[A-AS02] 気象の予測可能性から制御可能性へ

[AAS02-06] Observing system simulation experiment of hourly global coverage of satellite microwave radiances using NICAM-LETKF

*Rakesh Teja Konduru¹、Jianyu Liang¹、Takemasa Miyoshi¹ (1.Data Assimilation Research Team, RIKEN Center for Computational Science, Kobe, Hyogo, Japan)

キーワード：observation system simulation experiment, satellite data assimilation, tropical cyclones, weather forecasting, convective systems, microwave radiances

This study investigates the impact of high frequency, such as 3-hourly and 1-hourly satellite microwave radiances from a new satellite, in global atmospheric data assimilation. The applicability of new satellite observations in weather forecasting is traditionally assessed using observation system simulation experiments (OSSE). We designed an OSSE framework using the global NICAM-LETKF system at 56 km horizontal resolution to understand the impact of such a high-frequency satellite radiances data assimilation. In OSSE, we used the radiative transfer for TOVS (RTTOV) model as an observation operator to generate new synthetic AMSU-A microwave radiances from the unbiased nature simulation. A free run was conducted with the NICAM model and treated as the reference (Nature) for the OSSE experiments. With the NICAM-LETKF system, we conducted five experiments, without data assimilation (NoDA), with only conventional data assimilation but not satellite radiances (NoSat), 6-hourly (6H), 3-hourly (3H), and 1-hourly (1H) satellite clear-sky radiances assimilation. The results showed that satellite microwave radiances assimilation improved the forecast of air temperature and wind over the global ocean and tropics as compared to NoSat experiments. With the increase in the assimilation frequency of the satellite radiances, the air temperature and winds showed improvement in their representation over the ocean and land. Global root mean square error of air temperature and winds reduced by 25-30% in the 1H than 6H as compared to NoSat. Over the ocean, microwave radiances assimilation improved the typhoon eyewall wind intensities and its structure for 1H satellite radiances assimilation compared to 6H. These improvements in the wind intensities are prominent during the landfall stage of the typhoon. Forecasting landfall storms' strong winds is essential for disaster prevention and mitigation. We showed the potential use of high-frequency microwave radiances in improving the forecast of synoptic scale convective scale systems like typhoons.