Assessment of Ocean-Atmosphere Interactions for the Boreal Summer Intraseasonal Oscillations in CMIP5 Models over the Indian Monsoon Region

Abstract

The boreal summer intraseasonal oscillations (BSISO) are the prominent features of South Asian summer monsoon and mainly governed by the internal atmospheric dynamics and air-sea interactions. The present study aims to understand and evaluate the relationship between the convection and the associated air-sea interactions during the BSISO over the Indian monsoon region. To accomplish this, the present study utilizes observations and the 22 general circulation model (GCM) simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Representation of Indian monsoon season rainfall, sea surface temperature (SST) and latent heat fluxes in CMIP5 models such as climatological and intraseasonal are assessed using Global Precipitation Climatology Project rainfall by Taylor diagram metric. Results suggest that the majority of CMIP5 models simulated the northward propagation of precipitation and zonal wind at 850 hPa. However, models bias of BSISO variance shows significant spatial heterogeneity over the regions of the Arabian Sea (AS), Sub-Continent of India (SCI) and Bay of Bengal (BoB). The CMIP5 model which shows large biases in the mean state is degrading the northward propagation of BSISO. The phase relationship of ocean (land) and atmospheric interactions are diagnosed with lead-lag regression analysis. On ISO timescales over north Indian Ocean (NIO) convection leads the turbulent fluxes and westerly winds by a week. However, the majority of the models shows large uncertainty to represent this prominent feature over AS and SCI. Further, improper representation of the lead-lag relationship of SST and precipitation on ISO scales over the AS, BoB, and NIO in the CMIP5 models are attributing for significant bias variances. The present study advocates that BSISO propagation in CMIP5 models is mainly attributing from the internal atmospheric dynamics and air-sea interactions. However, for the realistic amplitude simulation of BSISO, proper representation of air-sea feedback mechanisms is crucial in CMIP5 models. The present study further suggests that the oceanic feedback processes of the CMIP5 models need to be improved for the accurate prediction of the intraseasonal variations.