  We investigate the global seasonal variations of near-surface relative
humidity and relevant attributes, like temperature and water vapor volume
mixing ratio on Mars using calculations from modelled and measurement data. We
focus on 2 am local time snapshots to eliminate daily effects related to
differences in insolation, and to be able to compare calculations based on
modelling data from the LMDZ GCM with the observations of MGS TES. We study the
seasonal effects by examining four specific dates in the Martian year, the
northern spring equinox, summer solstice, autumn equinox and winter solstice.
We identify three specific zones, where the near-surface relative humidity
levels are systematically higher than in their vicinity regardless of season.
We find that these areas coincide with low thermal inertia features, which
control surface temperatures on the planet, and are most likely covered with
unconsolidated fine dust with grain sizes less than $\sim$ 40$\mu$m. By
comparing the data of relative humidity, temperature and water vapor volume
mixing ratio at two different heights (near-surface, $\sim$ 23 m above the
surface), we demonstrate that the thermal inertia could play an important role
in determining near-surface humidity levels. We also notice that during the
night the water vapor levels drop at $\sim$ 4 m above the surface. This,
together with the temperature and thermal inertia values, shows that water
vapor likely condenses in the near-surface atmosphere and on the ground during
the night at the three aforementioned regions. This condensation may be in the
form of brines, wettening of the fine grains or deliquescence. This study
specifies areas of interest on the surface of present day Mars for the proposed
condensation, which may be examined by in-situ measurements in the future.

Earth and Planetary Astrophysics