5. PLANETARY BOUNDARY LAYER OBSERVATIONS

The boundary layer component of SGP97 is configured to primarily evaluate the influence of soil moisture on the local surface energy budget and the influence of mesoscale variability in the surface energy budget on the development of convective boundary layer. To the extent possible, attempts will be made to quantify the water vapor budget of the boundary layer (advection, entrainment, and evapotranspiration) using remotely sensed and in situ data.

5.1. Water Vapor Profiles

Aboard the Wallops P-3 aircraft together with ESTAR, the NASA Langley Research Center (LaRC) instrument, Lidar Atmospheric Sensing Experiment (LASE), will provide observations of atmospheric water vapor and aerosol profiles, and locations of cloud top along the flight track. The LASE instrument is a compact and highly engineered differential absorption lidar (DIAL) system that has completed its development and validation aboard the high-altitude ER-2 aircraft (Higdon et al., 1994; Browell et al., 1996); the lidar parameters are given in Table 7.

Differential Absorption Lidar (DIAL) is an active remote sensing technique that takes advantage of the absorption of the pulsed laser light along the beam direction to obtain the concentration of the molecular species that causes the selective absorption. In practice, two laser pulses are transmitted near simultaneously one at the peak of the absorption line called the "on-line" and another in the wing of the absorption line called the "off-line". An illustration of the DIAL principle is given in Figure 21. If P_on and P_off denote power received "on-line" and "off-line", respectively, the average molecular number density between ranges R₁ and R₂ is calculated using the relation:

The advantage of the DIAL method is that it can be used to obtain range-resolved profiles of atmospheric gases with high vertical resolution. In addition to measuring gas concentration profiles, high spatial resolution aerosol backscattering distributions are simultaneously obtained as part of the DIAL measurement using the off-line lidar signals. DIAL offers the advantage of adjusting vertical and/or horizontal resolution by averaging the lidar data that are collected at a very high resolution. With the DIAL method, lidar measurements can be made during day or night and between and above cloudy regions in the atmosphere.

In the current mode of operation LASE operates locked to a strong water vapor line and electronically tunes to any spectral position on the absorption line profile. This permits the choice of suitable absorption cross-sections for optimum measurements over a wide range of water vapor concentrations in the atmosphere. In addition, electronic tuning allows the system to rapidly take data over two or three water vapor concentration ranges. This unique method of operation permits rapid and flexible absorption cross-section sampling capability and provides water vapor measurements over the entire troposphere on one aircraft pass. This new method of using two water vapor absorption cross-sections from a single water line (one on the line center and one on the side of the line) was implemented and tested during the LASE validation experiment in September 1995; the intercomparison with a number in situ and remote sensors from the ground and other aircraft demonstrated the accuracy, reliability, and dynamic range of LASE measurements.

The LASE system has been developed as a precursor to a space-based DIAL instrument, and has operated autonomously from the ER-2 aircraft. Several modifications are being made in order to deploy LASE aboard the P-3 aircraft during SGP97; the projected capabilities are listed in Table 8. The projected performance (random error profiles, representing the precision of the water vapor measurement) of LASE aboard P-3 is compared with the LASE capability from the ER-2 in Figure 22.

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An upgraded computer system is planned to support on-board LASE monitoring, data processing and analysis; the post-processing will be used to produce analysis products more refined than is possible with the real-time processing. The on-board data display will provide real-time information concerning the development of the convective boundary layer via images of lidar backscatter. These observations can be used to guide the flux aircraft with regard to choice of flight altitudes and the location of interesting mesoscale features.

5.2. Airborne Fluxes

Two research aircraft will be deployed for the measurement of eddy fluxes of momentum, latent and sensible heat, and other scalars, along with the measurement of mean thermodynamic variables and various radiative components; one is the Twin Otter from the National Research Council Canada (NRCC), and the other the Long­EZ airplane from the NOAA Atmospheric Turbulence and Diffusion Division (ATDD). The scientific objectives, types of flight tracks, and a summary of some survey flights are discussed below, which are followed by a description of the capability and instrumentation of the Twin Otter and Long­EZ aircraft.

5.2.1. Scientific Objectives

The numbers in parentheses are referenced in Table 9 subsequently.

(1) Moisture budget/LASE.

