Comparison of O-B between FY-3A and NOAA-18 for Microwave Sounding Data

FY-3A, which was launched on the 27th of May 2008, is a Chinese polar-orbiting meteorological satellite. Of particular interest for NWP applications are the two microwave instruments: the Microwave Temperature Sounder (MWTS) and the Microwave Humidity Sounder (MWHS). Given a three-hour orbital difference, the FY-3A observations are complementary in temporal space to NOAA-18 data for data assimilation and forecast applications in NWP. In this study, the FY-3A MWHS and MWTS observations are compared with NOAA-18 AMSU-A and MWH observations during January 2010. Firstly the monthly mean bias and standard deviation of O-B are separately calculated for both FY-3A and NOAA-18 microwave instruments, where O represents the satellite observations, while B is the simulated brightness temperature by RTTOV93 model based on the NCEP (The National Centers for Environmental Prediction) Global Forecast System final gridded analysis datasets. A three-step quality control is firstly applied, including a range check, NEDT (Noise Equivalent Delta Temperature) check, and an O-B bi-weighting check. The monthly mean bias and standard deviation of O-B are secondly calculated. It is found that the monthly mean bias and standard deviation of O-B from FY-3A microwave observations is of good quality, and of similar magnitude to those of NOAA-18 microwave data. Finally, the bias and error variance needed for assimilation of FY-3A data in Chinese GRAPES (Global/Regional Assimilation and PrEdiction System) are calculated and documented.