United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
II \
Research and Development
EPA/600/S3-86/040 Nov. 1986
Project Summary
Project CONDORS—
Convective Diffusion
Observed by Remote Sensors
J. C. Kaimal, W. L Eberhard, W. M. Moninger, J. E. Gaynor, S. W. Troxel,
T. Uttal, G. A. Briggs, and G. E. Start
This data report presents results from
two diffusion experiments conducted
at the Boulder Atmospheric Observa-
tory (BAO) of the National Oceanic and
Atmospheric Administration (NOAA) in
1982 and 1983. The objective was to
compare diffusion in the atmospheric
convective boundary layer with that
observed in laboratory tank experiments
and numerical computer models. In
both experiments at the BAO, two
different tracers, oil fog and aluminized
chaff, were released simultaneously and
tracked by lidar and radar, respectively,
for periods up to two hours. In 1982,
both tracers were released from the
same surface or elevated point; in
1983, the two were also released from
separate levels, the oil fog from near the
surface, the chaff from an elevated
point on the tower. The 1983 experi-
ment included tracer gas releases with
in situ samplers measuring surface
concentrations downwind of the tower.
The BAO tower provided data on the
mean and turbulent state of the atmos-
phere, while mixing depths were moni-
tored by balloon soundings, sodar, lidar,
and radar. A detailed description of the
experiment and the measurements ob-
tained from the different sensors is
provided. The strengths and limitations
of the experiment are discussed in the
context of case studies.
This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering in-
formation at back).
Introduction
Project CONDORS (Convective Diffu-
sion Observed by Remote Sensors) was
undertaken to provide field data on dif-
fusion in three dimensions at short
ranges, 0.1 to 3.5 km, in convective
conditions. These conditions prevail over
land during sunny to partly cloudy days
with light to moderate wind speeds,
especially when surface heating is mod-
erate to strong. This volume is a data
report on Project CONDORS, later to be
followed by scientific analyses of the data
published in peer-reviewed journals.
The need for such an experiment
became evident after unexpected results
for vertical diffusion were obtained from
laboratory experiments in a convective
water tank by Willis and Deardorff (1976a,
1976b, 1978, 1981) and from computer
modeling experiments by Lamb (1978,
1979). The concentration (X) patterns in
downwind distance (x) and in height (z)
were substantially different from those
resulting from conventional Gaussian
diffusion models. For releases near z=0.5
Zi, where z\ is the mixing depth, maximum
surface X was found to be about twice
that predicted by Gaussian models. (Mix-
ing depth refers to a layer of vigorous
mixing due to convective turbulence
produced by surface heating; this layer is
always capped by a layer of stable air,
which often is marked by a temperature
inversion just above zi.) For elevated
releases, the centerline of maximum
averaged X was observed to descend with
distance from the source height, nearly to
the surface; thereafter, the plume be-
haved much like a surface release. For
surface releases, the maximum averaged
X remained near the surface up to a time
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typifying the flow of air from downdrafts
to updrafts (thermals); then it rapidly
lifted into the upper half of the mixing
layer.
The above-mentioned laboratory and
computer modeling experiments, as well
as turbulence measurements in the mix-
ing layer at a variety of sites, also showed
the importance of the length scale z, and
the velocity scale w* to turbulence and
diffusion in convective boundary layers
(CBLs) (w* = (H*Zi)1/3, where H* is the
vertical flux of buoyant accelerations
produced by sensible heating and water
vapor flux near the surface; for surfaces
not very moist, H* = (g/T)w'T; where g is
gravitational acceleration, T is absolute
temperature, and w'T' is the vertical
turbulent flux of temperature variations).
Average diffusion patterns in CBLs scale
best with z, and the time scale z,/w*. The
time after release, t, can be estimated as
x/u (the mean wind speed, u, is almost
constant with z through most CBLs,
because of vigorous vertical mixing).
Diffusion results from various experi-
ments in CBLs tend to agree well when
expressed in terms of dimensionless time
or distance, X = (x/u)w*/z, = tw*/z,.
Unfortunately, very few past diffusion
experiments in the field included suffi-
cient meteorological measurements to
determine w* or z*; furthermore, they are
limited to measurements of X at the
surface or on towers no higher than 62 m.
Measurements of X are needed up to z —
zi, which is usually of the order of 1000m.
