 10 to 12. This is necessary to over-
76
-------
come potential difficulties in the determination of Fourier coefficients.
Secondly, more active control of the aircraft flight path needs to be
implemented to assure repeated overflights of the identical surface scene.
The results to date are encouraging: the study has demonstrated the
feasibility of this method for evaluating the structure of the surface
energy budget. Incorporating experiences and the recommendations herein,
we recommend the program be expanded to evaluate in a systematic fashion
the geophysical surface features of a broad range of typical land-use types
under varying meteorological conditions. In this way we will be able to
look at such interactions as the impact of soil moisture on thermal
admittance, foilage and its effect on albedo, and so forth.
77
-------
Appendix A
AIRCRAFT DATA SUMMARY
-------
Appendix A
AIRCRAFT DATA SUMMARY
Most of the aircraft measurements of solar radiation, surface
temperature, and air temperature are summarized graphically in this
appendix (Figures A-l through A-14).* All data are plotted as a function
of flight track range. The origin of the range for August 1972 data
coincides with the northernmost checkpoint of the August 1972 flight
track shown in Figure 2 of the text; the range for April 1973 data
originates at the westernmost checkpoint shown in Figure 2. These origins
are maintained regardless of the direction of motion of the aircraft at
either of the two flight altitudes. The major urban area for August
flights falls between about 33 and 45 km range while the major rural
areas occur over the last two-fifths of the track. Along the April flight
track the urban area is more varied; the major portion of the urban areas
occur between about 26 and 47 km range while the major rural areas occur
over the last third of each flight track.
Solar data are presented for the August flights only. The characteristic
dip in the albedo traces near the origin results from crossing a broad
section of the Mississippi River (see Figure A-l); a broad dip in the
albedo curves occurs over the urban area. Irregularities in the measured
downwelling solar irradiance (solid curve) are produced by clouds above the
aircraft and are frequently associated with irregularities in the albedo
curves as well, especially when the aircraft pyranometer is shaded but the
surface directly beneath the aircraft is not shaded. Variations in incident
solar radiation with changes in solar zenith angle also are revealed by
time changes in the solid curves. Especially characteristic of convective
activity are the data for the 1630 CDT flight on 11 August 1972 (Figure A-9);
*For convenience, the illustrations for this appendix are grouped after
this discussion.
A-3
-------
showers forced cessation of the observational sequence at this time.
The sequence of radiometric surface temperatures for 9 August 1972
(Figure A-10) clearly shows the pronounced increase in surface temperature
variability associated with daytime solar heating. At night the surface
temperatures are relatively uniform except for water bodies (rivers),
which appear as pronounced warm spikes. These spikes provide an
excellent nighttime check on the actual flight track. The low-level
flights of 0400 and 0630 CDT actually strayed too far to the east as
evidenced by the double spikes appearing between 25 and 31 km range;
these correspond to two crossings of a bend in a Mississippi River
channel along the northeastern border of St. Louis (cf., Figure 2). As
the land areas heat to their maximum temperatures, the water bodies
appear as minima on the temperature curves.
Figure A-ll portrays graphically the air temperature as a function
of range at both altitudes; a comparison of the traces provides an
immediate indication of stability (above 460 m) . These records are
sensitive to slight changes in aircraft altitude; unfortunately, a precise
altitude record was not available for the data. If it is assumed that the
data have been properly calibrated and that the aircraft altitude was
essentially uniform along each leg, then it appears that at the start of
the period cold air advection (with northerly flow) was still occurring,
with greater stability between 460 m and 1220 m over the rural area along
the southern portion of the track (beyond 50 km range). By afternoon the
temperatures have become more uniform and the stability has decreased.
Data in Figure A-12 for 11 August 1972 are similar to those in
Figure A-10 for 9 August 1972. In Figure A-13 (11 August 1972), the
air temperature data conte.in many noise spikes; these spikes should be
ignored. Nighttime data for 11 August suggest less stability beyond
50 km range in contrast to the observations of 9 August. Of course, from
A-4
-------
the surface temperature measurements it is also clear that the same
region has much greater stability below the 460 m altitude. Nevertheless,
the trend of the airborne air temperature data is disturbing, showing
an increase with flight time (460 m flown first on this flight sequence).
Therefore, a firm picture of the air temperature fields in the early morning
periods cannot be established without more observations supplying accurate
calibrations and a careful check on flight altitudes.
