Origins of Coupled Model Biases in the Arabian Sea Climatological State

Abstract

AbstractThis study investigates biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean?atmosphere models. The focus is to understand the cause of the large biases in the depth of the 20°C isotherm that occur in many of them. Other prominent biases are the depth and temperature of Persian Gulf water (PGW) and the wintertime mixed-layer thickness (MLT) along the northern boundary.For models that lack a Persian Gulf (group 1), is determined by the wintertime MLT bias through the formation of an Arabian Sea high-salinity water mass (ASHSW) that is too deep. For models with a Persian Gulf (group 2), if > MLT (group 2B), PGW remains mostly trapped to the western boundary and, again, directly controls . If MLT (group 2A), PGW spreads into the NAS and impacts because > 20°C; nevertheless still influences indirectly through its impact on .The thick wintertime mixed layer is driven primarily by surface cooling during the fall. Nevertheless, variations in ?MLT among the models are more strongly linked to biases in the density stratification (jump) across the bottom of the mixed layer than to biases. The jump is in turn determined primarily by sea surface salinity biases (?SSS) advected into the NAS by the West India Coastal Current, and the source of ?SSS is the rainfall deficit associated with the models? weak summer monsoon. Ultimately, then, ?D20 is linked to this deficit.