To verify the new laboratory results for
convective diffusion, particularly the non-
Gaussian vertical behaviors, data from a
field study were needed. The CONDORS
field experiment was designed to go
beyond the limitations of past diffusion
experiments in two ways. First, a large
number of high-quality meteorological
measurements were made so that essen-
tial quantities like w*, z,, and u could be
determined with accuracy and redun-
dancy. Many less essential measure-
ments werealso collected; e.g., unusually
detailed information on wind direction
statistics. Second, remote sensors were
used to define mean X fields in three
dimensions through depths up to 2000m,
easily encompassing zi. Two independent
tracer-sensor systems were used, lidar to
detect oil fog and Doppler radar for
detection of metalicized "chaff." Also,
limited conventional gaseous tracer
measurements were made at the surface;
these served primarily to test the infer-
ences made about conservative-sourceX
on the basis of observed distributions of
oil fog and chaff, which are not conserva-
tive (oil fog droplets tend to vaporize and
chaff tends to settle out).
Operational Plan
The CONDORS experiment was carried
out in 1982 and 1983 at NOAA's Boulder
Atmospheric Observatory (BAO), operated
by the Wave Propagation Laboratory
(WPL), under an interagency agreement
between EPA and WPL. In 1983, an
additional interagency agreement be-
tween EPA and NOAA's Air Resources
Laboratory Field Office (ARLFO) provided
for sampling and analysis of gaseous
tracer releases. WPL provided the site,
most of the personnel, meteorological
measurements, radar and lidar meas-
urements, and followup data processing.
The 1982 experiments consisted of
four runs of two hour's duration carried
out on separate days in September. The
four runs were intended primarily as trial
runs to test the adequacy and the limita-
tions of the two remote sensor tech-
niques. The oil fog generator and chaff
dispenser were located within a few
meters of each other to permit direct
comparisons of the observed X distribu-
tions. The runs were split evenly between
elevated releases and surface releases.
These experiments were successful
enough to provide six averaging periods
with usable chaff and/or oil fog distribu-
tions plus adequate meteorological data.
The 1983 experiments included surface
sampling of tracer gases and consisted of
eight runs of two hour's duration on
separate days in late August to mid-
September. Based on conclusions follow-
ing some analyses of the 1982 runs, it
was decided to use the chaff only in the
elevated release mode in 1983. Two more
runs with collocated elevated releases
were made; during the remaining six
runs, the oil fog was released from the
surface so that independent measure-
ments of simultaneous elevated and
surface releases could be made. These
eight runs provided 11 averaging periods
with relatively steady meteorological
variables and good chaff and/or oil fog
measurements.
Preparation for a typical run began with
a check of daily National Weather Service
forecast maps. A forecast including clear
to partly cloudy skies, Colorado under the
influence of a surface high, and light to
moderate geostropic winds was consid-
ered favorable for a run; all field personnel
were notified of the weather outlook.
Near sunrise on promising days, a raw-
insonde was released at the BAO and
tracked by double theodolite to about
3000 m AGL The data were quickly
processed into temperature, humidity,
wind speed and direction profiles and
transmitted to the main WPL laboratory in
Boulder. This sounding, supplemented by
the 1200Z sounding at Stapleton Airport
in Denver, was the main basis for deciding
whether to send personnel to their sta-
tions in the field, about 25 km east of
Boulder. In 1983, the sounding data were
input into a numerical model for z, de-
velopment; this facilitated the decision
making, especially the choice of optimum
times to initiate runs (slow z, growth
during runs was desired).
At the CONDORS site, z, development
was monitored using tower profiles and
turbulence measurements up to 300 m,
acoustic sounder records up to about 600
m, lidar reports of haze heights, and radar
reports of heights of natural reflectors
(thought to be insects). When z, developed
into the desired range and the winds on
the tower entered into the desired speed
range (2 to 6 m/s) and direction sector
(NE to SE), a run initiation time (RIT) was
called. The elevated source height was
chosen on the basis of predicted z, for the
middle of the run, attempting to set this
height at about 1 /4 or 1 /2 z, to duplicate
the laboratory and computer modeling
runs. About 15 minutes were required for
the release height to be reached by the
carriage on the 300-m tower. Tracer
releases were begun 10 to 20 minutes
prior to RITto allow plume transport out to
the distances of greatest interest (about
ZiJ/w*). The lidar crew was advised of
preferred lidar azimuths, which also
depended on the expected value of the
length scale z,u/w*. Sampler, lidar, and
radar acquisition began at RIT and con-
tinued for two hours, or slightly longer if
wind velocity remained in the acceptable
range (during both years at least one run
was aborted due to sudden wind direction
change).
