GCIP/EOP NOAA/ATDD Bondville, Illinois Long Term Flux Site 1.0 General Information During the summer of 1996, a second flux/meteorological system was installed just south of Champaign, Illinois on a farm owned and operated by John Reifsteck (Word Wide Web site is http://W3.ag.uiuc.edu/INFOAG/cyberfarm/reifstck/index/html). This farm (40 00.366' N, 88 17.512' W) is within the GEWEX/GCIP large scale area north central (NC), and just on the northeastern edge of the LSA southeast (SE) region. The site characteristics are typical of those found throughout the midwestern U.S., with most of the land in agricultural production. The soil (silt loam) has a bulk density of 1.5 g/cm3 with sand, silt, and clay fractions of 5%, 70%, and 25%, respectively. The farm has been in continuous no-till since 1986, alternating each year between corn and soybeans. In 1996, the field consisted of soybeans, corn in 1997 and again soybeans in 1998. Corn was planted in 1999 and soybeans will be grown in the year 2000. From measured leaf area index data and measures of visible reflectance, files containing leaf area index information for each day in the growing season have been generated for 1997, 1998 and 1999. These LAI data are included in Section 3.0 below. 2.0 Crop Information Year crop Planting Date Harvest Date --------------------------------------------------------- 1996 Soybeans -- 10/25 1997 corn 04/18 10/19 1998 Soybeans 06/01 10/10 1999 Corn 05/10 10/23 3.0 Leaf Area Index (LAI) Information 1996 ------------------- Date LAI 8/29 5.0 10/25 Harvested LAI data for 1997, 1998, and 1999 are available in separate files and will are included when an order is placed. These files will have as part of there filenames bv97_lai.prn, bv98_lai.prn, and bv99_lai.prn. 4.0 Site Location The site is within 5 km of the NOAA's SURFRAD site, which provides measurements of direct and diffuse shortwave radiation and the incoming and outgoing longwave components. The flux/meteorological system is nearly identical to the Little Washita System with the exception that the instrumentation and solar panels are mounted on a scaffolding tower. Site: Champaign, Illinois (near Bondville) site latitude 40 deg 00.366 min N longitude 88 deg 22.373 min W elevation approx 300 m 5.0 Methodology Traditionally, the use of the eddy correlation method (Businger, 1987; Baldocchi et al., 1988) has been constrained to mainly short term intensive field campaigns. Improvements in instrument design, stability, and powee requirements over the past decade now allow for nearly continuous measurements of sensible and latent energy fluxes using the eddy covariance technique. Using this technique, the average vertical turbulent eddy fluxes of sensible and latent heat (and other scalars) are determined as ____ w'X' = $(w-{w})(X-{X}) --------------- n where w is the vertical velocity component of the wind vector, and X is the scalar of interest (e.g. water vapor concentration). Here, the {bracketed} quantities denote an average or "mean" that is subtracted from the instantaneous values to obtain the fluctuating component. The $ represents the summation from i = 1 to n. Average vertical turbulent ____ fluxes (w'X') are computed in real time using a digital recursive filter (200 s time constant) for the determination of a running "mean" from which the instantaneous values are subtracted. An averaging period of 30 minutes (denoted by the overbar) is used and is considered large enough for statistical confidence in the covariance quantity but is short enough to resolve the structure of the diurnal cycle. Wind vector measurements made at experimental sites that are not perfectly flat can result in non-zero vertical wind velocities measured from the "vertical " coordinate system of the measurement platform. At the end of an average period, vertical turbulent fluxes perpendicular to the mean horizontal wind (which generally follows the contour of the land surface) are obtained by mathematically rotating the coordinate system of the measurement frame of reference (sonic anemometer) to obtain a zero _ _ mean vertical and transverse velocity (w=v=0). Details of this procedure described by Wesely (1969) are outlined by Businger (1986) and Baldocchi et al., (1988). The three components of the wind vector are determined with a sonic anemometer ( R2, Gill Instruments, Hampshire, England). The stable long-term operational characteristics of this instrument and its ability to continue measurements during cold weather and light rain events (Yellard et al., 1994), as well as its low power consumption, were important considerations in the selection of this anemometer. The symmetric head design of the R2 with its slender support structure produces little flow distortion (Grelle and Lindroth, 1994) and is well suited for measurements in the the relatively flat and open locations of the Little Washita Watershed and Champaign, Illinois sites Fast response water vapor and CO2 concentration measurement are made with an open-path, fast response infrared gas analyzer (Auble and Meyers, 1992). This sensor was used extensively for flux measurements during recent ARM (Doran et al., 1992) and BOREAS (Baldocchi et al., 1997) experiments. In a recent evaluation of open and closed path sensors for water vapor and CO2 concentrations, Leuning and Judd (1996) found that for the measurement of CO2, this sensor displayed minimal cross sensitivity to water vapor (see Leuning and Moncrieff, 1990). 