.|  Baltimore Ecosystem Study
Meteorological Research Projects

The BES Reference Meteorological Station at McDonogh School
  • Peter M. Groffman, Cary Institute of Ecosystem Studies
  • Dan Dillon, Cary Institute of Ecosystem Studies
  • Martin Schmidt, McDonogh School
  • Kenneth Belt, USDA Forest Service
  • Larry Band, University of North Carolina
Many of the BES studies, such as those on urban soils, vegetation, social factors affecting urban environment or the inverse, air quality, and wildlife either require or are best reported with a climatological reference to the conditions under which they were conducted. Other studies, such as those on hydrology and urban influences on below-canopy microclimate require reference meteorological data as input. To serve these needs, a reference meteorological 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 has been the focus of the majority of BES research to date. The reference station also provides data that will be used for educational purposes; this is currently being done by the McDonogh school that hosts the station.

The BES reference station is unusual in the large number of variables measured. They include all the variables 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 are measured.

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 also provides reference meteorological conditions for empirical modeling of differences in air temperature, humidity, and wind speed for different types of land uses and structures (different "patch" types) at the local scale.

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.

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.

Day.--Day of the year, Julian.
Hour.--Hour on which averages are centered, EST.
Day of Month.---
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 (DIR_SU).--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.
The reference station is also described in a paper by Heisler and others (2000). Data management and quality are further described in a document by Heisler dated February, 2001, "A Note on Quality Control/Quality Assurance for the BES Reference Meteorological Station at McDonogh School"

Heisler, G.M., P.M. Groffman, L. Band, K. Belt, V. Fabiyi, G.T. Fisher, R.H. Grant, and S. Grimmond. 2000. A reference meteorological station for urban long-term ecological research, Baltimore Ecosystem Study. In: Third Urban Environment Symposium. Davis, CA. 14-18 Aug 2000. American Meteorological Society. Boston. pp. 189-90.