Impacts of Assimilation of Sounding Channel Refinement at 53 GHz on Forecasting

Fine spectrum refines conventional spectral sounding channels by increasing the spectral resolution to improve further the vertical resolution for accurate detection of atmospheric parameters. The 50- to 60-GHz absorption band is mainly used to sound the vertical distribution of atmospheric temperature in the troposphere and stratosphere, and 53 GHz is located in the weak oxygen absorption line. FengYun-3E (FY-3E) Microwave Temperature Sounder-III (MWTS-III) has two sounding channels added to this absorption band, and initially realized the refinement of the sampling channels. In this article, by establishing the assimilation operator for the radiance data of MWTS-III in China Meteorological Administration Global Assimilation Forecasting System (CMA-GFS) 4D-Var, and using the in-orbit observations from FY-3E MWTS-III, we investigate the impact of refining sounding channels at 53 GHz on numerical weather prediction (NWP). Results show that the temperature increment has the largest value and the widest influencing area near the peak weighting functions of channels, and the intensity and range of the temperature increment also change as the number of assimilated channels increases. An increment index can help quantify the impact of channel refinement on the forecast field. After single-cycle assimilation, the root mean square error (RMSE) of atmospheric parameters in the analysis field shows a decreasing trend. After continuous assimilation, the RMSE of geopotential height has a positive effect on short-term forecasts as the number of assimilated channels increases. It can be seen that channel refinement at 53 GHz positively impacts the performance of NWP.