3.08 Study of MODIS Retrieved Total Precipitable Water Data and Their Impact on Severe Weather Simulations Shu-Hua Chen 1* , Aidong Chen 1 , Jennifer Haase 2 , Zhan Zhao 1 , and Francois Vandenberghe 3 1 Department of Land, Air, and Water Resources, University of California, Davis, CA 2 Department of Earth and Atmospheric Sciences, Purdue University, W. Lafayette, IN 3 National Center for Atmospheric Research, Boulder, CO 1. INTRODUCTION Terra, the spacecraft of the first NASA Earth Observing System mission, was launched in February 2000, and a companion satellite Aqua joined it in May 2002. Both satellites are equipped with Moderate Resolution Imaging Spectrometer (MODIS) instruments. Some satellite observations, in particular from microwave channels, are available only over ocean, while the MODIS data are available over land and ocean and their spatial resolution is considerably high (5 km for this study). However, the MODIS data are limited to cloud free regions or the areas above cloud tops. Here, to better understand the characteristics and quality of the MODIS retrieved total precipitable water (TPW), the data are compared with radiosondes and ground-based Global Positioning System (GPS) TPW. A code has been developed to assimilate MODIS TPW into the Weather Research and Forecast (WRF) model three-dimensional variational data assimilation (3DVAR) system. Because of its high resolution over both land and ocean, MODIS data might have a potential to make some impact on severe weather simulations and forecasts. This new capability is demonstrated on two cases. One is the severe thunderstorm that occurred during early June 2004 over the southern US and the other is Hurricane Isidore, 2002 over the ocean. 2. OBSERVATIONS COMPARISON Table 1 shows the comparison of 16 paired TPW data between MODIS near Infra-Red (nIR) and radiosonde from stations in Australia for 0000 UTC 6 and 8 January, 2003. Note that the MODIS nIR data from Australia are used because they are available around 0000 UTC (day time only for nIR) when radiosondes are launched worldwise. Ten out of sixteen pairs have the differences of TPW less than 3 mm (shaded in Table 1) which is a reasonable error. However, other six show large discrepancies between radiosondes and MODIS data. Figure 1 shows the comparison of TPW between MODIS and ground-based GPS at sites over the southeast US. Again, the results are of comparable high quality, with the exception of the site near Miami, MIA3. Table 1: MODIS near Infra-Red (nIR) TPW (right column; in mm) comparison with Australian radiosonde integrated TPW (left column; in mm) for 0000 UTC 6 and 8 January, 2003. The shaded boxes indicate the difference of TPW between MODIS nIR and radiosonde is less than 3 mm. *Corresponding author address: Shu-Hua Chen, Land, Air, and Water Resource, Davis, CA 95616.