The surface temperature measurements from the April 1973 flights
(Figure A-14) shows the extensive flooded area around the Mississippi
River near the origin of the flight track. This region is relatively
cool during the 1700 CST flight but, as the land cools, appears relatively
warm in the early morning hours. The large dip in the dashed trace at
0130 CST should be ignored (10°C not added).
A-5
-------
£ 2.0
'£
1.0
01
IT
0.5
DOWN
UP
ALBEDO
20 40 60
RANGE km
(a) FLIGHT ALTITUDE 1220 METERS
80
17.5
15.0
12.5
100
I 2'°
u
g 1.5
LLI
0
IT
DC
1.0
0.5
I /
I I
ALBEDO -
DOWN
UP
I
20 40 60
RANGE km
(b) FLIGHT ALTITUDE 460 METERS
80
17.5
15.0
12.5
100
SA-2322-24
FIGURE A-1 AIRCRAFT SOLAR MEASUREMENTS, 0930 CDT FLIGHT,
9 AUGUST 1972
A-6
-------
1.5
LU
O 1.0
CC
E 0.5
DOWN
UP
ALBEDO
20 40 60
RANGE km
(a) FLIGHT ALTITUDE 1220 METERS
80
17.5
15.0
12.5
100
2.0
3 1.5
S
J
) 1 .0
>
c
5
c
: 0.5
0
I ' I ' I ' I
_
% ~» »'*»'"x*x
,-v /' *"*\ «% ,''' *
', /' '' '\ ,' '.'' ALBEDO ~-
\ '
^ .\.'
* '
DOWN
~ A /^ "
'. -
UP
I , I . I . I
17.5
15.0
12.5
20 40 60
RANGE km
(b) FLIGHT ALTITUDE 460 METERS
80
100
SA-2322-25
FIGURE A-2 AIRCRAFT SOLAR MEASUREMENTS, 1145 CDT FLIGHT,
9 AUGUST 1972
A-7
-------
c 2.0
E
1 1-0
DC
o:
0.5
ALBEDO-
DOWN
UP
I
I
20
40
60
km
RANGE
FLIGHT ALTITUDE 1220 METERS
80
17.5
15.0
12.5
100
'c 2.0
E
CN
\
CJ
IS 1-5
10
(E
DC
0.5
ALBEDO
UP
I
20
40
60
80
RANGE km
(b) FLIGHT ALTITUDE 460 METERS
17.5
15.0
12.5
100
SA-2322-26
FIGURE A-3 AIRCRAFT SOLAR MEASUREMENTS, 1400 CDT FLIGHT,
9 AUGUST 1972
A-8
-------
E 2.0
E
1
tr
oc
0.5
ALBEDO
DOWN
UP
20 40 60
RANGE km
(a) FLIGHT ALTITUDE 1220 METERS
80
17.5
150
12.5
100
I 2.0
LU
o
cc
DC
1.0
0.5
DOWN
UP
ALBEDO
20 40 60
RANGE km
(b) FLIGHT ALTITUDE 460 METERS
80
17.5
15.0
12.5
100
SA-2322-27
FIGURE A-4 AIRCRAFT SOLAR MEASUREMENTS, 1630 CDT FLIGHT,
9 AUGUST 1972
A-9
-------
'c 2.0
E
CM
'E
u
"5 1.5
u
LU
0
2 1.0
5
EC
cc
0.5
0
I I I I
-
' .,----» >
» ," »
\ »
» ' ». » %» . /
_ *»' *«''». ALBEDO _
,
'
DOWN
^^\ __ ^ ^^ ^^ -
- -
UP
. ( . T_,.__ j ^ ^ _
17.5
15.0
12.5
20 40 60
RANGE km
FLIGHT ALTITUDE 1220 METERS
80
100
SA-2322-28
FIGURE A-5 AIRCRAFT SOLAR MEASUREMENTS, 1915 CDT FLIGHT,
9 AUGUST 1972
A-10
-------
c 2.0
E
1.5
m
o
-------
2.0
SI C
I ,
-------
I 2.0
j
5 1.5
J
J
I i-o
5
.
c
-
0.5
n
1 ' 1 ' 1 ' 1
_ -
- .
\ , ' "-», /> / » ' \ ,'
- 1 ,*»-- « , --x .'
' . » /-. /
» . » . * t AI nrnn mi
* \ 1
* 1 V I
\ -».''