Attempts will be made to construct an atmospheric moisture budget by monitoring the soil moisture and growth of the boundary layer over the P3 domain. The LASE will delineate individual entrainment events and a cross­section of the atmospheric moisture field. This data will be combined with the atmospheric winds to study moisture transport. If feasible, a special attempt may be made to coordinate passage of the P3, Long­EZ and Twin Otter along the same flight track over a specified point at a specified time. The purpose of this coordinated flight is to examine the structure of individual entrainment events with LASE and in situ turbulence measurements. However, the normal mode of operation will not attempt time coordination and the LASE statistics describing the boundary­layer top will be compared with moisture statistics and fluxes collected by the flux aircraft.

(2) Morning transition

The morning boundary­layer transition following the breakup of the nocturnal surface inversion is one of the least understood boundary­layer situations. Failure to correctly model this transition can lead to errors which persist throughout the day. As the boundary layer grows into the unstratified (or weakly stratified) residual layer, boundary­layer growth accelerates. Large downward entrainment of dry air may result. This period has largely been ignored because fluxes are difficult to assess in nonstationary situations and the growth of the boundary layer during this period is sensitive to spatial variations. The LASE backscatter can document horizontal variations of the boundary­layer top and the water vapor measurements may be useful as a tracer for rapid entrainment events. When available, the aircraft data will be combined with tower data to form a more complete picture of the complicated temporal­spatial variations during this period.

(3) Surface moisture gradient

Horizontal gradients of soil moisture lead to spatial gradients of the surface heat and moisture fluxes. With weak wind conditions, the influence of strong variations of surface moisture on sufficiently large scales may extend throughout the boundary layer. In such cases, the boundary layer will be deeper over dry regions. The influence of soil moisture gradients on smaller scales will be limited to the lower part of the boundary layer below the "blending height". With strong winds, the blending height is closer to the surface and the vertical influence of the surface heterogeneity is more limited. Vertical integration of the LASE water vapor may be used to assess the horizontal variation of the boundary­layer moisture.

While the influence of the surface soil moisture gradient is expected to be greatest during the morning transition period, the influence of spatial gradients may be difficult to isolate with aircraft data because of the large nonstationarity. Therefore, the initial aircraft studies will concentrate on the transition over homogeneous regions. The P­3 flight period is expected to span the morning boundary layer transition when the influence of soil moisture on boundary­layer development should be most noticeable. The combination of simultaneous soil moisture and boundary layer depth and water vapor measurements from ESTAR and LASE will be used to document the influence of soil moisture variability on morning boundary­layer development.

(4) Wing to wing/ tower comparison

Intercomparisons between the two flux aircraft are necessary since they will be flying simultaneously at different levels in order to examine the vertical structure of the boundary layer.

(5) Mid­day studies of the boundary layer structure.

During the middle of the day and early afternoon, the boundary layer growth is reduced and the boundary layer often reaches near­stationary conditions. This period has been studied in numerous previous field programs and allows comparison of the SGP boundary layers with those in other regions and different seasons. Although the entrainment flux is normally smaller during this period, it is more stationary and easier to sample. These are the simplest conditions under which to test the ability of ESTAR and LASE to observe the boundary­layer moisture budget. The P­3 will hopefully encounter such conditions towards the end of its scheduled flight time.

(6) Evening transition period

This transition period has also been neglected in almost all previous field programs. The details of the early evening transition period may influence the strength of the nocturnal jet and structure of the nocturnal boundary layer and may determine whether the nocturnal surface is characterized by condensation (weak jet and shallow nocturnal boundary layer) or by continued evaporation (windy deep nocturnal boundary layer). One of the goals of this study will be to examine the decay of the fossil turbulence in the residual layer.

5.2.2. Types of Flight Tracks

Three types of tracks (Table 9) are considered for the Twin Otter (TO) and Long­EZ (LE). Standard tracks may assume either a straight line or an L­pattern of repeated passes. Soil moisture (SM) gradient tracks refers to longer tracks along Wallops P­3 tracks which will be used when there is a strong gradient or contrast in surface soil moisture conditions. Tower tracks are used for intercomparisons between aircraft and flux stations or towers. Aircraft soundings will be interspersed throughout deployment as appropriate especially during flights for boundary­layer morning transition.

