Variability of the Indian Ocean SST and its possible impact on summer western North Pacific anticyclone in the NCEP Climate Forecast System
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The NCEP Climate Forecast System version 2 (CFSv2) provides important source of information about the seasonal prediction of climate over the Indo-Pacific oceans. In this study, the authors provide a comprehensive assessment of the prediction of sea surface temperature (SST) in the tropical Indian Ocean (IO). They also investigate the impact of tropical IO SST on the summer anomalous anticyclonic circulation over the western North Pacific (WNPAC), focusing on the relative contributions of local SST and remote forcing of tropical IO SST to WNPAC variations. The CFSv2 captures the two most dominant modes of summer tropical IO SST: the IO basin warming (IOBW) mode and the IO dipole (IOD) mode, as well as their relationship with El Niño-Southern Oscillation (ENSO). However, it produces a cold SST bias in IO, which may be attributed to deeper-than-observed mixed layer and smaller-than-observed total downward heat flux in the tropical IO. It also overestimates the correlations of ENSO with IOBW and IOD, but underestimates the magnitude of IOD and summer IOBW. The CFSv2 captures the climate anomalies related to IOBW but not those related to IOD. It depicts the impact of summer IOBW on WNPAC via the equatorial Kelvin wave, which contributes to the maintenance of WNPAC in July and August. The WNPAC in June is mostly forced by local cold SST, which is better predicted by the CFSv2 compared to July and August. The mechanism for WNPAC maintenance may vary with lead time in the CFSv2.
KeywordsIndian Ocean Anticyclonic circulation over the western North Pacific NCEP Climate Forecast System
The authors thank the two anonymous reviewers for their constructive comments, which improve the overall quality of the paper. This study was jointly supported by the National Natural Science Foundation of China (Grant 41105061), the National Basic Research Program of China (Grant 2012CB417202), and the Basic Research and Operation Program of the Institute of Plateau Meteorology, CMA (Grant BROP201215, BROP201318), and the Sun Yat-sen University “985 Project” Phase 3. Xingwen Jiang, who was partially supported by US National Oceanic and Atmospheric Administration and China Meteorological Administration Bilateral Program, thanks NOAA’s Climate Prediction Center for hosting his visit while this study was conducted.
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