\'
~
DOWN
i
-
UP
1 . 1 . 1 . 1 .
17.5
15.0
12.5
20 40 60
RANGE km
la) FLIGHT ALTITUDE 460 METERS
80
100
.£ 2.0
5 1-5
LU
O
1.0
IT
IT
0.5
'DOWN
UP
ALBEDO
20 40 60
RANGE km
(b) FLIGHT ALTITUDE 1220 METERS
80
17.5
15.0
12.5
100
SA-2322-31
FIGURE A-8 AIRCRAFT SOLAR MEASUREMENTS, 1400 CDT FLIGHT,
11 AUGUST 1973
A-13
-------
'c 2.0
E
CM
I
U
UJ
CJ
5 1.0
DC
DC
0.5
II
I >
I >
UP
i :'"~"\"
I
20
40
60
km
ALBEDO
RANGE
(a) FLIGHT ALTITUDE 460 METERS
80
17.5
15.0
12.5
100
5 2.0
1.5
UJ
o
< 1.0
DC
DC
0.5
\ ALBEDO
* .» '«
V I ,/ ,
' > " ,« 'i
> ' '« 11
» ' t i t
UP
r
i
20 40 60
RANGE km
(b) FLIGHT ALTITUDE 1220 METERS
80
17.5
15.0
12.5
100
SA-2322-32
FIGURE A-9 AIRCRAFT SOLAR MEASUREMENTS, 1630 CDT FLIGHT,
11 AUGUST 1973
A-14
-------
50
40
30
20
10
30
I 20
uj
DC
D
DC 10
UJ
a.
5
UJ
in 30
OC
a.
20
10
I 'I
(d) 1145 CDT
'
30 -
20 -
10 -
(c) 0930 CDT
(b) 0630 CDT
(al 0400 CDT
10
20
40 60
RANGE km
80 100
SA-2322-33A
FIGURE A-10 AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE
MEASUREMENTS, 9 AUGUST 1972
Solid curve: measurements from 460 m
Dashed curve: measurements from 1220 m, 10°C added.
A-15
-------
50
40
30
20
40
UJ
cr
30
DC
UJ
Q.
uj 20
H
10
(e) 1400 CDT
111
/ l"l
I t
,;;. , i''j i.
»i ! r> < ", '<
>' ', i;;1.,'ijl;'.- jJli./!.
. i"! .nlfi m
(f) 1630 CDT
30 h
20
10
rVvV^^
(g) 1915 CDT
" JklV^vHr i/J^^^
20
40
RANGE
60
km
80 100
SA-2322-33B
FIGURE A-10 AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE
MEASUREMENTS, 9 AUGUST 1972 (Concluded)
Solid curve: measurements from 460 m
Dashed curve: measurements from 1220 m, 10°C added
A-16
-------
o
25
20
15
10
5
20
15
10
5
IT
cu
1 20
HI
I-
m
_J
DC
Q
15
10
5 -
20 h
15
10 -
5 -
(d) 1145 CDT
(c) 0930 COT
(b) 0630 CDT
(a) 0400 CDT
I
20
40 60
RANGE km
80 100
SA-2322-34A
FIGURE A-11 AIRCRAFT AIR TEMPERATURE MEASUREMENTS,
9 AUGUST 1972
Altitudes: 460 m (solid) and 1220 m (dashed)
A-17
-------
25
20
15
10
25
20
LU
CC
15
10
D
CD
25
CC
Q
20
15
10
20
(e) 1400 CDT
(f) 1630 CDT
(g) 1915 CDT
J
40 60
RANGE km
80 100
SA-2322-34B
FIGURE A-11 AIRCRAFT AIR TEMPERATURE MEASUREMENTS,
9 AUGUST 1972 (Concluded)
AltitJdes: 460 m (solid) and 1220 m (dashed)
A-18
-------
60
50
40
30
20
10
30
20
LU
CE
D
E
HI
Q.
in 10
h-
QC
Q.
