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Baltimore Ecosystem Study Meteorology Overview
Gordon M. Heisler, USDA Forest Service, Northeastern Research Station
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Introduction
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Meterological sampling locations. Image: Gordon Heisler
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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 primary reference meteorological station (“Primary” on map) 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.
A second weather station (“AWS” on map) was installed in a forested site north of Baltimore in 2005. This station uses instruments from Convergence Technologies, Inc. and is part of that company’s Weatherbug© system. The station measures air temperature and humidity, wind speed and direction, rain, an index of light, and air pressure. Current conditions in real time are available online here [HERE] Archived data is available as a compressed file (787kb) [HERE]. This station is near the bottom of a north-facing slope, which will sometimes influence the observations, and effects from the forest edge about 100 m to the north will sometimes extend to the station location. Nevertheless, this station probably provides a close approximation of predevelopment conditions. The forest consists of mature, second-growth mixed hardwoods that approach 30 m in height.
Both the primary station and the AWS station provide data that are available for educational purposes. This has been extensively done by the McDonogh school that hosts the station on their property. AWS observations are available to all schools that are part of the Weatherbug/Achieve school weather station network, of which there are some 8000 across the country (www.weatherbugschools.com/).
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Primary Station Details
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The primary 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 or, since March 2004, 15-minute 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 are 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 (Heisler, et al. 2006a; Heisler, et al. 2006b).
The primary 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. The reference station is also described in a paper by Heisler and others (2000).
Variables measured by BES primary weather station
| Day.-- | Day of the year, Julian. |
| Hour.-- | Hour on which averages are centered, EST. |
| Month.-- | - |
| 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. |
Available Primary Station Data
A sample of the hourly data (April 26, 2000 to July 7, 2000) from the McDonogh station is available on the BES Internet server. The metadata for this meteorological data are in the ORS system (www.orsprivate.org/group/bes/); go to Data, ORS Data Server, and search for non-spatial data with keyword “air temperature.”). Only average values are included in this data set. Maximum and minimum values are available from the author on special request.
Complete sets of average data for the primary BES weather station for years 2000 through 2006 may be accessed as zipped Excel files for the individual years at [HERE]. Descriptions of these data are in McDmet23.zip located with the weather data. Additional information is given in “Notes” worksheets in each data file. Years 2005 and 2006 include calculations of potential evapotranspiration. Year 2005 also includes time series charts that illustrate methods used for quality control of the data.
Daily means and maximum and minimum values of Primary station data are also available from the ClimDB web site. A tutorial for ClimDB by Heisler, Fisher and Walsh (2003) is available. The BES ClimDB data for download also includes daily data for recent years from the National Weather Service sites at the Baltimore/Washington airport (BWI) and downtown Baltimore near the Inner Harbor (DMH).
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Individuals Participating in Meteorological Data Collection
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- Gordon M. Heisler, USDA Forest Service
- Jessica Quin, USDA Forest Service
- Ian Yesilonis, USDA Forest Service
- Dan Dillon, Institute of Ecosystem Studies
- Peter M. Groffman, Institute of Ecosystem Studies
- John Hom, USDA Forest Service
- Martin Schmidt, McDonogh School
- Gary T. Fisher, US Geological Survey
- Richard H. Grant, Purdue University
- Kenneth Belt, USDA Forest Service
- Sue Grimmond, Kings College, London, UK
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References (available on request from the author at gheisler@fs.fed.us)
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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.
Heisler, G.; Tao, B.; Walton, J.; Grant, R.; Pouyat, R.; Yesilonis, I.; Nowak, D.; Belt, K. 2006a. Land-cover influences on below-canopy temperatures in and near Baltimore, MD. In: 6th Urban Environment Conference; Atlanta, GA.
Heisler, G.; Walton, J.; Grimmond, S.; Pouyat, R.; Belt, K.; Nowak, D.; Yesilonis, I.; Hom, J. 2006b. Land-cover influences on air temperatures in and near Baltimore, MD. In: 6th International Conference on Urban Climate; Gothenburg, Sweden. 392-395.
Heisler, Gordon; Fisher, Gary: Walsh, Jonathan. 2003. Accessing and using National Long Term Ecological Research (LTER) climate and hydrology data. A tutorial in PDF format. Available from the BES web site.
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