TITLE: Mesonet ABLE ECOR Data [DOE]
CONTACTS:
Richard L. Coulter - ER 203
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
Voice: 630 252-5833
Fax: 630 252-5498
Email: rl_coulter@anl.gov
1.0 DATA SET OVERVIEW
This data set contains 30-minute resolution eddy correlation (ECOR)
system data from the Atmospheric Boundary Layer Experiments (ABLE)
operated by the Argonne National Laboratory in the Walnut River
Watershed in Butler County Kansas (east of Wichita). The ABLE ECOR
was located at the Smileyberg, KS site during the IHOP period. An
additional moveable ECOR system was located near Brainerd, KS during
IHOP. Data cover the period from 13 May to 25 June 2002. The data
are in ASCII format.
2.0 INSTRUMENT DESCRIPTION
All information included herein is from the ABLE web pages:
gonzalo.er.anl.gov/ABLE/
2.1 General Information
The ABLE Eddy Correlation Flux Measurement System provides in situ
half-hour averages of the surface vertical fluxes of momentum, sensible
heat, latent heat, and carbon dioxide. The fluxes are obtained by the
eddy-correlation technique, i.e. by correlating the vertical wind component
with the horizontal wind component, the sonic temperature (which is
approximately equal to the virtual temperature), the water vapor density,
and the carbon dioxide density. A 3-dimensional sonic anemometer is used to
obtain the orthogonal wind components and the sonic temperature. A folded,
open path H2O/CO2 infrared gas analyzer is used to obtain the water vapor
and carbon dioxide densities.
The eddy correlation system produces 30-minute averages of the surface
vertical fluxes of momentum, sensible heat, latent heat, and carbon dioxide
representative of the pastureland less than 200 hundred meters upwind of
the system. The fluxes are computed from the following directly measured
data.
Orthogonal components of the wind velocity, u, v, and w, are measured ten
times per second in m s-1 by a sonic anemometer. Sonic temperature, which
is approximately equal to virtual temperature, is determined ten times per
second in degrees K by the sonic anemometer from the speed of sound.
Horizontal wind speed is computed ten times per second from the vector sum
of the horizontal, orthogonal winds. Water vapor density and carbon dioxide
density are measured ten times per second by a folded, open path infrared
gas analyzer.
2.2 Components
3-D Sonic Anemometer, Gill Instruments Ltd. Omnidirectional Model R3
Note: all accuracies below are for a temperature range of 5 to 35 degrees C.
Orthogonal wind velocities u, v, and w
Range: +/- 30 m s-1
Accuracy: +/-1% RMS for speed < 30 m s-1, +/-2% for 30 m s-1< speed < 60 m s-1
Resolution: 0.01 m s-1
Wind direction
Range: 0 to 360 deg
Accuracy: same as for speed
Resolution 0.01 deg
Sonic temperature
Range: -20 to +50 deg C
Accuracy: same as for speed
Resolution: 0.01 deg C
ATDD/NOAA H2O/CO2 Infrared Gas Analyzer
Water vapor density
Range: 0 to 30 g m-3
Accuracy: +/-1.0 g m-3
Resolution: 0.01 g m-3
Carbon Dioxide Density
Accuracy: approximately 1 mg m-3
Range: operationally, approximately 50 to 800 mg m-3
Resolution: 0.01 mg m-3
2.3 System Configuration and Measurement Methods
An eddy correlation system is presently deployed at the Smileyberg, KS ABLE
site. Another system is expected to be deployed at another ABLE site in
FY1998. The effective measurement height of the eddy correlation sensors is
2.1 m. Gas analyzer outputs are accepted by the Gill sonic anemometer and
are sampled at the same 10 Hz rate as the sonic measurements. Sampling
synchronization is controlled by the Gill sonic anemometer. The Gill sonic
anemometer outputs all sonic and gas analyzer measurements as a serial data
stream; the data stream is sampled by a VME-based data processing unit (the
same one used to acquire data from the AWS). The VME unit performs all
processing of the eddy correlation data, which is then stored for later
retrieval by a remote UNIX workstation.
The Gill sonic anemometer makes observations of the orthogonal wind
velocities by measuring the travel time of sound with and against the wind
and of the temperature by measuring the speed of sound. The infrared gas
analyzer makes observations of the water vapor density and carbon dioxide
density by measuring the absorption of an infrared light beam. The gas
analyzer analog outputs are low-pass filtered to remove high frequency
electronic noise.
Data analysis is performed by the VME for 30 minute periods. Vertical
fluxes of momentum, sensible heat, latent heat, and carbon dioxide are
determined using the eddy-correlation technique (see Theory of Operation
below). Means, variances, and covariances of the input data are computed
and three-dimensional coordinate rotations are applied. The coordinate
rotations result in zero mean vertical and transverse wind speeds. AWS
meteorological measurements are used to calculate mixing ratio, air
density, specific heat of air at constant pressure, and latent heat of
vaporization of water from the mean water vapor pressure, air temperature,
and barometric pressure. The meteorological measurements and the rotated
covariances are used to compute the vertical fluxes of momentum, sensible
heat, latent heat, and carbon dioxide.