Siting
The BAO site was chosen primarily for
the excellent meteorological measure-
ments available on the 300-m tower and
the convenience of a release platform
that can quickly be elevated up to 300 m
(the carriage attached to the west side of
the tower). Another convenient factor
was the close proximity of WPL's person-
nel and facilities, including the Doppler
radar, the lidar, acoustic sounders, data
loggers, and computers. The site has both
advantages and disadvantages for this
type of experiment. The terrain is gently
rolling, neither "ideal" nor complex, and
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is somewhat typical of developed land
surface. Convective conditions predom-
inate during spring, summer, and fall
days; late summer was chosen for the
experiment because z, is likely to be in the
desired range, and cloudy or rainy spells
are less likely than in the fall. During
convective conditions, the midday wind
direction is almost always from the NE, E,
or SE. This is thought to be caused by
upslope flow on the heated eastern slopes
of the Front Range of the Rocky Moun-
tains, 25 to 50 km west of the BAG. The
prevalence of winds from one direction
sector made it easier to effectively site the
lidar, the radar, and samplers during
CONDORS. On the other hand, the easter-
ly flow in the mixing layer was almost
always opposed to the upper winds; as z\
grows and entrains upper air, momentum
from above mixes downward; the opposi-
tion of upper and mixing layer wind
directions at this site probably causes
more variability in wind speed and direc-
tion than is common in CBLs farther from
large mountain ranges.
Siting of the sensors and samplers was
also guided by results of the laboratory
convective tank experiments and com-
puter simulations. The distance range of
most-needed X measurements was as-
sociated with travel times of about 0.3 to
1.2 z,/w*. As uzj/w* was typically 1 to 2.5
km during CONDORS runs, the most
desired distances of plume measure-
ments ranged from 0.3 to 3 km downwind
of the source. The radar is capable of
detecting chaff at much greater distances
than this, and the reflected signal is not
attenuated by travel back through the
plume. Consequently, the radar was sited
upwind of the BAO tower, 3.5 km to the
east, to reduce the azimuth and elevation
angles needed to encompass the plume
and to reduce the dynamic range of
returns due to 1/r2 attenuation. While
the radar scans horizontally, the lidar
scans in vertical planes, and the signal is
attenuated appreciably by travel through
the plume. Therefore, it was necessary to
site the lidar as close to perpendicular to
the plume axis as possible, at a distance
minimalizing the elevation angle range
needed but without too much signal
attenuation. The lidar was sited 3 km
from the BAO tower at 325° azimuth in
1982 and was moved to 4 km away at
346° azimuth in 1983, in anticipation of
more frequent southeasterly winds
(which proved to be the case).
Only one sampling arc could be oper-
ated within the available budget. The
sampling arc consisted of 29 samplers
placed every 5° of azimuth from 202.5° to
342.5°, mostly along roads. This arrange-
ment provided adequate angular resolu-
tion for the time-averaged plumes, which
were 30° to 90° wide at the arc distance.
The midpoint of the arc was 1.2 km to the
west of the tower, a good distance for
intercepting nearly maximum surface X
from the elevated release in almost every
case.
Tracers and Sensors
The primary mapping of plume concen-
tration fields was done by the two remote
sensors, radar mapping chaff and lidar
mapping oil fog. These techniques were
supplemented by conventional sampling
and gas chromatography analysis of
plumes containing conservative tracer
gases. Each of these three techniques
has some areas of advantage as well as
some substantial limitations.
Lidar is a well-proven tool for mapping
atmospheric aerosol fields and light-
reflecting plumes. The WPL lidar uses a
frequency-doubled Nd:YAG laser trans-
mitter firing at 10 pulses/s. It is easily
able to map atmospheric haze cross
sections several km deep; this capability
was valuable for making quick estimates
of z, during CONDORS runs. Oil fog was
used as a tracer because of the economics
of producing enough plume particles to
make the plume distinguishable from
atmospheric haze after dilution with
roughly 107 m3/s of air. In the com-
mercially built oil fogger used in CON-
DORS, oil is sprayed into a heated jet of
air, causing it to vaporize. On mixing with
ambient air, it cools and condenses into
drops a few microns in diameter which
are very efficient reflectors of laser light.
