The Martian Polar Vortices: Climatology and Variability During the MGS/TES Period

We use an atmospheric reanalysis dataset to characterize the climatology and variability of the Martian polar vortices, particularly in relation to their morphology. Reanalyses combine state-of the-art global climate models with observations to produce a best estimate of the atmospheric state throughout a historical period. They allow access to variables that are not directly observed, such as wind components and vorticity, dynamically balanced with observables such as temperature and dust optical depth. In this study, we use the Mars Analysis Correction Data Assimilation (MACDA) dataset from 1999 to 2004 (almost three complete Martian years), a period covered by observations of the Thermal Emission Spectrometer on board NASA's Mars Global Surveyor. Potential vorticity and vortex centric diagnostics (area, aspect ratio, centroid latitude and orientation) allow us to assess the 4D morphology of the northern and southern winter vortex, highlighting their low variability (at least when compared to the variability of the stratospheric polar vortices on the Earth), but also their characteristic annular shape. Despite showing low inter-annual variability in general, the northern Martian polar vortex seems particularly sensitive to the radiative and dynamical effects of regional dust storms. We have analyzed a transient episode of `increased polar warming`, which occurred in the northern polar region during the regional dust storm in late winter of Martian year 26. The shape and strength of the northern vortex have been severely affected during the evolution of this southern storm, although no vortex breaking has been observed in the reanalysis dataset during the winter seasons covered by MGS/TES observations. The current availability of observations from the Mars Climate Sounder on board Mars Reconnaissance Orbiter will allow to extend the reanalysis of the Martian atmosphere to at least seven Martian winters, with great advantage for the study of the impact of dust storms on the inter-annual variability of Martian polar vortex dynamics and transport.