Summer Total Cloud Cover Weekly Variability over Europe: Sign of Aerosols’ Indirect Effect?
The Day of Week (DoW) variability of total cloud cover (TCC) and aerosol optical depth (AOD550) and its statistical significance over six European regions is investigated using 10 years of summertime satellite observations from TERRA and AQUA MODIS. In general, positive (higher values during midweek) weekly cycles in both AOD550 and TCC appear over Central Europe (CE), while a strong negative weekly cycle appears over the Iberian Peninsula and NE Europe (NEE). A very similar TCC and AOD550 weekly variability appears over CE, SW Europe (SWE) and NEE and a rather similar one over Central Mediterranean (CM). Possible scenarios that could explain the common weekly variability of aerosols and cloud cover through the aerosol indirect effects are discussed. An effort is made to verify our results and the proposed aerosol-cloud interaction scenarios with the use of independent satellite TCC data from the ISCCP and ground-based precipitation data from the ECA&D project.