5.2.3. Summary of Survey Flights on May 4, 1997

The flight tracks described below and plotted in Figure 23 were surveyed on May 4, 1997. The choice for flight tracks will be discussed during daily aircraft briefings and reviewed next morning.

(1) Long segment of P­3 Line 2, AS­AN

­ A good track in general, with mostly winter wheat, some cattle, and the usual hydro lines.

­ Only real obstruction is the town of Fairmont 18.9 miles DME south of AN, which lies right on the track. Suggest a diversion a mile or so east (i.e., away from Enid Airport).

­ Near AN there is a line of trees just south of the Fork River that makes a good visual reference to terminate the line.

­ Must call Vance Control northbound on this track.

AS 35 42.5 97 53.0 AN 36 39.5 97 36.7

(2) Long segment of P­3 Line 3, BS­BN

­ A very good track, mostly winter wheat and few cattle.

­ one large 420 ft tower near track (approximately 35 59.0 97 41.0).

­ Also there is a gas processing plant 5.3 n miles north of the south waypoint BS that must be diverted around.

­ The town of Covington (near 36 18.5 97 35.0) lies just east of the track, with a small airport just west of town and close to the track. Should shade the track to the west here.

BS 35 42.5 97 46.0 BN 36 39.5 97 29.7

(3) ARM site, CS­CN

­ Track looks good, but should fly with a ½ mile offset west or east depending on wind direction (i.e., to stay downwind of their tower facility).

­ The original track ends at a tree line just north of the Fork River. We should probably cut it short to end south of the river

CS 35 25.0 97 29.0 CN 36 40.3 97 29.0

(4) East of Enid, DW­DE

­ The track has been moved 0.4 n miles south.

­ A good track with few houses, becomes a little hilly with trees near the east end.

­ Almost entirely in Vance control zone, so they must be called on approach.

DW 36 12.6 97 47.0 DE 36 12.6 97 26.5

(5) Kingfisher, EW­EE

­ Track was moved one mile north to avoid homes, and eastern waypoint was moved one minute of longitude west. The former common ESW waypoint used for both legs of the 'L' was separated to EW and ES.

­ New track looks very good, but FAA warned us that this is a sensitive area with several expensive horse paddocks.

EW 35 46.0 97 52.3 EE 35 46.0 97 33.0

(6) Kingfisher, ES­EN

­ The track was moved about a ½ mile east to place it between the north/south roads.

­ This is a good track, mostly winter wheat with a few homes scattered near the north end.

­ North end is in Vance Control area, so they must be informed prior to entry.

ES 35 45.0 97 51.7 EN 36 02.0 97 51.7

(7) Chickasha, FS­FN

­ The original FS waypoint was a bit close to a lake and the line was aligned too close to a

north/south road. We moved the line to the east, to the following waypoints:

FS 35 07.8 98 05.0 FN 35 24.0 98 05.0

­ The terrain rises in the north half of the track, becoming a little hilly with some forest. It might be advisable to pick a new line here running SW/NE in the flatter part of the area, for example:

FW 35 09.0 98 17.0 FE 35 16.0 98 0.0

­ Watch out for 200­300 ft towers in the turning areas at each end of this new track

(8) Washita, GS­GN

­ The north half of this track was best, as there was a built­up area 10.9 n miles south of GN, and a small airstrip 12 miles south of GN.

­ Track ended up passing about ½ mile east of Tilden Meyer's tower, which is at 34 57.62 and 97 57.70. This may have been just a navigational drift right of track, or perhaps we do not have the exact location of the tower.

­ Could extend track to north about another mile to approximately 34 58.6 and 97 57.7

­ Could also move southern waypoint GS to the west to avoid the conflicts identified above and to stay out of Shepherd 2 MOA; Of course, this may result in other problems, so the new track will have to be test flown.

­ The lats and longs for the new suggested track follow. This track end up paralleling a segment of the third P3 line, and within one mile to the east. Watch out for 390 ft tower northwest of the new GS.

GS 34 42.0 98 02.0 GN 34 58.6 97 57.7

(9) Washita, GW­GE

­ Track as originally planned is no good ­ the town of Cement sprawls right across the track, and there is an above average amount of forest on the track, making it rather atypical of the general surroundings. We picked a new western waypoint that provided a clearer run over what was probably mostly winter wheat. This track will start just east of a north/south hydro line and then pass south of the town of Cyril to end at the original GE.

