Postdoctoral Scholar: Mahdi Ben Jelloul
Intrinsic Low Frequency Variability of the
Wind Driven Circulation
Ocean circulation time scales are years longer than those of atmospheric circulation. Studying the behavior of the more time dependent ocean circulation is crucial to understanding climate variability over long periods of time. I study the modes of variability of the wind-driven ocean circulation. A mode is characterized as a precise intrinsic frequency that does not depend on a time scale imposed by the atmosphere and associated patterns of pressure and velocity. These modes operate on a decadal time scale and their structure results from the interplay of slow-moving waves in the earth's oceans and atmosphere caused by the Earth's rotation known as Rossby waves, with the stationary circulation forced by the mean winds and the geometry of the ocean basin.
Abyssal Stratification and "Thermohaline"
The ocean is cooled at the poles and heated at the equator, which results in a meridional, mainly thermally forced, overturning circulation. This produces a strong southward moving current in the Atlantic called the Deep Western Boundary Current that is fed by the sinking of cold water in the Arctic. The upwelling circulation spans the ocean interior, and there is a need for an energy source to pull up the cold deep water to the surface as well as to establish the stratification. Although ocean mixing processes potentially offer multiple energy sources, scientists still debate the exact energy source.
The goal of my research is to derive how the abyssal stratification is maintained and to determine the associated circulations. There is a subtle interaction between a static component of the ocean (stratification) and a dynamical one (the circulation) while taking into consideration the role of deep polar water sources and the mixing. Variations of the thermohaline circulation might be responsible for climate variability, including abrupt climate change.