Journal des sciences de la Terre et du changement climatique

Abstrait

Spatially Decomposed Low Cloud Amounts and Wavelet Analysis

Neila Zarrouk and Raouf Bennaceur

In this work we have used monthly data series of low cloud amounts (LCA) describing the repartition and evolution of these cloud amounts in space and time. Thus we have decomposed values of low cloud amounts into spherical harmonics. For each month we have decomposed in spherical harmonics the values of LCA varying in space. Limiting our development to the fourth spherical wave we have obtained 35 components for each month covering the period 01/1990-12/1992. Each correspondent spherical component describing monthly variations of LCA is then submitted to Morlet wavelet analysis. Generally we can notice that the most LCA are obtained for winter and spring. Indeed Sun angle, solar intensity and clouds are important controls of the weather. At the equinox the Sun passes directly overhead at solar noon at the equator. Although the noon solar Sun angle on the equinox is greater than that on the first day of winter, the first remains low inducing also high amounts of clouds.