GPS satellites, though first developed to determine the location of a person or place, are also very useful for meteorological purposes. Using the GPS signal delay, atmospheric temperature and moisture profiles can be determined. Of particular interest to meteorologists is total column water vapor, which is the amount of water vapor contained in a column over a given area on Earth. GPS networks can estimate precipitable water to an accuracy of within 1-1.5 mm.

Water vapor is especially important during storm development and in determining the strength and duration of severe storms. By analyzing water vapor distributions in environments where severe weather is developing or occurring, new knowledge can be formed about severe weather that could aid in earlier detection and warnings of storms and of severe weather events such as lightning and flash floods. We will use GPS water vapor retrievals to improve understanding of moisture associated with severe weather, and to examine impacts on forecast accuracy, using the dense network of GPS sites located in the Southern Great Plains of the United States.

GPS total column water vapor measurements will also be helpful in improving and validating moisture retrievals from rawinsondes and from other satellites. Rawinsondes only take atmospheric measurements twice a day in select locations, whereas the GPS network is extremely dense in states such as Oklahoma, Kansas, and Texas, with each sensor taking measurements every half hour. This allows scientists to see more small-scale water vapor variations with GPS sensors than with rawinsondes alone. During severe weather events, GPS sensors can also improve upon GOES Sounder data by taking measurements in cloud-covered areas. In cloud-free areas, GOES Sounder and GPS data can be compared. The advanced knowledge of water vapor variations in the atmosphere derived from ground-based GPS sensors will contribute greatly to the improvement of monitoring and forecasting the evolution of the atmosphere in areas of severe convection.