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The Wintertime Water Mass Formation in the Northern Arabian Sea: A Model Study

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  • 1 Division of Ocean and Atmospheric Sciences, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan
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Abstract

Using a level 2 one-dimensional turbulent closure model, the evolution of the Arabian Sea High Salinity Water mass (ASHSW) has been studied. Model-derived heat fluxes, sea surface temperature (SST), and mixed layer depths (MLD) are found to be in reasonable agreement with the observations. Winter cooling is characterized by a net heat loss of 40 W m−2 from the ocean, while there is a mild heat loss in summer. Wind-driven turbulent mixing is considerably stronger than buoyancy forcing during the summer monsoon and explains the mechanism for governing deep MLD and cool SST. During winter, a large latent heat release by the ocean due to prevailing dry air from the north, together with reduced solar radiation and increased longwave radiation due to lower cloudiness, decreases the net heat flux considerably. Negative buoyancy flux plays a major role in the formation of ASHSW during winter, while kinetic energy-driven vertical mixing is relatively weaker than during the summer monsoon. A sensitivity test has confirmed that the humidity plays an important role in the heat budget of the northern Arabian Sea during winter.

Corresponding author address: T. G. Prasad, Division of Ocean and Atmospheric Sciences, Graduate School of Environmental Earth Science, Hokkaido University, N-10, W-5, Sapporo 060 0810, Japan. Email: tgprasad@ees.hokudai.ac.jp

Abstract

Using a level 2 one-dimensional turbulent closure model, the evolution of the Arabian Sea High Salinity Water mass (ASHSW) has been studied. Model-derived heat fluxes, sea surface temperature (SST), and mixed layer depths (MLD) are found to be in reasonable agreement with the observations. Winter cooling is characterized by a net heat loss of 40 W m−2 from the ocean, while there is a mild heat loss in summer. Wind-driven turbulent mixing is considerably stronger than buoyancy forcing during the summer monsoon and explains the mechanism for governing deep MLD and cool SST. During winter, a large latent heat release by the ocean due to prevailing dry air from the north, together with reduced solar radiation and increased longwave radiation due to lower cloudiness, decreases the net heat flux considerably. Negative buoyancy flux plays a major role in the formation of ASHSW during winter, while kinetic energy-driven vertical mixing is relatively weaker than during the summer monsoon. A sensitivity test has confirmed that the humidity plays an important role in the heat budget of the northern Arabian Sea during winter.

Corresponding author address: T. G. Prasad, Division of Ocean and Atmospheric Sciences, Graduate School of Environmental Earth Science, Hokkaido University, N-10, W-5, Sapporo 060 0810, Japan. Email: tgprasad@ees.hokudai.ac.jp

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