­ Most of the track is still in the Washita MOA

GW 34 50.0 98 15.7 GE 34 57.2 98 02.0

(10) El Reno, RW­RE

­ Line looks very good. A few cattle, mostly at east end which is probably part of the federal land. There are a couple of homes near the track 6.6 n miles west of RE (approximately 35 32.83 and 98 11.4), and it might be wise to inform these property owners about the low­flying aircraft.

RW 35 32.83 98 13.01 RE 35 32.83 98 03.28

5.2.4. Participating Aircraft

5.2.4.1. NRC Twin Otter

The NRC Twin Otter atmospheric research aircraft is a twin-engine turboprop STOL transport with a gross takeoff weight of 11579 lb. Without the use of a supplementary oxygen system, it has a service ceiling of 10,000 feet and an endurance of about 3.5 hours (depending on installed instrumentation). In its trace gas flux-measuring role, the aircraft is flown at about 105 knots (55 mps) and can operate at altitudes as low as 100 feet. Research flights are usually flown with a crew of four.

Configured for flux measurement, the basic instrumentation aboard the aircraft measures the following:

* the three orthogonal components of atmospheric motion.

* the vertical fluxes of sensible and latent heat, momentum, turbulent kinetic energy, CO2 and ozone.

* concentrations of CO2, H2O and ozone.

* atmospheric state parameters such as pressure, temperature, dew point, and mean winds.

* aircraft position (GPS), motion and attitude (Litton-90 Inertial Reference System), pressure height, and height above ground (radio-altimeter, laser altimeter).

* radiometric surface temperature, incident and reflected solar radiation, net radiation, greenness index (NDVI), 4-channel satellite simulator (Landsat or SPOT).

* VHS videotape using under-nose and side-looking cameras with superimposed listing of time, altitude, heading, latitude and longitude.

Data are recorded digitally on DAT tape at a rate of 32 Hz, after anti-alias filtering at 10 Hz, giving an along-track resolution of about 5 meters at the usual flux measuring speed of 50-55 mps. Winds and estimated fluxes are computed in real time by the aircraft's VME-based computer system, with results immediately displayed to the cockpit and cabin crew. This allows the crew to assess the state of the boundary layer, or recognize instrumentation problems, and modify the flight plan as required.

Along with aircraft spares and maintenance equipment, a full data playback facility is transported to the field site, and is usually set up in a meeting room in the crew's hotel. Within a few hours of landing, collaborating scientists can have access to the analyzed data, which includes run-averaged fluxes, analog traces, flight tracks, videotape, tephigrams from soundings, spectra and cospectra of flux contributions. A review of these data allows scientists to compare the measurements with expectations and with data from other sensing platforms, and thus make decisions on the scientific direction of subsequent flights.

After the completion of the field phase of the experiment, the data are re-analyzed, applying adjusted calibrations, and correcting the measured horizontal wind data using a Kalman-filtering technique, which removes small drifts present in velocity measurements from inertial navigation systems. The run-averaged results and all 32-Hz data (approximately 160 variables) are archived on optical disk. At the request of collaborating scientists, these files can be accessed at a later date to strip off time histories of a selection of parameters, which are then electronically transferred by ftp. For this project, run-averaged data could also be archived in the format used in the BOREAS project and already stored at NASA. Finally, about six months after completion of the field experiment, NRC will produce a project report, which will include a description of the instrumentation used, a summary of all the flights, data presentations and preliminary analyses related to the objectives of the experiment. An example of the report from the 1994 BOREAS project is available upon request.

Further details on the Twin Otter and its instrumentation are available in MacPherson (1996), MacPherson and Bastian (1997), and MacPherson, Grossman and Kelly (1992). The following websites can also be accessed: http://www.iar.nrc.ca/iar/fr_otter-e.html and the 'measurement network' and 'database' sections of http://www.cmc.ec.gc.ca/rpn/mermoz.

