Improvements in tropical precipitation and sea surface air temperature fields in a coupled atmosphere–ocean data assimilation system

A coupled atmosphere–ocean data assimilation system, the Meteorological Research Institute-Coupled Data Assimilation System Version 1 (MRI-CDA1), was developed based on general circulation model and separate atmosphere ocean analysis routines operated by Japan Agency (JMA). To implement assimilation, 6-hr cycles with in outer loop are adopted atmospheric whereas incremental updates 10-day assimilation. (reanalysis) experiment (CDA-Exp) is conducted using MRI-CDA1 along an uncoupled reanalysis (UCPL-Exp) which same component of forced prescribed sea surface temperature (SST) similarly to JMA reanalysis, JRA-55. Climatological precipitation variations air (SAT) better represented CDA-Exp than JRA-55, brought about modification physics represent climate states. In CDA-Exp, SST adjustment amplifies lead/lag correlations between subseasonal precipitation. The coupling generates associated tropical instability waves, SAT field responds variations. SST–precipitation SST–SAT relationships weather timescale also recovered although they hardly seen UCPL-Exp. weather-timescale consistent state, parameters respond through physics. This study suggests that benefits would be more evident if ability its interaction improved.