[A-CG39] 熱帯インド洋・太平洋におけるマルチスケール大気海洋相互作用

[ACG39-12] Ensemble-based Atmospheric Reanalysis using a Global Coupled Atmosphere-Ocean GCM

*小守 信正¹、榎本 剛^1,2、三好 建正^1,3、山崎 哲¹、吉田 聡^1,2、田口 文明^1,4 (1.国立研究開発法人海洋研究開発機構、2.京都大学防災研究所、3.理化学研究所計算科学研究機構、4.東京大学先端科学技術研究センター)

キーワード：アンサンブルデータ同化、大気再解析、大気海洋結合モデル

Ensemble-based atmospheric data assimilation systems are sometimes afflicted with an underestimation of the ensemble spread near the surface caused by the use of identical boundary condition for all ensemble members and the lack of atmosphere-ocean interaction. To enhance the capability of the local ensemble transform Kalman filter (LETKF) with the Atmospheric GCM for the Earth Simulator (AFES), a new system has been developed by replacing AFES with the Coupled atmosphere-ocean GCM for the Earth Simulator (CFES). Two months of a retrospective analysis-forecast cycle with the coupled system (CLERA-A) from 1 August 2008 has been completed successfully, assimilating atmospheric observational data (the NCEP PREPBUFR archived at the UCAR) every 6 hours to update the atmospheric variables, whereas the oceanic variables are subject to no direct data assimilation. Although SST in CLERA-A suffers from the common biases among many coupled GCMs, the ensemble spreads of air temperature and specific humidity in the lower troposphere are larger in CLERA-A than in ALERA2. Therefore, the replacement of AFES with CFES successfully contributes to mitigate an underestimation of the ensemble spread near the surface. In addition, the basin-scale structure of surface atmospheric variables over the tropical Pacific is reconstructed from the ensemble-based correlation in CLERA-A but not in ALERA2. This suggests the importance of using a coupled GCM rather than an atmospheric GCM even for atmospheric reanalysis with an ensemble-based data assimilation system.