5.2.4.2. ATDD Long-EZ

The Long­EZ flux aircraft, N3R, is an experimental airplane; with its wide body and higher power, it is more capable than the standard Rutan Long­EZ, a two passenger high performance canard airplane. Its aerodynamic characteristics have many advantages for high­fidelity turbulent flux measurement. The small, laminar­flow airframe has an equivalent flat plate drag area of 0.2 m², minimizing flow distortion at the nose for high­fidelity measurements of winds, temperature and trace species. The pusher configuration leaves the nose free of propeller­induced disturbance, engine vibration, and exhaust. The canard design resists stalling and has excellent pitch stability in turbulent conditions. This, combined with its low wing loading, allows for safe low­speed (50 m s^-1), low­altitude (10 m) flux measurement. For enhanced safety, the Long­EZ is equipped with a ballistically­deployed safety parachute (deployment requires 0.9 s).

The Long­EZ has an empty mass of 430 kg and a maximum gross takeoff mass of 800 kg. Endurance significantly exceeds 10 hours, although pilot fatigue precludes routine 10­hour missions. Typical operations include two 4­hr or three 3­hr missions. The small size allows operation from relatively small airports, though requiring at least 1000m of paved runway.

The airborne flux instrumentation, and the data system with its associated software were specifically designed and built by ATDD (Crawford et al., 1990). Wind velocity and temperature fluctuations are measured with ATDD's turbulence probe (Crawford and Dobosy, 1992). The probe is mounted five chord lengths ahead of the wings, where flow distortion is small (Crawford et al., 1996). It carries pressure, temperature and acceleration sensors in a nine­hole pressure­sphere gust probe of ATDD design. This sensor suite is specifically designed for eddy­flux measurement at the higher frequencies required for low altitude flight. A thermistor in the central pressure port provides simultaneous temperature measurement, at a location symmetrical with respect to the flow, for accurate determination of true air speed and heat flux. Water-vapor and CO₂ fluctuations are measured with an open­path, infrared gas absorption (IRGA) analyzer, developed at ATDD (Auble and Meyers, 1992). This sensor responds to frequencies up to 40 Hz, has low noise and high sensitivity (for CO₂, 20 mg m^-3 v^-1). The sensor is rugged and experiences little drift.

A unique difference in the Long­EZ instrument system is its pioneering use of a mix of differentially-corrected GPS and integrated acceleration measurements to determine position, velocity, and platform attitude. Differential correction of GPS involves determining the position or velocity as a relative quantity, the difference between values at two receivers. Many GPS errors are common to all receivers in a given area and are canceled when the measurements from two separate receivers are subtracted. The receivers we use report position, velocity and attitude ten times per second. To obtain this information at higher frequencies we integrate acceleration measurements. By adding filtered signals (high pass for integrated accelerations, and low pass for GPS) information on position, velocity, and attitude of the Long-EZ can be obtained over the same range obtainable from a high-quality inertial navigation system (INS).

The data stream is dominated by high­frequency analog signals from the accelerometers, pressure sensors and the like. Analog signals are first electronically conditioned by 30­Hz lowpass Butterworth anti­aliasing filters. The conditioned signals are then sampled and digitized at 250 Hz. The 250­Hz data are digitally filtered and sub­sampled to 50 Hz. Although several other data frequencies are being written to disk, all are synchronized to a single clock frequency. Spectra and cospectra data analysis show that the 50­Hz flux data rate is adequate for measuring fluxes at the Long­EZ flight speed and altitude. The final, meteorologically relevant quantities from Long-EZ are listed in Tables 11 and 12.

5.3. Surface Flux Measurements

5.3.1. Participants

In addition to the ARM surface flux stations within the SGP study area, there will be a group of investigators collecting surface flux and ancillary meteorological data during the SGP intensive field campaign. These are summarized below:

NASA-GSFC/Univ of Arizona

The Univ of Arizona Eddy Correlation system measures the 3D wind vector with a weather resistant Solent sonic anemometer, and concentrations of CO2 and H2O using a Li-Cor 6262 infrared gas analyzer at 20 Hz. All the raw data is saved, and processed at a later time on a PC (but a real­time first guess is possible). Supporting measurements are standard met variables measured with a Campbell weather station: wind speed and direction, relative humidity, air temperature, solar and net radiation, soil temperature, soil heat flux, and rainfall. Plans for deployment are still TBD. The goal is to help validate the ARM EC and Bowen Ratio measurements.