30
20
io
30 -
20 -
10
\ ' I
I r
20
(d) 0900 CDT
(c) 0630 CDT
(b) 0330 CDT
(a) 0030 CDT
40
RANGE
60
km
80 100
SA-2322-35A
FIGURE A-12 AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE
MEASUREMENTS, 11 AUGUST 1972
Dashed curve: measurements from 460 m, 10°C added
Solid curve: measurements from 1220 m
A-19
-------
60
50
40
30
20
p 50
40
DC
LLJ
30
DC 20
Q-
50
40
30
20
10
.»$; ?
r *w
I I r
(e) 1130 CDT
(f) 1400 CDT
(g) 1630 CDT
I
20
40
RANGE
60
km
80 100
SA-2322-35B
FIGURE A-12 AIRCRAFT RADIOMETRIC SURFACE TEMPERATURE
MEASUREMENTS, 11 AUGUST 1972 (Concluded)
Dashed curve: measurements from 460 m, 10°C added
Solid curve: measurements from 1220 m
A-20
-------
30
25
20
15
25
20
15
OC
25
LU
I-
20
DC
Q 15
25
20
15
10
-,-'."*"'
20
1 ' I
Id) 0900 CDT
(c) 0630 COT
(b) 0330 CDT
(a) 0030 CDT
I
40 60
RANGE km
80 100
SA-2322-35A
FIGURE A-13 AIRCRAFT AIR TEMPERATURE MEASUREMENTS,
11 AUGUST 1972
Altitudes: 460 m (dashed) and 1220 m (solid)
A-21
-------
30
25
20
35
o
30
oc
525
X
HI
Q.
HI
K 20
co
cc
Q
35
30
25
20
15
j*^-*-^r^vvv>*v^r^^^^^
(el 1130 CDT
(f) 1400 CDT
(g) 1630 CDT
.'V.'.-
I
20
40 60
RANGE km
80 100
SA-2322-35B
FIGURE A-13 AIRCRAFT AIR TEMPERATURE MEASUREMENTS,
11 AUGUST 1972 (Concluded)
Altitudes: 460 m (dashed) and 1220 m (solid)
A-22
-------
40
30
20
10
30
20
10
30
I-
ir 20
10
H
tt
30
20
10 -
10 -
(a) 1700 CST
(bl 1930 CST
(c) 2230 CST
(d) 0130 CST
(e) 0430 CST
20
40 60
RANGE km
80 100
SA-2322-36
FIGURE A-14 AIRCRAFT RADIOMETRIC SURFACE
TEMPERATURE MEASUREMENTS,
23-24 APRIL 1973
Dashed curve: measurements from 460 m, 10°C added
Solid curve' measurements from 1220 m
A-23
-------
REFERENCES
1. H. E. and K. Lettau, "Exploring the World's Driest Climate: Scientific
Results of the University of Wisconsin Field Studies during July 1964,
in the Peruvian Dessert (Pampa de la Joya), pre-publication draft,
Madison, Wisconsin (1971).
2. E. E. Uthe, "Lidar-Derived Aerosol Structure over St. Louis, Missouri,
during METROMEX 1972',' Interim Report, NSF Grant GI-34770, Stanford
Research Institute, Menlo Park, California (1972).
3. Physics of Plant Environment, W. R. VanWijk, Ed., (North-Holland
Publishing Company, Amsterdam, 382 pp, 1963).
4. W. C0 Swinbank, "Long-Wave Radiation from Clear Skies" Quarterly
Journal of the Royal Meteorological Society, 381, 339-348 (1963).
5. W. F. Dabberdt, "Climatonomy of the Antarctic Plateau," paper presented
at the Conference on Planetary Boundary Layers, 18-21 March 1970,
sponsored by IUGG, IAMAP, and AMS, Boulder, Colorado.
6. E. Kung, "Climatology of Aerodynamic Roughness Parameter and Energy
Dissipation in the Planetary Boundary Layer over the Northern Hemisphere,
Section 2 of Studies of the Effects of Variations in Boundary Conditions
on the Atmospheric Boundary Layer, Department of Meteorology, University
of Wisconsin, Annual Report Contract DA-36-039-AMC-00878, USAERDA, Ft.
Huachuca, Arizona (1963).
7. H. Panofsky, and G. N. Brier, Some Applications of Statistics to
Meteorology, (Mineral Industries Continuing Education, Pennsylvania
State University, University Park, Pa. 224 pp, 1965).
8. S. Changnon, "1972 Operational Report for METROMEX',' Illinois State
Water Survey, Urbana, Illinois (1972).
9. H. H. Lettau, Micrometeorology Syllabus, Meteorology 403, Department
of Meteorology, University of Wisconsin, Madison, Wisconsin (1968).
R-l
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