SOUSEI 150-year Coupled Atmosphere-Ocean Reanalysis

An atmosphere and ocean reanalysis for a period exceeding 150 years is conducted with a climate model used for global warming projection under the Coupled Model Intercomparison Project Phase 5. The coupled atmosphere and ocean model is constrained by surface pressure observations(ISPD ver. 3.2.8), sea surface temperature observations (COBE-SST2; Hirahara et al. 2014), and a gridded observational data of subsurface temperature and salinity observations (an update version of Ishii and Kimoto 2009) by using one derivation of ensemble Kalman filter (EnKF; Hunt et al. 2007), integrating from 1850 to 2011. In the reanalysis system, the model runs with perturbations of COBE-SST2 given as a part of inflation under the context of EnKF. The prediction experiment using initial conditions every year from 1920 to 2011 also performed for evaluating the quality of assimilation results. Although the model resolution is low: Atmospheric model truncated at wave number 42 and a 1-degree resolution adopted in the ocean model, the past climate is realistically reproduced in the assimilation run in term of upper atmospheric circulation, precipitation, surface temperature on land, and teleconnection related to El Nino and Southern Oscillation (ENSO). However, better predictions skills for ENSO and climate events on decadal time scales than those with a simple initialization are not confirmed yet. The reanalysis outputs provide us ample opportunities of obtaining further knowledge on the past climate variations and changes particularly before the International Geophysical Year. In addition to this, we utilize the assimilation products for improvement of dynamical predictions on seasonal-to-decadal time scales under a Japanese domestic science program, SOUSEI. Atmospheric and oceanic data rescue activities are also taken by several science projects in Japan, collaborating with SOUSEI. We are archiving surface pressure data measured at stations of the Japan Meteorological Agency, marine observations by ships on the voyage out, upper air wind observation, radio sonde observations possibly for the entire period of each station. Further improvement of the system is currently undertaken for improved long-term climate predictions.