In 1982, a pale paraffin type oil was used,
which was not expected to significantly
evaporate as it travelled downwind; how-
ever, the decline of integrated return
signal from larger x scans suggested
otherwise. The maximum x of plume
distinguishable from ambient haze was
only 1.9 km, short of the experimental
goal. To improve this range to 2.9 km, in
1983 a heavier oil was used; this change
required modification of the fogger to
preheat the oil to reduce its viscosity. In
addition, a second oil fogger was operated
during surface releases; however, it could
not be accommodated on the tower
carriage for elevated releases.
The energy of each pulse and the
digitized photomultiplier detector signal
were recorded for later processing. Just
prior to each run, about six azimuths were
chosen for lidar scanning, which was
controlled by computer. Each scan at an
azimuth contained about 100 pulses,
beginning at a maximum elevation angle
that fully encompassed the plume. The
scans had to be terminated a few tens of
meters above the surface because the
laser beam was not eye-safe. The scan at
each azimuth was repeated approximately
every 210 seconds throughout the runs,
so that ensemble-averaged plume Xcould
be obtained. The spatial resolution of the
lidar was of the order of a few meters,
which was more than adequate.
Post-experiment lildar signal process-
ing for CONDORS achieved new levels of
quantification of plume returns in terms
of concentration fields. This required
considerable computer processing time
and man-machine interaction, as each
averaged scan had to be corrected for
attenuation of the signal by travel through
both background haze and the plume
itself. Because the oil fog droplet size
distribution was unknown, only the rela-
tive concentration field at each azimuth of
scan could be determined. Consequently,
to estimate X/Qfor a conservative tracer,
where Q is the release rate, Q was
replaced by the measured downwind flux
of relative X(u times JXdydz, where y is
the lateral dimension). This expedient
assumes that the droplet size distribution
and the percentage evaporation is con-
stant across each scan section.
In recent years, radar has been used to
map clear airflow structures using a
tracer called "chaff," aluminum-coated
mylar threads. During CONDORS, bun-
dles of these threads were unwound from
reels, chopped into 1.6-cm lengths, and
ejected by an air jet at the rate of 38,000
filaments/s by a "chaff cutter." The
majority of the filaments clump together
and quickly fall to the ground, but enough
single filaments are produced to provide
very reflective targets for WPL's 3.2-cm
wavelength Doppler radar. At typical
CONDORS ranges, the radar could easily
detect one filament in a (50 m)3 volume of
air. Acquisition of signal was limited to
x — 3.5 km because of the experimental
focus and high data processing costs. The
chaff volume was too small to be seen by
the lidar, and oil fog droplets are extremely
poor reflectors of X-band electromagnetic
waves, so the two remote sensor/tracer
systems were quite independent.
Chaff used as a tracer has one signifi-
cant drawback, namely, a settling speed
of about 0.3 m/s. Convective turbulence
has vigorous upcurrents of 1 m/s and
more, so chaff is easily mixed up through
the whole mixing layer, but it does not
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distribute exactly as a passive, non-
buoyant tracer (oil fog droplets are small
enough to have negligible settling speed).
This is the main reason that collocated
releases of chaff and oil fog were made, to
gauge this behavior. It was decided to use
chaff only for elevated releases in 1983
because it is relatively easy to correct the
distribution for settling speed effect be-
fore surface contact occurs; comparisons
of plumes from collocated oil fog and
chaff releases showed the expected
magnitudes of downward displacement
of chaff z (mean height). More sophisti-
cated correcton schemes can be applied
near the point of maximum surface
impact, but this is not done in the
CONDORS data report. At farther dis-
tances downwind, chaff deposition and
resuspension become additional compli-
cating factors which may frustrate at-
tempts to correct for settling effects.
The X-band Doppler radar used in
CONDORS has a beam width of 0.8° and
a pulse volume 90 m deep. Typically, the
radar swept horizontally through 1.2° of
azimuth during the dwell time (the time of
accumulation of sufficient return signal).
These factors plus distance determined
the typical spatial resolutions for radar
scans: 90 m downwind; 70 m vertical;
and 160 m crosswind. The radar swept
through enough azimuth to encompass
the plume to at lease x = 4 km and was
raised vertically by about 0.7° increments
to encompass the depth of the plume,
repeating the whole sequence about
every 135 seconds. The data for selected
averaging periods were later processed
and interpolated into Cartesian coordi-
nates with (50 m)3 cells. Most ground
clutter (strong reflections due to surface
objects) was avoided by purposely siting
the radar so that nearby terrain blocked
the beam below about 0.5° above hori-
zontal. This also caused loss of signal
from plume concentrations near the
ground. Remaining clutter that was sta-
tionary was mapped by the radar when
the chaff was absent (some clutter due to
aircraft and surface vehicles had to be
removed at program operator discretion).
