Synoptic Modeling in the Eastern Arabian Sea during the Southwest Monsoon Using Upwelling Feature Models

Abstract

AbstractHydrographic observations along the western coast of India during the southwest (SW) monsoon season reveal upwelling in the equatorward surface flow and downwelling below the thermocline with a weak poleward undercurrent. Observations made previously during the peak of the SW monsoon in boreal summer showed that upwelling temperatures are much cooler (<23°C) than compared to the available climatology data in this region. A feature modeling technique is used to describe the temperature distribution associated with the West India Coastal Current (WICC) upwelling. This kind of formulation captures the upwelling and downwelling associated with the WICC reasonably well, though it requires the specification of a few observed offshore and nearshore temperature profiles. The temperature–salinity relationship from the Levitus climatology data is further used to obtain a compatible salinity distribution for the feature model. The efficiency of this feature model is further validated via a dynamical model simulation: here, the temperature–salinity feature model profiles are objectively melded with the Levitus climatology to create the synoptic initial condition. The WICC’s local circulation and simulated upwelling temperatures are more realistic in the dynamical model simulation with the feature model than in a simulation that does not utilize the upwelling feature model. The advantage of the feature modeling technique used herein is that it provides additional or new information that the OGCMs or prognostic ocean models can adapt to improve the latter’s initial condition and for synoptic forecasting. Furthermore, the generalized formulation of the upwelling feature model developed here may be used in other regional coastal oceans as well.