6.0 Data Format Standard meteorological data collected at each site. The following are the variables, in order as they appear in the file. jday Julian Day time LST, half hour ending w_speed propeller anemometer (10 meters, Bondville ISIS) w_dir wind direction (10 meters, Bondville ISIS) Ta air temperature (C), at 3 m RH relative humidity at 3 m Pres surface pressure in mb Rg incoming global radiation (W/m2) Par_in incoming visible radiation (0.4-0.7 um) in uE/m2/s Par_out outgoing or reflected visible light Rnet net radiation (W/m2) GHF soil or ground heat flux (W/m2) rain total rain for half hour (inches) wet wetness sensor (in voltage with higher values indicating wetness) IRT surface or skin temp (C) 2_cm soil temp at 2 cm (C) 4_cm soil tmep at 4 cm 8_cm soil temp at 8 cm 16_cm soil temp at 16 cm 32_cm soil temp at 32 cm 64_cm soil temp at 64 cm u_bar average wind vector speed (m/s) u'w' kinematic shear stress (m2/s2) u'2 streamwise velocity variance (m2/s2) v'2 crosswind velocity variance (m2/s2) w'2 vertical velocity variance (m2/s2) H sensible heat flux (W/m2) LE latent energy flux (W/m2) CO2 CO2 flux (mg CO2/m2/s) LW_in downwelling longwave from sky (W/m2) sm_5 soil volumetric water content at 5 cm zone (after November 19 1997) sm_20 soil volumetric water content at 20 cm zone (after November 19 1997) sm_60 soil volumetric water content at 60 cm zone (after November 19 1997) The eddy covariance sensors are located at 6 m AGL. The bulk density of the soil is 1.4 gm/cm3. The site is currently in corn stubble (like it would look after combining). I am currently working up more soils data, and will have that information available shortly. The standard meteorological sensors (Table 1) are sampled every 2 s with a datalogger and multiplexor (CR21x, Campbell Scientific, Inc.) and averages are computed every 30 minutes, coincident with the eddy covariance data. 7.0 Data Acquisition A laptop computer is configured in a mulitasking mode to simultaneously perform three operations. For the first and foremost task, measurements of the three componenets of the wind vector along with the speed of sound (from which the virtual temperature can be derived) are digitally sent from the sonic anemometer (which includes the digitized H2O and CO2 signals from the IRGA) to the laptop computer, which is housed in a small environmental enclosure. In the second task, the computer retrieves the standard meteorological data from the CR21X datalogger every 30 minutes and appends the data to an existing file. After midnight, the covariance data and standard meteorological data are copied to separate files with a name, year and calendar day header. The computer is equipped with a modem and cellular phone in order to retrieve the data and conduct occasional system checks. On average, data are retrieved from the laptop computers about once every two days. 8.0 Power Operation and Management To avoid the constraints of using standard line power, the entire flux/meteorological system is designed to operate on 12 volts DC making it truly remote and portable. The entire flux system, including all the instruments and data logging devices are powered by nine deep-cycle 12 volts DC batteries that are charged daily with solar panels (M75, Siemans, Inc.). Each solar panel is capable of producing 3 amperes at 12 volts in full sunlight. The batteries are enclosed in an insulated container that is 2/3 submerged into the ground near the base of the tower. Ten solar panels are required at the Illinois site while eight are used at the Little Washita location. Each charging system is controlled with a 30 ampere regulator. The regulator is equipped with a low voltage disconnect option that disconnects electronic devices with the largest power consumption when the battery voltage falls below 11.5 VDC. Table (2) lists the major instruments and corresponding power requirements. The entire system continuously draws about 3 amperes at 12 VDC. The 21X datalogger and cellular phone are connected directly to the batteries and operate continuously since they have low power demands. When the regulator disconnects the computer because of low voltage (i.e. long periods of cloudy weather), only standard meteorological data are logged. After the batteries are charged to 12.5 VDC, the computer, IRGA and sonic are reconnected and logging of the flux data resumes. As will be discussed later, this happens infrequently and only during the winter months when cloudy conditions persist during the relatively short daylight hours. 