A Study of the 2012 American Extremely Drought and Precipitation using Satellite Data Assimilation

Using an advanced weather research and forecasting model (WRF-ARW) with GSI data assimilation, the differences between drought and precipitation happened during the second week of 2012 have been investigated. The year 2012 was an extremely hot year with large area suffered drought in the US. But during the July 08-14, the south part of the US have a lot of rainfall which are really different from the main drought area. The control experiment and the experiment with satellite data assimilation have been validated using observations and satellite retrievals. The results of WRF with satellite data assimilation have good quality in rainfall distribution, even better than TRMM's results. The model's results showed that drought area is always under the control of a high pressure system, and the precipitation area is always associated with the intersection of warm and cold air. A diagnostic analyze also has been taken to verify the analysis. The distribution of area with high value of CAPE which exceed 1000 J kg-1 have good agreement with the background wind field, pressure systems and the precipitation areas. The area in the north with high value of CIN which exceeded 200 J kg-1 will prohibits the convection from moving to the north. Analysis showed that the continuous high pressure system in the north and the intersection of warm and cold air in the south are the main reasons for the differences occurred during this time.