Weather Data

Data about weather conditions are essential for the use of both usual and inverted models of atmospheric dispersion. Fortunately, weather data from the United States and around the world are available because data are collected in real time, in standard formats, and integrated in a central location that is publicly available without any technical or administrative barriers (http://weather.noaa.gov/).

Automated weather stations located at civilian and military airports around the world produce minute-by-minute observations of wind direction, wind speed, temperature, dewpoint temperature, visibility, precipitation, cloud cover, and other variables. These stations transmit hourly weather observations to the National Weather Service, which then makes available for free download the previous 24 hours' data. In the United States, the weather stations are part of the Automated Surface Observation System (ASOS) (www.nws.noaa.gov/asos/ index.html), a joint effort between the National Weather Service, the Federal Aviation Administration, and the Department of Defense. The stations code data using a standard format called METAR (see Chapter 32). The Federal Meteorological Handbook No. 1 (Office of the Federal Coordinator for Meteorological Services and Supporting Research, 1995) explains the meaning of the codes, enabling one to write a parser to extract the data contained within. Approximately 1700 stations in the United States report data.

Given the importance to aviation of accurate data about current weather conditions, a human operator usually reviews and corrects the data. The National Weather Service also performs quality control functions on data they receive (as part of the ASOS program).

The ASOS data do not include measurements of atmospheric turbulence such as atmospheric stability class. However, they do contain measurements that you can use in combination with other measurements to compute a Turner stability class (see WebMET, 2002). Turner stability classes have direct mappings to the commonly used Pasquill stability classes. The RODS Laboratory has been downloading and storing METAR data since 2003, including computing and storing the atmospheric stability class in this manner. The RODS Laboratory makes these data available to organizations that conduct biosurveillance.

Relative humidity affects survivability of FMDV and other biological agents as they travel long distances in the atmosphere, and thus measurements of relative humidity of atmosphere are needed for modeling the spread of these agents. Fortunately, computing relative humidity from measurements of temperature and dewpoint temperature is straightforward, and both these temperature measurements exist in the ASOS data sets.

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