The Roles of Latent Heating and Dust in the Structure and Variability of the Northern Martian Polar Vortex

The winter polar vortices on Mars are annular in their potential vorticity (PV) structure, a phenomenon identified in observations, reanalysis, and some numerical simulations. Some recent modeling studies have proposed that condensation of atmospheric carbon dioxide at the winter pole is a contributing factor to maintaining the annulus through the release of latent heat. Dust and topographic forcing are also known to be causes of internal and interannual variability in the polar vortices. However, coupling between these factors remains uncertain, and previous studies of their impact on vortex structure and variability have been largely limited to a single Martian global climate model (MGCM). Here, by further developing a new MGCM, we decompose the relative roles of latent heat, topography, and dust as drivers for the variability and structure of the northern Martian polar vortex. Additionally, we analyze a reanalysis data set, finding that there are significant differences in vortex morphology and variability according to the spacecraft instrument used for the data assimilation. In both model and reanalysis, high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex, cause the destruction of PV in the low-to-mid-altitudes (>0.1 hPa), and significantly reduce spatial and temporal vortex variability. Through our simulations, we find that the combination of dust and topography primarily drives the eddy activity throughout the Martian year, and that although latent heat release can produce an annular vortex, it has a relatively minor effect on vortex variability.