In the affected cells, the signal was kept
only if it was at least 10db (a factor of 10)
stronger than the mapped ground clutter,
or if it showed a doppler speed above a
value set for each averaging period, using
the fact that uncontaminated plume
returns have speeds near u.
Chaff could not be considered a con-
servative tracer because of the large
dropout of chaff clumps in the first few
hundred meters downwind and signifi-
cant surface deposition after the point of
ground contact (in some runs, the inte-
grated plume signal, jfjfXdydz, declined as
much as 50% in the distance interval 1 to
3 km). The estimation of equivalent X/Q
for conservative tracer was done in the
same way as for oil fog, by replacing Q
with ufjfXdydz evaluated at each mean
downwind distance. This estimate, of
course, does not correct for distortion of
the vertical concentration profile which is
due to deposition loss and settling.
Tracer gas sampling and gas chroma-
tography analysis is a well established
method for determining conservative-
tracer X/Q accurately (within about
±10%). During the 1983 CONDORS runs,
SF6 was always released a few meters
from the chaff cutter, on the BAO tower
carriage. Freon 13B1 (CF3Br) was re-
leased from the surface, a few meters
from the oil fog generators when they
were also on the ground. The gases were
stored in compressed gas cylinders and
piped through linearized mass flow
meters to the release nozzles, with strip
charts recording release rates and digital
readouts of total release volume. The
release volume reading was checked
against before and after weights of the
gas cylinders.
Each sampler box contained 12 two-
liter sample bags, each with its own pump
and intake tubing. A remote switch
connected by wire to the line of samplers
initiated the sequential 10-minute sam-
pling for each 120-minute run. After each
run the sample bags were collected by a
person who had not been near the release
points, to avoid contamination. The bags
from each sampler were labeled and
packed into separate 12-compartment
boxes for shipment to Idaho Falls for
analysis. The samplers were analyzed in
the laboratory by use of electron capture
gas chromatographs(GCs). Careful check-
in and handling procedures were fol-
lowed, with calibration of the GCs with
reference gas mixtures before and after
each analysis shift. Repeatability tests
and independent audits of reference gas
mixtures suggest total errors in measured
plume X/Q of less than 10% for SF6.
However, uncertainty in 13B1 measure-
ments was much greater because plume
concentrations were of the same order as
the GC threshold noise levels.
Several months after the field work, in
spite of many precautions, 3/8 of the SF8
samples and 7/8 of the 13B1 samples
were discovered to be severely contami-
nated. After many months of investiga-
tions it was determined that (1) contrary
to instructions, partly filled gas cylinders
were returned to Idaho Falls in the same
truck compartment with the last three
days' samples, (2) that all gas cylinder
valves leak to some extent, and (3) that
clean sample bags stored in the truck
with gas cylinders do become contami-
nated at the high levels that had been
measured (100 to 1000 times expected
plume concentrations). Later, it was
found that the contaminating gas does
not penetrate the bags, but resides on the
lead-in tubing attached to the bags. Four
days of the remaining 13B1 samples
were also contaminated. No proof of
cause was discovered, but the bags
probably were stored near some leaky gas
cylinders at the BAO just prior to use. The
remaining five days of SF6 samples
showed no evidence of contamination
except for occasional "spikes" of high
concentrations at individual samplers,
sometimes recurring several times among
the 12 sequential samples from a run.
This spiking occurred in about 3% of the
SFe samples and remains unexplained.
Meteorological Measurements
As for any diffusion field experiment,
good meteorological measurements were
vital to the success of CONDORS, both
from the operational and the scientific
analysis viewpoints. It was particularly
helpful to go beyond the limitations of
past field experiments in measurement of
variables important to convective turbu-
lence and diffusion, especially z, and w*.
