Title

On the heat budget of the Arabian Sea

Date of Award

2003

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Arthur J. Mariano, Committee Chair

Abstract

This study analyzes the heat budget of the Arabian Sea using satellite-derived sea surface temperature (SST) from 1985--1995 and other data sets. To better understand air-sea interaction, canonical average monthly and seasonal fields representing the spatial and temporal structure of the various components of the heat balance of the Arabian Sea are constructed from 30 years of monthly atmospheric and oceanic data.The SST over the Arabian Sea is not uniform and continually evolves with time. Cooling occurs over most of the basin during November through January and May through July, with the greatest cooling in June and July. Warming occurs over most of the basin during the remainder of the year, with the greatest warming occurring in March and September. Results indicate that the sign of the net heat flux is strongly dependent on location and month. The effects of net heat flux and penetrative solar radiation strongly influence the change in SST during February and March, and are less important during August and September. Horizontal advection acts to cool the SST during the northeast monsoon (NEM) months. During the southwest monsoon (SWM), horizontal advection of surface waters warms the SST over approximately half of the basin while upwelled water advected from the Somali Current drastically cools the northern tip. The intermonsoon months generally reflect both a slight cooling and warming of the SST. However, the effects of horizontal surface advection depend strongly on the position of eddies, gyres, currents and temperature gradients. The central Arabian Sea during the SWM is the only area where the change in SST is balanced by the entrainment and turbulent diffusion at the base of the mixed layer. According to previous studies and what has been calculated in this study, it appears that the base SST is set by the heat flux but deviations from this base, the changes in SST, are driven by the processes of horizontal surface advection and entrainment at the base of the mixed layer as explained by the dominant terms of the heat budget equation.Agreement between the temporal change in SST and the right hand side of the heat budget equation (Equation 5.1) is surprising. Throughout the year, monthly results over half of the basin (56%) and seasonal results over most of the basin (69%) agree within 3 degrees. Considering that the SST changes between 8--12 degrees over the year, this means that our results explain from 62--75% of the change in SST over 56%--69% of the Arabian Sea. This study shows that there are two major processes that contribute to the discrepancy in the change in SST calculated according to the heat budget equation, and the change in SST derived from satellite observations. The first is the effect of the horizontal advection term. The position of the major eddies and currents during the SWM greatly affects the change in SST due to the large gradient in temperature from the cold upwelled waters along the Somali coast to the warm waters from the interior of the basin. The second major process is the effect of the thermocline. In areas of shallow mixed-layer depth, high insolation and wind speeds either less than 3 m/s or greater than 15 m/s, the bulk formulae parametrization of the surface heat fluxes is inappropriate.

Keywords

Physical Oceanography

Link to Full Text

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