Statistics – Methodology
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p21f..04m&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #P21F-04
Statistics
Methodology
5409 Atmospheres: Structure And Dynamics, 5445 Meteorology (3346), 5462 Polar Regions, 5464 Remote Sensing
Scientific paper
The winter season, westerly circumpolar flow of the martian atmosphere, like that of the terrestrial stratosphere, is concentrated into a jet which lies near 60 degrees latitude. This jet is known as the polar vortex. Polar vortices are of interest because they act as a barrier, inhibiting energy transport and potentially preventing the mixing of aerosols and chemical species. Thus, they control the response of winter polar processes to climatic forcings, both short term and long term. We have used the Mars Global Surveyor Thermal Emission Spectrometer nadir-pointed data set to generate a gridded time series of vertically resolved temperatures, and from this time series we estimate the horizontal wind field using an adaption of the "balance winds" methodology suggested by Randel (1987, J. Atmos. Sci, 44). From the wind field we calculate Ertel potential vorticity (PV), which is a conserved quantity for adiabatic flow and therefore acts as a dynamical tracer for evaluating the extent of mixing into the winter polar region. Animations of these PV maps are an important tool for visualizing the polar vortex's behaviors. The Mars polar vortex in the northern winter of 2003 shows a variety of interesting structures and behaviors, some of which appear to be characteristic of the martian polar vortices, and some of which are unique to that year and season. Characteristic features of the martian polar vortex include: 1) Rossby number of order 1, and often exceeding 1 in northern winter, in the core of the circumpolar jet; 2) a local maximum in PV on the poleward flanks of the jet, giving the potential vorticity field an annular shape and suggesting the possibility of barotropic instability; 3) a well organized northern hemisphere polar vortex that persists past Ls 330 into early 2004, and which we expect acts as an effective barrier to mixing over time scales less than the PV conservation time scale of 10 days. One notable event unique to the 2003 northern winter is a major displacement of the polar vortex, greatest on December 15, 2003, which was associated with a concurrent increase in global dust opacity. The polar vortex returned to its normal symmetric configuration by December 27.
Banfield Don
Conrath Barney J.
Gierasch Peter J.
McConnochie Timothy H.
Smith Masson D.
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