The BAO meteorological tower provided
an excellent starting point. It is equipped
with three-component sonic anemom-
eters, propeller vanes, platinum wire and
quartz thermometers, and dew point
hydrometers at eight levels: 10, 22, 50,
100,150, 200, 250, and 300 m AGL It
has been operated more-or-less continu-
ously since 1980 with real-time logging
of 20-minute averages, including vari-
ances and covariances of wind speed
components and temperature. During
CONDORS runs, the tower data were
logged m fast response modes so that
many types of statistical analyses could
be made at a later date. For instance,
immediately after the experiments, 5-
minute averages of wind speeds, direc-
tions, and w'T' were calculated to help
define optimum averaging periods that
avoid large changes in these variables. To
reduce bulk, much detailed statistical
information for the selected 1983 averag-
ing periods was processed but not in-
cluded in the data report, including mo-
ments of vertical velocity (w,w2, and w3),
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individual and joint distributions of 10-
seconds average horizontal and vertical
wind directions (8, and 6,), and u, 0«, and
^distributions conditionally sampled dur-
ing negative 10-seconds w events.
While the tower provided quite detailed
meteorological information for the lowest
300 m, the experiment required some
information up to z = zi and somewhat
beyond. This was provided mostly by
rawinsondes, which were released near
sunrise and at least twice during each
run. In 1983, a release near 1000 MST
was added to help track z, development
and to check upper level winds for
possible changes in expected midday
winds in the mixing layer (as zi grows,
momentum from the entrained air is
mixed downward). The rawinsondes were
tracked by double theodolite to about
3000 m AGL so that wind speed and
direction profiles, as well as temperature
and humidity profiles, were obtained.
Additional meteorological information
included solar insolation at the surface
and acoustic sounder records.
A summary of important meteorological
and source information for each averag-
ing period is given in Table 1. Periods
were numbered separately in the 1982
and 1983 experiments. Start times were
Mountain Standard (MST), which was,
fortuitously, extremely close to true solar
time at the BAO. Averaging period dura-
tions were usually 30 to 50 minutes.
limited by rapid changes in wind or Zior, in
a few cases, by breaks in chaff or oil fog
releases. For convecti ve experi ments, the
most critical measurement is the mixing
depth, Zi. For 1982 periods, this was
determined entirely from the chaff /Xdy
profiles at x > 2 km by a "zero projection"
method. Oil fog detection did not extend
far enough in 1982, but this method was
applied to 1983 oil fog jXdy profiles. A
second method using JXdy vertical pro-
files of oil fog and chaff was also used in
1983; it set zi as the height of dropoff to
40% of a peak or plateau value in the
upper half of the profiles. Rawinsonde
measurements of virtual potential tem-
perature, dew point, and wind velocity
profiles and lidar measurements of haze
dropoff heights provided additional indi-
cators of zi. Using a consensus of these
estimates, the accuracy of the 1983 z\
estimates is thought to be ±20 m to ±50
m. The convective scale velocity (w*)
depends only on the 1 /3 power of Zj and
w'T'. The latter quantity was taken as the
average of the 10- and 22-m level tower
measurements; at higher levels it tended
to be erratic. The mean wind speed and
direction (u and 0a) were taken as the
average of the upper four levels of sonic
anemometer measurements. Based on
past meteorological experiments, this is
believed to represent well the whole
mixing layer from 0.1 to 0.9 zi (wind
velocity shear was very slight or negligible
above 100 m during CONDORS runs).
An underlined release height for oil fog
or chaff in Table 1 indicates that the
remote sensor data were processed for
that period. SF« heights are listed only for
uncontaminated periods; 13B1 X/Q is
available only for period 1-83. The last
column shows the ratio of source height
(z,) to zi for the elevated release, if there
was one. The post-experiment estimates
of zi show that the experimental targets of
z,/zi — 1 /4 or 1 /2 were usually missed.
However, the groupings of periods near
z,/zi = 0.17,0.33, and 0.43 make possible
the combination of periods to achieve
better ensemble averaging for elevated
sources. For surface sources, data from
all periods can be combined in terms of
the dimensionless convective scaling
coordinates z/zi, y/z(, and X = (x/u)w*/zi.
Weighting of the periods can be done
using absolute duration or durations
normalized by zi/u, which typifies the
passage time of individual convective
eddies.
Data Reported
Although the final report gives detailed
explanations of the CONDORS experi-
ment planning, siting, instrumentation,
operating procedures and processing
methodologies, it is primarily a data
report. Consequently, the bulk of the final
report consists of tables and figures—
approximately 230tables and 240 figures.
