1 3 DOI 10.1007/s00382-015-2478-4 Clim Dyn Role of upper ocean processes in the seasonal SST evolution over tropical Indian Ocean in climate forecasting system Jasti S. Chowdary · Anant Parekh · Sayantani Ojha · C. Gnanaseelan Received: 30 May 2014 / Accepted: 10 January 2015 © Springer-Verlag Berlin Heidelberg 2015 MLT change is underestimated compared to observations. Over the southern TIO region, MLT tendency is dominated by HF and Hadv terms in both observations and models. Contribution of HF to the annual cycle of MLT tendency is underestimated in CFSv1 whereas it is overestimated in CFSv2. Contribution of Hadv to MLT change is underes- timated by about 50 % in CFSv1 and 10–20 % in CFSv2 over southern TIO. These errors in HF and Hadv are asso- ciated with biases in HF components and surface wind representation. Evolution of lead–lag relationship between HF and MLT/SST in both the observations and models sug- gest the importance of HF in SST evolution over the TIO region. Over all, CFSv2 produced better SST seasonal/ annual cycle in spite of having cold bias. This improvement in CFSv2 may be attributed to better cloud–aerosol–radia- tion physics, which reduces radiation biases. Updated land- surface, ocean and sea ice processes and ocean component may be responsible for improved circulation and annual cycle of ocean–atmospheric components (winds and ocean circulation). However, there is a requirement for improved parameterization of turbulent HF and radiation estimates in CFSv2 to reduce the cold SST bias. Keywords Seasonal cycle · Sea surface temperature · Tropical Indian Ocean · Surface heat flux · Coupled models 1 Introduction Climatically tropical Indian Ocean (TIO) sea surface tem- perature (SST) is important because of its influence on the Indian summer monsoon (ISM; e.g., Izumo et al. 2008; Annamalai 2010; Boschat et al. 2012), east African mon- soon (e.g., Behera et al. 2005) and Australian monsoon (Yoo et al. 2006; Taschetto et al. 2011., references therein). Abstract In this study role of upper ocean processes in the evolution of sea surface temperature (SST) seasonal variations over the tropical Indian Ocean (TIO) is investi- gated in climate forecast system version1 (CFSv1) and ver- sion2 (CFSv2). Analysis reveals that CFSv2 could capture seasonal evolution of SST, wind speed and mixed layer depth better than CFSv1 with some biases. Discrepancy in reproducing the evolution of seasonal SST in coupled mod- els leads to bias in the spatial and temporal distribution of precipitation. This has motivated to carry out mixed layer heat budget analysis in determining seasonal evolution of TIO SST. Spatial pattern of mixed layer heat budget from observations and models suggest that the processes respon- sible for SST tendency differ from region to region over the TIO. Further it is found that models underestimated SST tendency compared to the observations. Misrepresentation of advective processes and heat flux (HF) over the TIO is mainly responsible for the distortion of seasonal SST change in the coupled models. Sub-regional heat budget analysis reveals that CFSv1 is unable to reproduce the annual cycle of mixed layer temperature (MLT) tendency over the Arabian Sea, while CFSv2 captured the annual cycle of SST with systematic cold bias. Misrepresenta- tion of the annual cycles of net HF and horizontal advec- tion (Hadv) are accountable for the low rate of change of MLT during most of the year. Hadv during summer season is underestimated by 50 and 25 % respectively in CFSv1 and CFSv2. Further, CFSv1 fails to simulate MLT ten- dency due to improper evolution of HF annual cycle over the Bay of Bengal. Though annual cycle of HF in CFSv2 is well represented over the Bay of Bengal, its contribution to J. S. Chowdary · A. Parekh (*) · S. Ojha · C. Gnanaseelan Indian Institute of Tropical Meteorology, Pune 411008, India e-mail: anant@tropmet.res.in