JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

M (Multidisciplinary and Interdisciplinary) » M-GI General Geosciences, Information Geosciences & Simulations

[M-GI28] [EE] Data assimilation: A fundamental approach in geosciences

Mon. May 22, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Shin'ya Nakano(The Institute of Statistical Mathematics), Yosuke Fujii(Meteorological Research Institute, Japan Meteorological Agency), SHINICHI MIYAZAKI(Graduate School of Science, Kyoto University), Takemasa Miyoshi(RIKEN Advanced Institute for Computational Science)

[MGI28-P05] A Reanalysis Experiment using a Coupled Atmosphere-Ocean Data Assimilation System in JMA/MRI

*Yosuke Fujii1, Toshiyuki Ishibashi1, Tamaki Yasuda2, Yuhei Takaya1, Takeshi Iriguchi1, Nariaki Saito1, Yoshiaki Takeuchi1 (1.Meteorological Research Institute, Japan Meteorological Agency, 2.Japan Meteorological Agency)

Keywords: Coupled Data Assimilation , Reanalysis, Precipitation, Global Ocean Heat Budget

JMA/MRI have developed a coupled Data Assimilation (DA) system, MRI-CDA1, based on JMA’s operational systems. The system adopts so-called weakly-coupled data assimilation procedure in which a coupled atmosphere-ocean model simulates the time-evolutions of the atmosphere and ocean fields while separated analysis routines generate analysis increments of the atmosphere and the ocean for modification of the coupled model fields. MRI-CDA1 is composed of the global atmosphere DA system for numerical weather predictions, NAPEX, the global ocean DA system for seasonal predictions, MOVE-G2, and the coupled atmosphere-ocean model for seasonal predictions, JMA/MRI-CGCM2.

MRI-CDA1 is applied to a coupled reanalysis experiment for the period from November 2013 to December 2015. Comparison of the reanalysis result with Japanese 55-year Reanalysis (JRA-55) indicates that the overestimation of the sea surface latent heat flux found in JRA-55 disappears in the reanalysis of MRI-CDA1. Consequently, the coupled system improved the global ocean heat budget. MRI-CDA1 also effectively suppresses the excess rainfall in the tropics in JRA-55, particularly in the Intertropcal Convergence Zone (ITCZ) in the Pacific. Anomaly correlation coefficients of precipitation in MRI-CDA1 with observation-based datasets (CMAP and GPCP) have quite similar distributions with the distribution for JRA-55, but decreases in a few areas. Although the sea surface temperature field is well reproduced by MRI-CDA1, the equatorial Pacific thermocline is shallower and the Pacific Equatorial Undercurrent is weaker than those in an uncoupled ocean reanalysis generated by MOVE-G2. These differences are likely to stem from difference of the bulk formula of the wind stress fields which force the ocean model.