This quantity of information can hardly be
summarized, but a reasonably complete
Table 1. Meteorological Measurements and Source Summaries for CONDORS A veraging Periods
Period
Number
0-82
1-82
2-82
3-82
4-82
5-82
1-83
2-83
3-83
4-83
5-83
6-83
7-83
8-83
9-83
10-83
11-83
Month/
Day
9/10
9/16
9/16
9/18
9/20
9/20
8/27
8/28
8/28
8/31
9/06
9/06
9/06
9/07
9/07
9/13
9/13
Start
Time
1143
1304
1411
1354
1153
1312
1330
1130
1230
1055
1050
1130
1210
1230
1310
1140
1240
Duration
(min)
36
29
35
40
44
42
30
30
60
50
40
30
30
40
40
30
40
/,
(m)
1000
520
730
960
980
1260
1600
1240
1400
1100
880
880
880
640
780
900
870
w*
(m/s)
2.07
1.46
1.43
1.54
1.81
1.82
2.00
2.01
1.99
1.88
1.64
1.74
1.65
1.38
1.48
1.80
1.86
u
(m/s)
3.65
5.80
6.23
2.76
2.40
1.59
3.15
1.91
2.57
1.90
2.52
2.59
3.34
4.45
4.59
2.09
1.57
&
Ideg)
114
52
50
89
52
59
121
117
107
127
122
140
122
91
87
102
56
w'T'
tm°C/s>
0.271
0.186
0.124
0.117
0.186
0.148
0.158
0.207
0.179
0.189
0.152
0.184
0.158
0.130
0.133
0.200
0.227
Source Height (m)
Oil
sfc
235
235
167
sfc
sfc
sfc
sfc
sfc
sfc
280
280
280
265
265
sfc
sfc
Chaff
sfc
235
235
167
sfc
sfc
265
235
235
280
280
280
280
265
265
235
235
SFe
—
—
—
—
—
265
235
235
280
280
280
280
265
265
—
—
Za/Zi
.
0.45
0.32
0.17
—
—
0.17
0.19
0.17
0.25
0.32
0.32
0.41
0.41
0.34
0.26
0.27
-------
description of it can be given. This de-
scription will be done in the following
order, representing an increasing amount
of informational detail reported: meteoro-
logical parameters, gaseous tracers,
chaff, and oil fog.
The basic meteorological parameters
reported for each averaging period have
been repeated in this project summary in
Table 1, exceptf or the derived parameters
u/w* (shows degree of convectiveness),
ZjG/w* (length scale for transport dis-
tance), and period duration times u/z,
(dimensionless duration in terms of "eddy
passage time"). Detailed listings of 1983
zi estimates are given in the final report to
show the consistency of differing meth-
ods; the nine types of estimates never all
agree, but, in each period, at least several
methods give approximately the same
value. Finally, some examples of the
statistical information available for 1983
periods are given, namely, actual distri-
butions of 10-s average wind azimuth
and elevation angles, by 5° bins, for z =
250 m. Most of the azimuth distributions
are approximately Gaussian, but most
elevation angle distributions are skewed
strongly toward negative values. Much
more statistical information was pro-
cessed but was too bulky to be included;
the same is true of the 5-minute averaged
tower measurements and the rawinsonde
profiles.
Essentially all of the processed results
of the 1983 gaseous tracer sampling,
except for the highly contaminated runs,
are included in the final data report. Basic
information includes the range and azi-
muth of each sampler from the center of
the BAO tower and the average release
rate(s) of the two gases for each usable
run. The rest of the information concerns
measured X/Q values, the ratio of con-
centration to release rate. In the final
report tables are given for every 10-
minute sample of X/Q at each sampler for
each entire two-hour run that was not
contaminated (one run for 13B1, five runs
for SF8). However, a small fraction of such
samples are missing due to sampler
inoperation. Two tables of averaged X/Q
for the chosen averaging periods are
presented: one with all the available 10-
minute averages and one with "spikes"
of anomalously large X/Q values re-
moved. These spikes are identified in two
tables, one listing multiple spikes at a
single sampler (exceeding both back-
ground and the averaged two neighboring
samplers by at least a factor of 5) and one
listing especially large single spikes (ex-
ceeding both background and the aver-
aged two neighboring samplers by at
least a factor of 10). A figure is shown for
the frequency of occurrence of X/Q
values during each run; this was used to
set "background," or noise level, values.
There are also figures for each usable
1983 averaging period showing average
X/Q values, both with and without spikes,
versus azimuth position of the samplers.
