  We extracted a Martian water-ice cloud climatology from OMEGA data covering 7
Martian years (MY 26-32). We derived two products, the Reversed Ice Cloud Index
(ICIR) and the Percentage of Cloudy Pixels (PCP), indicating the mean cloud
thickness and nebulosity over a regular grid (1{\deg} longitude x 1{\deg}
latitude x 1{\deg} Ls x 1 h Local Time). The ICIR has been shown to be a proxy
of the water-ice column derived from the Mars Climate Database. The PCP
confirms the location of the main cloud structures mapped with the ICIR, and
gives a more accurate image of the cloud cover. We observed a denser cloud
coverage over Hellas Planitia, Lunae Planum and over large volcanoes in the
aphelion belt. For the first time, thanks to the fact that Mars Express is not
in Sun-synchronous orbit, we can explore the cloud diurnal cycle at a given
season by combining 7 years of observations. However, because of the eccentric
orbit, the temporal coverage remains limited. Other limitations of the dataset
are its small size, the difficult distinction between ice clouds and frosts,
and the impact of surface albedo on data uncertainty. We could nevertheless
study the diurnal cloud life cycle by averaging the data over larger regions:
from specific topographic features (covering a few degrees in longitude and
latitude) up to large climatic bands (all longitudes). We found that in the
tropics around northern summer solstice, the diurnal thermal tide modulates the
abundance of clouds, which is reduced around noon. At northern midlatitudes,
clouds corresponding to the edge of the north polar hood are observed mainly in
the morning and around noon during northern winter (Ls=260-30{\deg}). Over
Chryse Planitia, low lying morning fogs dissipate earlier and earlier in the
afternoon during northern winter. Over Argyre, clouds are present over all
daytime during two periods, around Ls = 30 and 160{\deg}.
