This article presents a monitoring of the atmospheric dust in the south polar region during spring of martian year 27 .
Our goal is to contribute to identifying the regions where the dust concentration in the atmosphere shows specific temporal patterns , for instance high , variable , and on the rise due to lifting or transport mechanisms .
This identification is performed in relation with the seasonal ice regression .
Based on a phenomenological examination of the previous results , hypothesis regarding the origin of aerosol activity of the southern polar region are proposed .
This is of paramount importance since local dust storms generated in this region sometimes grow to global proportions .
The imaging spectrometer OMEGA on board Mars Express has acquired the most comprehensive set of observations to date in the near-infrared ( 0.93-5.1 microns ) of the southern high latitudes of Mars from mid-winter solstice ( Ls=110° , December 2004 ) to the end of the recession at Ls=320° ( November 2005 ) .
We use two complementary methods in order to retrieve the optical depth of the atmospheric dust at a reference wavelength of one micron .
The methods are independently operated for pixels showing mineral surfaces on the one hand and the seasonal cap on the other hand .
They are applied on a time series of OMEGA images acquired between L _ { S } =220° and L _ { S } =280° .
As a result the aerosol optical depth ( AOD ) is mapped and binned at a spatial resolution of 1.0°.pixel ^ { \text { -1 } } and with a mean period of AOD sampling ranging from less than two sols for latitudes higher than 80°S to approximately six sols at latitudes in the interval 65-75°S .
We then generate and interpret time series of orthographic mosaics depicting the spatio-temporal distribution of the seasonal mean values , the variance and the local time dependence of the AOD .
In particular we suspect that two mechanisms play a major role for lifting and transporting efficiently mineral particles and create dust events or storms : ( i ) nighttime katabatic winds at locations where a favourable combination of frozen terrains and topography exists ( ii ) large scale ( \approx 10-100 km ) daytime thermal circulations at the edge of the cap when the defrosting area is sufficiently narrow .
As regards to the source regions around the cap , the sector with the highest AOD values/variability/increase spans longitudes 180-300°E around L _ { S } \approx 250° .
Later ( L _ { S } \approx 267° ) the cryptic sector becomes the most productive while the longitude sector 300-60°E remain moderately dust-generative .
Our work calls for new simulations of the martian surface-atmosphere dynamics at mesoscales to reproduce the observations and confirm the interpretations .