The basic information for the radar/
chaff results includes the Cartesian grid
range and increment chosen in process-
ing each period, the direction chosen for
the x-axis, and the velocity chosen for
thresholding out return signals contami-
nated with ground clutter. Then chaff
plume statistics are presented in tables
for each processed averaging period as
functions of x, mean distance downwind,
incremented by 250 m or 300 m. Statistics
include y and z, a> and az (standard
deviations), the y of maximum /Xdz and
the z of maximum /Xdy, the value of
maximum/Xdy, and JJXdz. An appendix to
the final report shows plots of each of
these quantities (except y) versus x in 50-
m increments. It also shows normalized
/Xdy or /Xdz versus z or versus y and
versus x, in semi-tabular form, for each
processed averaging period; x is usually
in 250-m increments. Finally, a time
history of the contour /Xdz = 100 fila-
ments/(50 m)2 versus x and y is shown
for selected periods from 1983.
The basic information presented for
the lidar/oil fog results, besides specifics
on the lidar and laser beam, consists of
logs of release and scan periods. Then oil
fog statistics for each lidar azimuth are
presented for each processed averaging
period. Statistics include the mean dis-
tances from the source and from the
tower base (when used as a surface
source, oil fog was released 134 m west
and 44 m north of the tower), the corre-
sponding mean azimuth angles,
-------
Lidar and Oil Fog. Both the lidar and the
oil foggers performed well, with only a
few very short lapses. A large release rate
was required to produce a plume that
could be distinguished from background
haze at 2 to 3 km downwind in convective
conditions. This goal was marginally
achieved in 1983 by switching to a very
heavy oil and adding a second fogger for
the surface releases. The paraffin type oil
used in 1982 apparently evaporated to a
significant degree. The lidar provided very
good resolution of plume scans, but with
limited coverage of azimuths.
Samplers and Gases. The single sam-
pling arc with 5° azimuth spacing pro-
vided adequate "ground truth" in this
experiment to test the X/Q assumptions
applied to the observed distributions of
chaff and oil fog, which are not conserva-
tive tracers. The loss of more than half the
data due to contamination was unfortu-
nate and avoidable, in retrospect. Sample
bags should not have been stored near
source gas cylinders, especially in an
enclosed space, because the common
type of cylinder valves do leak slightly.
The contaminated samples could have
been saved had the discovery been made
in time that the contaminating gases
resided only on the intake tubing, not
inside the bags. At any rate, the 1381 gas
released from the surface was inadequate
because the concentrations at the sam-
pling arc were of the same magnitude as
the QC threshold noise levels. The SF6
gas released from the tower was ade-
quate and provided five runs of useful
data.
Tracer Comparisons. As already men-
tioned, with collocated releases the chaff
plumes generally tended to sink lower
than the oil fog plumes, to the expected
degree, due to gravitational settling.
However, the horizontal patterns of/Xdz
tended to agree very well. Several litera-
ture references also compared SF6 with
the lowest layer oil fog X/Q at the azimuth
nearest the sampling arc for period 9-83,
finding disagreement on the location of
plume boundaries and peak by only about
1° of azimuth, or 20 m. The/(X/Q)dy of
the oil fog was only 16% larger than that
of SF6; this is very satisfactory considering
the difference in methods and the inexact
coincidence in space.
Preliminary and partial analysis of
selected periods from both 1982 and
1983 lead to the following tentative
conclusions about diffusion in convective
conditions (WD stands for the convective
tank experiments of Willis and Deardorff):
Plume Width and Depth. The final data
report shows that ffi/z, vs. X = (x/u)w*/zi
for period 9-83 (an example) is in very
good agreement with WD for both oil fog
and chaff measurements. On the other
hand,
-------
J. C. Kaimal, W. L Eberhard, W. M. Moninger, J. E. Gaynor, S. W. Troxel.
and T. Uttal are with the NOAA/ERL Wave Propagation Laboratory, Boulder,
CO 80303; G. E. Start is with NOAA/ERL Air Resources Laboratory, Idaho
Falls, ID 84301; and Gary A. Briggs (also the EPA Project Officer, see below),
is with Atmospheric Sciences Research Laboratory, Research Triangle Park,
NC 27711.
The complete report, entitled "Project CONDORS—Connective Diffusion Observed
by Remote Sensors," (Order No. PB 86-222 221 /AS; Cost: $28.95, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-86/040
0000329 PS
AGENCT
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