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Impact of the Seasonal Variation on the CALIOP Derived Parameters
We find a very strong difference in the mean CTH as a function of latitude between
the passive and active measurements, particularly for the tropical areas (see Figure 6).
This region plays an important role in the hydrological and radiation energy balance
(Forster et al., 2007) and the differences observed can influence our understanding of
potential feedback mechanisms. Earlier, we associated the maximum of the CTH with
the position of the ITCZ for September. From the annual observations of CALIOP, we
are able to further study this aspect and to analyze the interannual variability of the
CTH. Figure 9 shows the temporal evolution of the CTH distribution from June, 2006
to May, 2007.
The mean values of CTH are comparable for both the middle and the northern
polar latitudes. Large differences appear for both the tropical and the southern polar
latitudes. We discuss hereafter the causes of these differences that can have a consider-
able impact on the cloud climatology.
Figure 9. Monthly average of the mean cloud top height against the latitude. Only the highest cloud
structure retrieved from the operational algorithm applied on CALIOP measurements has been used
between June, 2006 and May, 2007.
Tropical Variability of the Mean CTH
As shown in Figure 9, the maximum of the CTH distribution moves from north to
south of the equator with the ITCZ between February and August. Figure 10 shows the
location of the ITCZ retrieved by Waliser et al. (1993) with the CTH distribution. We
note that the correspondence between the ITCZ location and the mean CTH retrieved
from CALIOP is very similar. This confirms that the maximum of the median value of
the CTH can be associated with the mean position of the ITCZ. The extreme positions
 
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