  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)
