Arabian Sea mixed layer deepening during the monsoon : observations and dynamics
Citable URI
https://hdl.handle.net/1912/5666Location
Arabian SeaDOI
10.1575/1912/5666Keyword
Ocean-atmosphere interaction; MonsoonsAbstract
The unusual twice-yearly cycle of mixed layer deepening and cooling driven by the monsoon
is analyzed using a recently collected (1994-95) dataset of concurrent local air-sea
fluxes and upper ocean dynamics from the Arabian Sea. The winter northeast monsoon has
moderate wind forcing and a strongly destabilizing surface buoyancy flux, driven by large
radiative and latent heat losses at the sea surface. Convective entrainment is the primary
local mechanism driving the observed mixed layer cooling and deepening, although horizontal
advection of thermocline depth variations affect the depth which the mixed layer
attains. Modifications of a one-dimensional mixed layer model and heat balance show that
the primary nonlocal forcing of the upper ocean is the horizontal advection of temperature
gradients below the mixed layer base. The summer southwest monsoon has strong wind
stresses and a neutral to stabilizing surface buoyancy flux, limited by the extreme humidity
of the atmosphere, which suppresses both the radiative and latent heat losses at the surface.
Wind-driven shear instabilities at the base of the mixed layer, which entrain cooler
and fresher water primarily produces the observed mixed layer cooling and deepening.
Horizontal advection of cooler water within the mixed layer influences the local heat balance
at the mooring site. Ekman pumping velocities play only a small role in the upper
ocean evolution during both monsoon seasons.
Description
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1997
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Suggested Citation
Thesis: Fischer, Albert S., "Arabian Sea mixed layer deepening during the monsoon : observations and dynamics", 1997-09, DOI:10.1575/1912/5666, https://hdl.handle.net/1912/5666Related items
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