UMD AOSC Seminar

Ertel Potential Vorticity as a Diagnostic for the Mars Polar Vortex

Dr. Tim McConnochie
University of Naryland, Astronomy
NASA Goddard Space Flight Center

Polar vortices dominate the dynamics of the winter mid- and polar latitudes in the martian atmosphere, just as they do in the terrestrial stratosphere. In fact, polar vortices seem to be a universal feature of planetary atmospheres – they’ve been observed on Venus (Taylor, 2002), Jupiter (Orton et al., 2002), Saturn (Fletcher et al., 2008), and Titan (Teanby et al., 2008). Potential vorticity is well established as the analysis quantity of choice for the terrestrial polar vortices. Our goal is to extend the potential vorticity approach to Mars.

We have mapped 3-dimensional potential vorticity fields, which we have derived from Mars Global Surveyor Thermal Emission Spectrometer (TES) temperature soundings, for three martian years at both poles. We find that the northern martian winter polar vortex, like its terrestrial counter part, is bounded by a region of very steep potential vorticity gradients and is surrounded by a “surf zone” (in the sense of McIntyre and Palmer (1983)) of low potential vorticity gradients and frequent Rossby wave breaking. This configuration suggests that the northern martian polar vortex presents the same kind of barrier to mixing that the terrestrial polar vortex does.

However, unlike their terrestrial counterparts, the martian polar vortices are observed to extend all of the way to the surface (Mars has no tropopause), where surface drag will tend to destroy the barrier to mixing. Furthermore, the southern martian winter polar vortex lacks a well organized vortex edge region. The martian polar vortices also appear to have some kind of relationship to the uniquely martian phenomenon in which the main atmospheric constituent (carbon dioxide) is supersaturated and condensing at the surface and in the atmosphere throughout polar winter – the equatorward boundary of the zone of atmospheric supersaturation is observed to closely follow the polar vortex edge. A final peculiarity of the martian polar vortices is that they exhibit a prominent potential vorticity gradient reversal that violates the barotropic instability criterion and yet appears to persist and remain stable throughout the winter.

November 5, 2009, Thurday

Seminar: 3:30-4:30pm

Computer and Space Sciences (CSS) Building, Auditorium (Room 2400)
Refreshment is served at 3:00pm in the adjoining Atrium

[Contact: Eugenia Kalnay]
[AOSC | Seminar | Directions | Parking]