Geophysical Fluid Dynamics

Geophysical Fluid Dynamics (GFD) is, in general, considered to be the branch of fluid dynamics concerned with naturally occurring flows such as lava flows, oceans, and planetary atmospheres, on Earth and other planets. In particular, the effects of stratification and Earth’s rotation need to be taken into account in the equations of motion when the interest is on the dynamics of the ocean and the atmosphere, which will be the focus of this talk. Classic examples of GFD flows are the Jet Stream and the weather system in general; the swirling vortices that fill the oceanic basins; and currents hugging the coastlines often being baroclinic unstable. A challenging aspect of GFD is the multiple scales associated with the flows of interest. For example, dense currents are an integral part of the large scale thermohaline circulation and their water properties are of global importance. Recent studies have highlighted how dense currents entrain ambient water while flowing over sills or through constrictions or during their descent over the continental slope. The turbulence and mixing occurring at very small scales affects the density of these dense currents and hence their water mass location in the open ocean water column. A correct parameterization of mixing processes in general circulation and climate models is then essential for a correct representation of the ocean circulation. Another example of multiple scales interactions is the influence of oceanic vortices on the large scale circulation. Recent work has focused on formulating robust parameterizations of eddies to represent the important dynamics of oceanic vortices in general circulation and climate models, which do not completely resolve all the dynamically relevant scales. A correct parameterization of subgrid processes in climate models requires an understanding of the underlying fluid dynamics and GFD will play a fundamental role in this societally relevant endeavor.