Estimation of Improvement in Indian Summer Monsoon Circulation by Assimilation of Satellite Retrieved Temperature Profiles in WRF Model

This study estimates the improvement in the simulation of Indian summer monsoon (ISM) circulation in the weather research and forecasting (WRF) model by assimilating temperature profiles from atmospheric infrared sounder. Two experiments are carried out from 1st May to 1st October during 2003-2011. In the first experiment control (CTRL), National Centers for Environmental Prediction final analysis forcing is used; whereas the second one (WRFAIRS) is same as CTRL but temperature profiles are assimilated. The improvements in the simulation are quantified using different statistical scores. Overall, the assimilation has improved the spatial and temporal distribution of various fields associated with ISM. Some of the major improvements are 1) elimination of asymmetric (north-south) SLP bias; 2) larger error reduction in winds; 3) reduction in the temperature biases at boundary layer and midtroposphere; 4) improvement in the vertical wind shear; 5) reduction in the water vapor mixing ratio errors by 0.3-0.6 g · Kg-1; and 6) improved simulation of monsoon circulation indices. Further improvements are noticed in dynamic and thermodynamic fields over different convective regions. This study advocates that accurate representation of the thermal structure in WRF is crucial for the simulation of realistic monsoon circulation. It may further pave way for developing/improving convective parameterization schemes for the model.

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