Evaluation of Ocean Data Assimilation in CAS-ESM-C: Constraining the SST Field

Author:

Xiao Dong, Renping Lin, Jiang Zhu and Zeting Lu

International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Abstract:

A weakly coupled assimilation system, in which SST observations are assimilated into a coupled climate model (CAS-ESM-C) through an ensemble optimal interpolation scheme, was established. This system is a useful tool for historical climate simulation, showing substantial advantages, including maintaining the atmospheric feedback, and keeping the oceanic fields from drifting far away from the observation, among others. During the coupled model integration, the bias of both surface and subsurface oceanic fields in the analysis can be reduced compared to unassimilated fields. Based on 30 model years of output from the system, the climatology and interannual variability of the climate system were evaluated. The results showed that the system can reasonably reproduce the climatological global precipitation and SLP, but it still suffers from the double ITCZ problem. Besides, the ENSO footprint, which is revealed by ENSO-related surface air temperature, geopotential height and precipitation during El Ni？o evolution, is basically reproduced by the system. The system can also simulate the observed SST–rainfall relationships well on both interannual and intraseasonal timescales in the western North Pacific region, in which atmospheric feedback is crucial for climate simulation.

Keywords: 

ocean data assimilation, ensemble optimal interpolation, CAS-ESM-C, ENSO footprint, atmospheric feedback, air--sea interaction, western North Pacific      

Citation: 

Dong Xiao, Renping Lin, Jiang Zhu, et al., 2016: Evaluation of ocean data assimilation in CAS-ESM-C: Constraining the SST field. Adv. Atmos. Sci., in press, doi: 10.1007/s00376-016-5234-8.