9.0 REFERENCES Auble, D. L, T. P. Meyers, 1992. An open path, fast response infrared absorption gas analyzer for H2O and CO2, Boundary-Layer Meteorology, 59, 243-256. Atlas, R., N. Wolfson and J. Terry, 1993. The effect of SST and soil moisture anomalies on GLA model simulations of the 1988 U.S. summer drought, J. of Climate, 2034-2048. Baldocchi, D. D. and T. P. Meyers, 1991. Trace gas exchange at the floor of a deciduous forest: I Evaporation and CO2 efflux, Journal of Geophysical Research, Atmospheres, 96, 7271-7285. Baldocchi, D. D., B. B. Hicks and T. P. Meyers, 1988: Measuring biosphere-atmosphere exchanges of biologically related gases with micrometeorological methods. Ecology 69:1331-1340. Chen. T. H., A. Henderson-Sellers, and A. J. Pitman, 1994. Recent progress in the Project for Intercomparison of Land Surface Parameterization Schemes (PLIPS), GEWEX News, 4, 8-9. Dolske, D. A. and D. F. Gatz, 1985. A field intercomparison of methods for the measurement of article and gas dry deposition, J. Geophysical Research, 90, 2076-2084. Doran, J. C., F. J. Barnes, R. L. Coulter, T. L. Crawford, D. D. Baldocchi, L Ballick, D. R. Cook, D. Cooper, R. J. Dobosy, W. A. Dugas, L. Fritschen, R. L. Hart, L Hipps, J. M. Hubbe, W. Gao, R. Hicks, R. R. Kirkham, K. E. Kunkel, T. J. Martin, T. P. Meyers, W. Porch, J. D. Shannon, W. J. Shaw, E. Swiatek, and C. D. Whiteman, 1992. The Boardman Regional Flux Experiment, Bulletin of the American Meteorological Society, 73, 1785-1795. Garratt, J. R., 1993. Sensitivity of climate simulations to land-surface and atmospheric boundary layer treatments - a review, J. of Climate, 6, 419-449. Grelle, A. and A. Lindroth, 1994. Flow distortion by a Solent Sonic anemometer: wind tunnel calibration and its assessment for flux measurements over forest and field, Journal of Atmospheric and Oceanic Technology, 11, 1529-1542. Henderson-Sellers, A., 1993. A factorial assessment of the sensitivity of the BATS land-surface parameterization scheme, J. of Climate, 6, 227-247. Henderson-Sellers, A. and R. E. Dickinson, 1992. Intercomparison of land surface parameterization launched, EOS, 73, 195-196. Jacquemin, B., J. Noilhan, 1990. Sensitivity study and validation of a land surface parameterization using the HAPEX-MOBILHY data set, Boundary-Layer Meteorology, 52, 93-134. Leuning, R. and J. Moncrieff, 1990. Eddy covariance CO2 flux measurements using openpath and closed-path CO2 analyzers-corrections for analyzer water vapor sensitivity and damping of fluctuations in air sampling tubes, Boundary-Layer Meteorology, 53, 63-76. Leuning, R. and M. J. Judd, 1996. The relative merits of open- and closed-path analyzers for the measurement of eddy fluxes, Global Change Biology, 2, 241-253. Meehl, G. A. and W, M. Washington, 1988. A comparison of soil-moisture sensitivity in two global climate models, J. Atmospheric Sciences, 45, 1476-1492. Meyers, T. P. and D. D. Baldocchi, 1993. Trace gas exchange at the floor of a deciduous forest: II O3 and SO2 deposition rates, Journal of Geophysical Research, Atmospheres,98,2519-2528. Meyers, T. P. and D. D. Baldocchi, 1988, A comparison of models for deriving dry deposition fluxes of O3 and SO2 to a forest canopy. Tellus 40B:270-284. Pan, H. L., and L. Mahrt, 1987. Interaction between soil hydrology and boundary-layer development, Boundary-Layer Meteorology, 38, 185-202. Sato, N., P. J. Sellers, D. A. Randall, E. K. Schneider,, J. Shukla, J. L. Kinter III, Y. T. Hou, and E. Albertazzi, 1989. Effects of implementing the simple biosphere model in a general circulation model, J. Atmospheric Science, 46, 2757-2782. Sellers, P. J., and J. L. Dorman, 1987. Testing the simple biosphere (SiB) using point micrometeorological and biophysical data, J. Climate Applied Meteorology, 26, 622-651. Sellers, P. J., Y. Mintz, Y. C. Sud, and A. Dalcher, 1986. A simple biosphere model (SiB) for use within general circulation models, J. Atmospheric Science, 43, 505-531. Troen, I., and L. Mahrt, 1986. A simple model of the atmospheric boundary layer; sensitivity to surface evaporation, Boundary-Layer Meteorology, 37, 129-148. Vogel, C. A., D. D. Baldocchi, A. K. Luhar, K. S. Rao, 1994. A comparison of a hierarchy of models for determining energy balance components over vegetation canopies (submitted). Yellard, M. J., P. K. Taylor, I. E. Consterdine, and M. H. Smith, 1994. The use of the inertial dissipation technique for shipboard wind stress determination, J. Oceanic and Atmospheric Technology, 11, 1093-1108. Zeller, K. F., 1993. Eddy diffusivities for sensible heat, ozone, and momentum from eddy correlation and gradient measurements, USDA Forest Service Research Paper RM-313. __________________________________________________________________________ Table 1. Meterological variables measured at NOAA Energy Flux Monitoring Sites along with model number and manufacturer of instrumentation used. __________________________________________________________________________ Meteorological Variable Manufacturerer model number Air Temperature and RH Vaisala 50Y Net Radiation Radiation and Energy Balance Systems (REBS) Q*7 Global Radiation LI-COR LI-200 SB Precipitation Texas Instrument Wetness ATDD - Soil Heat Flux REBS PAR LI-COR LI-190 SB Atmospheric Pressure Vaisala PTB101B Surface Temperature Everest 4000A Soil Temperature ATDD - Soil Moisture Vitel hydra __________________________________________________________________________