Properties of a Martian local dust storm in Atlantis Chaos from OMEGA/MEX data

In this study we present the analysis of the dust properties of a local storm imaged in the Atlantis Chaos region on Mars by the OMEGA imaging spectrometer on March 2nd 2005. We use the radiative transfer model MITRA to study the dust properties at solar wavelengths between 0.5 {\mu}m and 2.5 {\mu}m and infer the connection between the local storm dynamics and the topography. We retrieve maps of effective grain radius (reff), optical depth at 9.3 {\mu}m ({\tau}9.3) and top altitude (ta) of the dust layer. Our results show that large particles (reff = 1.6 {\mu}m) are gathered in the centre of the storm (lat=33.5{\deg} S; lon=183.5 W{\deg}), where the optical depth is maximum ({\tau}9.3 > 7.0) and the top altitude exceeds 18 km. Outside the storm, we obtain {\tau}9.3 < 0.2, in agreement with the estimates derived from global climate models (GCM). We speculate that a low thermal inertia region at the western border of Atlantis Chaos is a possible source of the dust storm. Moreover, we find evidence that topography plays a role in confining the local storm in Atlantis Chaos. The vertical wind component from the GCM does not provide any hint for the triggering of dust lifting. On the other hand, the combination of the horizontal and vertical wind profiles suggests that the dust, once lifted, is pushed eastward and then downward and gets confined within the north-east ridge of Atlantis Chaos. (continues in article)