Upper Ocean Mixing Processes and Circulation in the Arabian Sea during Monsoons using Remote sensing, Hydrographic observations and HYCOM simulations
Abstract
The upper ocean processes in the Arabian Sea play significant roles in determining Sea Surface Temperature (SST) and air-sea fluxes, which are vital for understanding the monsoon and climate variability. Due to paucity of observations, our understanding of the critical influences of SST and salinity on upper ocean processes and their impact on atmospheric convection at seasonal and longer time scales (e.g. monsoon activity) has been limited. Among the world oceanic regions, only the Arabian Sea cools during summer monsoon under the influence of air-sea interaction processes and oceanic advective processes as well. The northern Arabian Sea experiences a combination of enhanced evaporation and the reduction in the solar radiation from October to January resulting in significant decrease of SST up to ~25° C during boreal winter. The Arabian Sea experiences more evaporation than precipitation and is connected to the warm and highly saline waters of the Persian Gulf and Red Sea effecting the salinity of the upper layer and the formation of the barrier layer (BL) within the isothermal layer. The BL in turn controls vertical mixing, mixed layer depth and warm pool dynamics affecting the onset and potential strength of the monsoon. The Indian Ocean shows significant variability in the distribution of Sea Surface Salinity (SSS), especially in the Arabian Sea (AS) and Bay of Bengal (BoB) in association with seasonal climate variations. Also, high salinity waters from the Persian Gulf and Red Sea circulate at subsurface and intermediate depth ranges as high salinity water masses in the AS and BoB. In order to balance the salt and mass, there is a need for exchange between these northern basins. The dynamics of ocean salt distribution is quite complicated. On annual time scale, there is a considerable exchange of salt from one basin to the other. However, the pathways of these high salinity waters are speculated only through watermass analysis using the hydrographic data, and the limits of extent of high salinity waters from one basin to the other are not yet clearly delineated. Surface circulation in the AS is unique. Because of its response to the semi-annually reversing monsoon winds, the major wind driven currents also undergo seasonal variations and flow reversals. In the AS, in a broad sense, the circulation is anticyclonic (clockwise) during southwest monsoon and cyclonic (counter clockwise) during northeast monsoon, and exhibits significant meso-scale variability. Seychelles–Chagos thermocline ridge (SCTR) in the southwest tropical Indian Ocean also appears to play an important role in the regional climate and intraseasonal variability at the periods of Madden-Julian Oscillation (40-60 day). While the contribution of the AS is important to the global oceans salt and heat budgets, and global climatic impact is well known to the scientific community, quantified analyses of its physical dynamics are underrepresented in the literature. Understanding these interesting oceanographic phenomena would be challenging due to sparse in-situ observations. This study proposes to understand the upper ocean mixing processes and circulation in the Arabian Sea using the sea surface salinity data from the newly launched Soil Moisture Ocean Salinity (SMOS) and NASA Aquarius/SAC-D salinity missions, as well as the well-established Argo floats, and HYbrid Coordinate Ocean Model (HYCOM) simulations, in addition special cruises will be conducted during the Southwest and Northeast monsoons.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512591
Entities
People
- Bulusu Subrahmanyam
Organizations
- Office of Naval Research
- United States Navy
- University of South Carolina