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Baltimore Ecosystem Study BES Reference Weather Station
Gordon M. Heisler, USDA Forest Service, Northeastern Research Station
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Abstract
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The data are from the Baltimore Ecosystem Study (BES) reference meteorological station. As part of the LTER program, BES includes research on hydrology, vegetation, social factors affecting urban environment, climatology, air quality, and wildlife. The reference station was installed at the McDonogh School in Owings Mills, MD, within the 30-km-long Gwynns Falls Watershed in April 2000. The Gwynns Falls Watershed is the focus of the majority of BES research. The variables measured at the reference station include all those in LTER Climate Committee Standards for Level 3 Meteorology: air temperature and humidity, precipitation, wind speed and direction, total solar radiation, incoming photosynthetically active radiation (PAR), reflected PAR, atmospheric pressure, soil temperature at two depths, and volumetric soil moisture. Net all-wave radiation and soil heat flux are also measured. The reference station is in a relatively open location in a pasture field. For most variables, both hourly averages and maximum and minimum values were measured. Only average values are included in this data set. Maximum and minimum values are available from the author on special request.
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Purpose
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Various BES studies measure variables such as precipitation, soil and air temperatures, and soil moisture. The reference meteorological station provides a basis for comparison of these variables at a location not too dissimilar from the generally open sites of first-order weather stations and most cooperative weather stations that are the source of most archived weather data. Net all-wave radiation, air temperature, humidity, and wind speed will be used in modeling evapotranspiration. The station will also provide reference meteorological conditions for empirical modeling of differences in air temperature, humidity, and wind speed for different types of land uses and structures.
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Quality
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All variables are measured with the manufacturers' calibrations as the instruments were installed in April 2000. For the data described here, there are no known instrument problems.
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Methods of Dataset Generation
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A Campbell Scientific (CSI, Logan, Utah) CR23X data logger with 4 MB of memory records hourly values for all sensors. Most hourly values are averages of measurements at 5 s intervals. Access is currently by site visits for downloading to a laptop computer. The system is powered by a 65-W solar panel. Variables: Day--Day of the year, Julian. Hour--Hour on which averages are centered, EST. Month. Day of Month. Year. Air Temperature (REBSTAVG, C)--For research on urban influence on below-canopy temperatures, it is important to keep radiation errors on air temperature measurements to a reasonable minimum. Power aspiration of radiation shields of temperature sensors is generally essential to keep temperature measurements sufficiently accurate. The reference station uses a resistance temperature device (RTD) in a custom shield aspirated by a 12-volt fan. This system is from Radiation and Energy Balance Systems of Seattle, Washington (REBS). Humidity (RH_AVG, %)--A Vaisala capacitive humidity sensor (CSI model HMP45C) measures humidity in a nonaspirated radiation shield. Atmospheric pressure (P_mb, millibars)--Pressure is measured with a Vaisala PTB101B Barometer just once, on the hour. Values are not corrected to sea level. Precipitation (Rain_TOT, inches)--Rainfall is measured by a tipping bucket rain gage (model RG 400-8 from J&S Instruments, Springfield, OH). It is logged to provide 5-min totals for all 5-min periods with measurable rain, and also as hourly totals. Only hourly totals for the previous 60 minutes are included here. The 5-min data is available on special request from the author. Wind speed and direction--These are measured at 2 m with a CSI Wind Sentry system. The advertised threshold speed is 0.5 m s-1. Wind Sentry systems from CSI have shielded anemometer bearings rather than sealed bearings. Shielded bearings provide a lower starting threshold speed. Six variables characterize wind: mean wind speed (WSMPSavg, meters per sec), vector wind speed (WSMPSu, meters per sec), vector wind direction (DIR_DU, degrees), standard deviation of wind direction (DIR_SDU, degrees), maximum wind speed for the hour (WSMPSMAX, meters per sec), and standard deviation of wind speed (WSMPS_SD, meters per sec). Total solar irradiance (totswAVG, watts/square meter)--This is estimated with a LI-COR (Lincoln, NB) silicon pyranometer. This sensor has a response that varies as the spectrum of radiation changes with sky conditions. Accuracy is sufficient for most urban climate modeling. PAR--Upward- and downward-facing quantum sensors from LI-COR measure PAR (parupAVG, moles per sec per square meter) and reflected PAR (pardnAVG, moles per sec per square meter). The PAR-reflected irradiance sensor is at a height of 1.7 m over a grass surface that is kept reasonably lawn-like and, therefore, representative of much of the urban area. Net radiation (Cnet_AVG, watts per square meter)--This is measured with a REBS all-wave net radiometer at a height of 1.7 m over grass. Soil temperatures--Measured at depths of 2 cm (Sl_T2AVG, C) and 10 cm (SlT10AVG) by thermistors (CSI model 107). Soil volumetric moisture content (water, % of soil volume)--Measured with a water content reflectometer, CSI Model CS615 that is installed to average moisture from the surface to 20 cm depth. One value is recorded on each hour. Soil heat flux (Sl_HtAVG, watts per square meter)--A REBS heat flux plate at a depth of 2 cm measures the rate of soil heat storage.
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Additional Comments
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The reference station site is on a gentle ridge with higher elevations to the east and west, but sky view is unobstructed to within 9° or less of the horizon in all directions. The nearest first-order station is at the Baltimore Washington International airport (BWI) about 28.5 km to the south. A National Weather Service station (DMH, WBAN 93784) that measures precipitation, temperature, humidity, and air pressure is located about 19.5 km to the southeast, just outside the Gwynns Falls Watershed, in the City of Baltimore.
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