Extended Abstract (588K)13C.6
Precipitation variability and barrier-layer formation in the North Indian Ocean
Shalini Mohleji, Purdue University, West Lafayette, IN; and C. A. Clayson
The Southwest Monsoon, occurring from the months of June through September, greatly affects and alters the air-sea exchanges existing in the Indian Ocean. The monsoon changes the wind and precipitation patterns over both the Arabian Sea and the Bay of Bengal. The Arabian Sea experiences stronger southwesterly winds and drier periods interspersed with intense short-lived precipitation events. On the other hand, the Bay of Bengal encounters a decrease in winds but a much greater amount of precipitation during the monsoon season. As a result, these two areas undergo temperature and salinity variations in the ocean structure due to changes in the surface heat, moisture, and momentum fluxes. Freshwater lenses are one phenomenon that affects the salinity in the ocean structure. They are low-saline freshwater patches near the surface that are created by periods of heavy precipitation. The importance of salinity variability on the thermodynamics and dynamics of the upper ocean has gained an increased appreciation in the last few years due to another phenomenon called the barrier layer. Much of the interest was initiated by the recognition of the barrier layer feature in the tropical Pacific, which has more recently been identified from climatological data in the Indian Ocean. The barrier layer occurs when the isothermal layer is deeper than the isohaline layer. This is the stable salinity-stratified region at the bottom of the surface mixed layer and is perceived to be an inhibitor of entrainment cooling due to its stability.
This study investigates the variability in the creation of freshwater lenses and barrier layers due to monsoonal induced surface flux variabilities of heat, moisture, and momentum. The thickness of the boundary layers and its relation to freshwater lenses depend strongly on the surface fluxes of moisture and momentum. In addition, it focuses on the effects of these events to subsurface mixing. The effects on subsurface mixing involve a deeper look into whether produced barrier layers truly act as barriers to mixing and entrainment, or whether turbulent mixing still occurs even during the existence of barrier layers. Comparisons with results from the tropical western Pacific will also be shown, highlighting differences in surface fluxes and the resulting changes in barrier layer and freshwater lens formation. A second-moment turbulence closure-based 1-D mixed layer model will be utilized to study the ocean surface and subsurface responses. The turbulent mixing, salinity, and temperature profiles will be evaluated from model simulations as the model explicitly calculates turbulence properties in the water column. The model is forced with ECMWF and TRMM data from the monsoon season of May-September 2000.
Session 13C, Ocean Atmosphere Interaction II (Parallel with Sessions 13A, 13B, and 13D)
Thursday, 2 May 2002, 11:00 AM-12:30 PM
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