Total Precipitable Water (TPW) is defined as the amount of liquid water that would be produced if all of the water vapor in an atmospheric column were condensed. It is a very useful parameter for forecasters to determine atmospheric stability and the probability of convection and severe weather. The Atmospheric Infrared Sounder (AIRS, on Aura) and the Infrared Atmospheric Sounding Interferometer (IASI, on METOP-A) provide the capability to retrieve water vapor profiles at high vertical resolution, as well as monitor seasonal and diurnal trends of water vapor on a global basis.

The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site is centrally located near Lamont, OK. Among other instrumentation, this site contains a Microwave Radiometer (MWR) and a ground-based GPS sensor. These instruments may be used to derive TPW. In addition to the central site, 4 other boundary facilities also contain MWR instruments, however, only the central facility has a GPS.

The purpose of this study is to compare the retrievals of TPW from satellite-based infrared sounding instruments (AIRS and IASI) from ground-based instruments such as the MWR and GPS. Results are presented that highlight both the seasonal and diurnal variability of TPW for monthly mean climatologies, and the ability of each satellite retrieval to capture this variability.