Study of MODIS Retrieved Data and their Impact on Weather Simulations

Some satellite observations, in particular for microwave channels, are available only over ocean, such as the Special Sensor Microwave/Imager, while the Moderate Resolution Imaging Spectrometer (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 MODIS data, their errors are studied using reliable observations from other instruments such as radiosondes and ground-based Global Positioning System (GPS).

The impact of assimilating MODIS retrieved total precipitable water on convective storms is assessed using the Weather Research and Forecast (WRF) model and its data assimilation system. On 1st and 2nd June 2004, strong winds and hail were reported in southern US. At NSSL/NOAA, the advanced research WRF (ARW) model predicted those convective systems poorly in the area. Although assimilation of MODIS retrieved data, either TPW or temperature and dew point, produces negative or positive increment over the data coverage region, the impact of data on this particular case study is marginal for a 30h simulation period. The error of MODIS data is comparable to those of model forecasts over land; therefore, their impact could be limited, while the improvement might be more visible for phenomena over ocean. The evaluation of the latter is undergoing.