Using GPM Data for Cloud and Precipitation Analyses

Efforts at the Global Modeling and Assimilation Office (GMAO) are ongoing to assimilate GPM Microwave Imager (GMI) radiance measurements using a recently developed all-sky (clear, cloudy, and precipitation) methodology. Previous uses of microwave imager data either neglected measurements affected by clouds and precipitation in radiance space or assimilated retrieved rain rates using highly inflated error estimates to limit their impact.

The above slide shows that when considering these observations (left), the system is now able to adjust the amount of cloud water in the background, a short-term 6-hour forecast (center), towards the measured reality. The regions denoted in this adjustment, or analysis increment (right), show that, after assimilating GPM/GMI radiances, cloud water was added near the center of the storm where the background was deficient and removed in a number of regions where the background had excess cloud.

This is being done in a meteorologically-consistent manner by using the model microphysics to adjust not only the clouds but also the corresponding temperature and water vapor fields. In this way, the clouds are not only analyzed but also retained through the integration of the forecast model.

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