2.4 System Uncertainties
Wind velocities, sonic temperature, water vapor density, and carbon dioxide
density are measured by the sensors and digitally transmitted to the
computer. The sensor accuracies specified by the manufacturers (see List of
Components above) apply to the primary quantities measured. Air
temperature, relative humidity, and barometric pressure measurement
accuracies can be found in the documentation on the AWS; the computed
fluxes have little sensitivity to errors in these measurements.
Interferences may occur within the sound or light paths of the sensors,
e.g. liquid or frozen water, soil, plant matter, and insects. Typically,
these interferences cause a reduction or incease in the signal; if they
occur with sufficient frequency or cause a large enough deviation from the
mean, the flux data will be corrupted. Corruption of half hour values or a
sensor malfunction can sometimes be determined from spectral analysis of
the data.
2.5 Theory of Operations
The Gill sonic anemometer uses three pairs of orthogonally oriented,
ultrasonic transmit/receive transducers to measure the transit time of
sound signals traveling between the transducer pairs. A pair of
measurements are made along each axis ten times per second. The wind speed
along each axis is determined from the difference in transit times. The
sonic temperature is computed from the speed of sound, determined from the
average transit time along the vertical axis.
The infrared gas analyzer measures water vapor density and carbon dioxide
density by detecting the absorption of infrared radiation by water vapor or
carbon dioxide in the light path. Two infrared wavelength bands are used,
centered on bands strongly absorbed by water vapor or carbon dioxide. The
sonic anemometer samples the gas analyzer analog outputs ten times per
second.
Half hour average ambient air temperature, water vapor pressure and
barometric pressure are determined from AWS meteorological measurements and
used in the calculations of the sensible and latent heat fluxes.
Flux and spectra data processing is accomplished with a VME-based computer.
Half hour data files are stored on the hard disk and later retrieved over
phone lines by a remote UNIX workstation.
Momentum flux is determined from the correlation between horizontal and
vertical eddy velocities. The eddy velocities are departures from a
characteristic mean. The appropriate period for this mean is a function of
height. Similarly, the vertical fluxes of sensible heat, latent heat, and
carbon dioxide are determined directly from the correlation between
departures of the vertical velocity and of temperature, water vapor, and
carbon dioxide from their characteristic means.
The characteristic means are estimated from 200 second running means of the
turbulent parameters (the 3 orthogonal components of the wind, the computed
horizontal wind speed, sonic temperature, water vapor density, and carbon
dioxide density). The running means are computed recursively and
continuously updated. Data analysis includes computation of means,
departures of the input data from their means for the analysis period, and
variances and covariances of the departures of the data from the running
means. Three dimensional coordinate rotations are applied to the variances
and covariances. The rotations result in zero mean vertical and transverse
wind speeds.
The mixing ratio, air density, specific heat of dry air at constant
pressure, and the heat of vaporization of water are computed from average
values of water vapor pressure, air temperature, and barometric pressure.
These coefficients are used with the coordinate-rotated covariances to
compute the friction velocity, sensible heat flux, latent heat flux, and
carbon dioxide flux.
2.6 Station Locations
UTM km (Zone 14)
Site 99 deg Meridan DEG dddmmmsss ddmm.mm Alt (m)
----------------------------------------------------------------------------------
Smileyberg, KS 4154.6 UTMN km 37.521 37 31' 15" 37 31.26' 408
689.6 UTME km 96.855 96 51' 18" 96 51.30'
For file names the station IDs are as follows:
Whitewater - sm
Moveable site at Brainerd - ec
Topo maps and aerial photos are available at:
gonzalo.er.anl.gov/ABLE/sitelatlon.html
3.0 DATA COLLECTION AND PROCESSING
See the document ABLE_EC.pdf which is included with your order
for information on the ABLE ECOR data collection and processing
methodologies.
UCAR/JOSS conducted no processing or quality control on these data.
4.0 DATA FORMAT AND FILE NAMING
4.1 Data Format
These data are in ASCII format.
u horizontal wind speed along the north-south axis of a sonic anemometer, in m s-1
v horizontal wind speed along the east-west axis of a sonic anemometer, in m s-1
w vertical wind speed from a sonic anemometer, in m s-1
t sonic anemometer temperature, in degrees C
q water vapor density, in g m-3
CO2 carbon dioxide concentration in micromoles m-3
spd the horizontal wind speed along the wind direction, in m s-1
wind speed the horizontal wind speed along the wind direction, in m s-1
direction wind direction, in degrees
vertical angle angle of the wind to the geopotential surface, in degrees
ustar friction velocity, in m s-1
H sensible heat flux, in W m-2
LvE latent heat flux, in W m-2
4.2 File Naming conventions
ec020513.flx
where:
ec is the station ID (here Brainerd).
02 is the year (2002)
05 is the month (June)
13 is the day of month
5.0 DATA REMARKS
None.
6.0 REFERNCES
ABLE Home Page: gonzalo.er.anl.gov/ABLE/