USDA-ARS

The USDA-ARS plans to conduct measurements at three sites within the El Reno facility. The sites will be representative of the three main vegetation cover types: winter wheat, Bermuda grass and natural rangeland/prairie. At each site a Campbell 3D sonic anemometer along with a 1D KH2O for measuring sensible and latent heat fluxes will be deployed. Ancillary measurements will include soil temperature, soil heat flux and meteorological observations: wind speed and direction, air temperature, relative humidity, and net and solar radiation. There are also plans to co-locate a Campbell Scientific Bowen ratio system using the Li­Cor 6262 CO2/H2O gas analyzers at two of the sites. In addition, there are plans to install on a more permanent basis three SHAWMS (Soil Heat And Water Measurement Systems) nearby the flux measurement systems. These systems measure soil heat flux, soil temperatures, soil thermal conductivity and moisture in the root zone (approximately the first 1 m of the soil profile). At the three sites radiometric surface temperatures will be collected on a continuous basis using Everest 4000's.

Univ of Wisconsin

A major focus of this group will be to conduct comparisons between a "roving" eddy

correlation unit (consisting of a 3D sonic and 1D KH2O) and the different instrumentation running at the various flux stations during the SGP study period. Part of this "roving" system, will be a newly purchased Kipp & Zonen CNR-1 net radiometer to compare with net radiometer measurements being made by other net radiometer type(s). This project will help determine which flux stations may be having problems or at the very least showing large discrepancies with the "roving" system. It will also provide a means for reducing variation in net radiation observations caused by differences in net radiometer types/calibrations. They are also planning the installation of infrared radiometers at as many of the flux sites as possible for recording surface temperature on a continuous basis.

JPL

Main interest is to collect surface flux data during aircraft thermal infrared observations and compare eddy correlation measurements using different instrument types with ground-based thermal infrared observations. Instruments include; a Campbell Scientific 3­D sonic and a 1­D sonic system, a couple of KH20 for EC humidity measurements, and about 6­8 fine wire thermocouples that could be used for sensible heat flux estimation via the variance method, a TDR for soil moisture measurements, and about 60 or more soil thermocouples. Will also be able to bring along at least one Everest IR radiometer, about 5­10 CSI data loggers, a profile system with anemometers, thermocouples, and humidity sensors that can be used for estimating surface roughness as well as to compare with the eddy correlation and Bowen ratio systems. Have not decided on a location for his surface flux and ancillary meteorological measurements.

Georgia Tech

Campbell Scientific Bowen ratio system and will be siting the instrumentation with the sounding location in the Little Washita Watershed. The exact location is unknown, but plans are to locate on a pasture site. Measurements include incoming solar radiation, net radiation, ground heat flux and soil temperature, wind speed and direction, surface pressure, air temperature, and relative humidity .

NOAA/AATD

This group has been collecting energy and CO2 flux data on a continuous basis at a rangeland site in the Little Washita. The flux instrumentation includes a 3­D sonic (Gill instruments, model R2) and an ATDD open path H2O/CO2 gas analyzer. Ancillary measurements include net and solar radiation, incoming and reflected PAR, soil temperatures (at 6 levels), ground heat flux, precipitation, surface wetness, surface temperature, air temperature and relative humidity, atmospheric pressure, and soil moisture.

5.3.2. General Plan

The surface flux group will begin the SGP Experiment by conducting a co­location study at the El Reno facility site ER01. At this location there will be an ARM flux station (EF19). The co­location study will be from approximately June 9­15. Table 13 contains a list of the flux sites, description or reference to the flux "team" (name of PI and e­mail is provided) conducting the measurements, the type of measurements, surface type or cover, fluxes being measured and ancillary data being collected. A key following Table 13 describes all the symbols. Note that numbers in parentheses under the column labeled ANCILLARY DATA represent the number of heights/depths of the observations.

Fluxes and ancillary data will be averaged over 30 minute periods and reported in CST (Central Standard Time)

Most flux stations are either "permanent" or will be in one location for the duration of the SGP Experiment (see Table 13). There are some flux stations that will be moved during the experiment (UW EC and NASA/UA EC systems). JPL will have several different flux systems in operation during the experiment covering a number of locations. Table 14 provides a tentative schedule of when and where these flux systems will be.

¹ The NASA/UA EC system will visit flux stations at ER01 and CF02, remaining at either location for approximately 2­3 weeks.

² The UW EC system will visit each EC and BR flux station listed in Table 1 for a 2­3 day period during the SGP Experiment.

