Assimilating FY-3A VASS data into Chinese 3Dvar assimilation system (Grapes 3Dvar)

On 27 May 2008, China has successfully launched the FY-3A meteorological satellite as a research and development (R&D) satellite, with 11 payloads mounted, and the three instruments among the 11 payloads are vertical atmospheric sounding instruments similar to ATOVS: MicroWave Temperature Sounder (MWTS), MicroWave Humidity Sounder and InfraRed Atmospheric Sounder, generally called Vertical Atmospheric Sounder System, i.e., VASS, which will help to improve NWP forecast skill. Chinese Meteorological Administration has developed a three dimension variational data assimilation system (Global/Regional Assimilation and Prediction System, shorten as Grapes 3Dvar), and with the ATOVS radiance data directly assimilated by RTTOV as observation operator. In this study some challenging research works related to assimilating the FY-3A VASS data into Chinese 3Dvar assimilation system Grapes 3Dvar are performed, such as generation of the RTTOV coefficients for FY-3A VASS three instruments, data quality control, channel selection and bias correction, etc. To investigate the effects of the FY-3A VASS data in NWP model, 2 sets of assimilation experiments conducted: one is single instrument data assimilation experiment and the other is combinatorial data assimilation experiments. The preliminary results indicate that: the forecast skills are improved greater after FY-3A VASS data assimilation than before, and the different instrument has different effects on NWP forecast; the microwave sounders have more contribution than infrared sounder; the combinatorial data assimilation experiments get more positive effect than single instrument data assimilation experiment; the positive impact on the South Hemisphere is more clear than on North Hemisphere.