ESRL Global Systems Division

GPS-Met Project's Water Vapor Data Now Used by NWS Weather Models

Tuesday, June 28, 2005 marks a major milestone for the Ground-Based GPS Meteorology project, established at the NOAA Forecast Systems Laboratory in 1994. For the first time, GPS integrated precipitable water vapor data (GPS-IPW) are being used by a National Weather Service operational weather model running at the NOAA National Centers for Environmental Prediction (NCEP). This model upgrade, the 13-km Rapid Update Cycle (RUC), helps produce much improved moisture information at finer horizontal resolutions. The RUC incorporates GPS-IPW data along with moisture data from the GOES satellites, weather balloons, and surface instruments. With each hourly cycle, the RUC model produces a more accurate picture of the atmospheric moisture pattern using the most recent GPS-IPW data.

The FSL GPS-Met project was established in response to the need for improved moisture observations to support weather forecasting, climate monitoring, and atmospheric research. As the source of clouds and precipitation, water vapor is one of the most important components of the Earth's atmosphere. Indeed, it plays a critical role in the global climate system. As the most plentiful greenhouse gas, water vapor absorbs and radiates energy from the sun, and affects the formation of clouds and aerosols and the chemistry of the lower atmosphere.

In collaboration with other NOAA laboratories and federal, state, and local agencies, FSL has demonstrated the usefulness of GPS-Met in observing water vapor, which is currently under-observed. Most upper-air moisture observations are made by weather balloons that are launched twice daily and are spaced ~250 miles apart. Satellites also provide some observations, but do not provide water vapor information under cloudy conditions. Other ground-based instruments are expensive, require frequent calibration, and may not work well under all weather conditions. Because GPS-Met provides IPW data every 30 minutes at over 300 sites in the United States in all weather conditions and at a very low cost, it is considered a valuable atmospheric observing system for the future. GPS-Met is also used in cross-checking the validity of other observing systems, important in assuring that the systems are operating as designed.

Contact information
Name: Seth Gutman
Tel: 303-497-7031