³ The EF EC systems have in close proximity of the measurements 3 other ARM platforms: SIROS, SMOS, and SWATS. The SIROS measures upwelling and downwelling solar and infrared irradiances above untilled land. The SMOS measures mean wind speed and direction at a height of 10 m and, closer to the surface, temperature, humidity, barometric pressure, and precipitation The SWATS system measures a profile of soil temperature and humidity.

⁴ SHAWMS systems measuring soil temperatures at 8 depths and soil moisture at 6 depths are located near ER01 (ARS), LW02 (NOAA) and LW11 (GTech).

Key For Table 13.

SITE: LW= Little Washita, ER=El Reno, CF=Central Facility; MARS, KING & ELRE are Mesonet sites

DESCRIPTION: NOAA=Oak Ridge National Labs, Tilden Meyers <meyers@atdd.noaa.gov>; EF= ARM Extended Facility, Marv Wesley <Wesely@anler.er.anl.gov>; GTech= Georgia Tech, Christa Peters­Lidard <cpeters@ce.gatech.edu>; ARS=Agriculture Research Service, John Prueger <midwest@iastate.edu>; NASA/UA=NASA/University of Arizona, Paul Houser <houser@hydro4.gsfc.nasa.gov>; JPL=Jet Propulsion Lab, John Schieldge <john@lithos.jpl.nasa.gov>; UW=University of Wisconsin, John Norman <norman@calshp.cals.wisc.edu>; NSCaRS=Center for Hydrology, Soil Climatology, and Remote Sensing, Chip Laymon <Charles.Laymon@msfc.nasa.gov>

TYPE: BR=Bowen ratio; EC: Eddy Correlation; PR: Profile; VR: Variance

COVER: Range: Rangeland, typically grazed prairie; Wheat: Winter wheat which will be senescent and either harvested or grazed; Grass: Bermuda grass.

FLUXES: Rn=net radiation; Rs=solar radiation; G=soil heat flux; H=sensible heat flux; LE=latent heat flux; U*=friction velocity; CO2=carbon flux

ANCILLARY DATA: U&V =horizontal wind components; W=vertical wind component; U^2, V^2 & W^2 = variances of the wind components; Ta^2=variance in air temperature; WD=wind direction from vane; Ta=air temperature; RH=relative humidity; Press=atmospheric pressure; Precip=precipitation; SM=soil moisture; Tsoil=soil temperature; SW=surface wetness; Tsurf=surface temperature

MISCELLANEOUS INFO: The following EC systems and associated site will be storing their raw 10­20 Hz data: EF14 (CF02), NASA/UA(ER01), NASA/UA(CF02), ARS(ER10), JPL EC (ER01) and possibly NOAA (LW02).

5.4. Tethersonde Program Description

Georgia Tech and National Severe Storms Laboratory (NSSL) will jointly operate a tethersonde in the SGP97 domain to acquire high-temporal and vertical resolution profiles of temperature, humidity, pressure, and wind speed and direction in the lower atmospheric boundary layer.

The tethersonde to be deployed is an AIR-3A system which consists of a meteorological sensor package powered by a sealed 9V alkaline battery and suspended below a gas-filled tethered balloon which is raised and lowered using a heavy-duty winch. The balloon can attain a maximum altitude of 1000 m AGL, and can only be deployed in winds less than 15 knots. Samples can be obtained at a rate of one every 10 seconds, which yields a 10-20 meter vertical resolution in the atmosphere assuming rise rates of 1-2 m/s. The rise rate can be controlled via a manual control dial on the winch.

The sensors include dry and wet bulb thermistors, an aneroid capacitance barometer, a three-cup anemometer with tachometer and a magnetic compass. Humidity is obtained using dry and wet bulb measurements and the psychometric equation. Detailed sensor information is given in Table 15.

The sensor data is transmit by a 10 milliwatt transmitter at a frequency of 403.5 MHZ to the AIR ground station, which post-processes and logs the data. The data can then be easily transferred to a laptop computer for analysis and distribution.

The tethersonde will be continuously operated from sunrise through the late morning hours (approximately 11:00 local time) in order to obtain maximum temporal resolution to study boundary layer growth. It is anticipated that we will obtain two complete (ascending plus descending) profiles per hour during the morning hours. After about 1100 LT the tethersonde will be operated on an hourly schedule throughout the afternoon. The exact location for the tethersonde instrument has not yet been determined.