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T. H. McConnochie, B. J. Conrath, D. Banfield, P. J. Gierasch (Cornell University), M. D. Smith (NASA/GSFC)
The terrestrial polar vortex has been understood to be the dynamical controlling mechanism for ozone depletion in the polar stratosphere (e.g., Schoeberl and Hartmann, 1991, Science, 251) for more than a decade. More recently, the earth’s stratospheric annular modes, which are essentially a weakening/strengthening oscillation of the polar vortex jet, have been shown to be coupled to and possibly even a driving mechanism for, the tropospheric Arctic Oscillation (AO) / North Atlantic Oscillation (NAO) phenomenon (Baldwin and Dunkerton, 2001, Science, 294). The Martian polar vortex is important not only as an analog to the terrestrial vortex, but as a possible controlling factor in key Mars climate processes. For example, just as the terrestrial polar vortex chemically isolates the polar stratosphere, the Martian polar vortex may act as a barrier to the transport of dust and ice aerosols towards the winter pole, thus influencing the water cycle and affecting the composition of the seasonal polar cap.
We calculate Ertel potential vorticity from the horizontal wind field, which is derived using a method similar to the "balance winds" technique suggested by Randel (1987, J. Atmos. Sci, 44). We find that the zone of high potential vorticity (PV), which characterizes the northern hemisphere polar vortex, is, in the global-dust-storm year, displaced northwards and intensified in the early winter as compared to the same season of the preceding year. We also find that this high-PV zone is typically annular in shape for the northern hemisphere martian winter. This is in contrast to the terrestrial polar vortex, where PV normally increases monotonically towards the pole and the high-PV zone is never annular.
In addition to the Ertel potential vorticity, we calculate the principal components of the day-to-day variability of MGS-TES temperatures. We find that the northern hemisphere Mars polar vortex exhibits an annular mode that may be similar to the terrestrial annular modes.
Funding for this research was provided by NASA through the Mars Data Analysis Program.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.