Estimation of the Cloud Modification Factor from Satellite and Ground Data at Thessaloniki, Greece
Clouds are one of the basic factors that influence Earth’s climate and energy balance. Depending on their type and position they can reflect the incoming solar radiation or absorb the infrared radiation that is emitted by Earth. Their role in the climatic changes can be studied if their characteristics and variations are known with high temporal and spatial resolution. In this study, the cloud modification factor (CMF) is studied for the city of Thessaloniki, based on ground and satellite data. Given the radiation measurements at the ground station of Thessaloniki and model calculated values under cloudless conditions, the ground-based values of CMF are estimated. These are compared with data from the Meteosat Second Generation (MSG) satellite, provided every 15 min and from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, on board the Terra and Aqua satellites which provides the data twice a day. The comparison covers the period of 2007–2010. The linear regression between the monthly values of MSG and ground CMF has a slope of 0.81, while MODIS data are in better agreement with the ground measurements (slope = 0.94). The higher differences between the MSG and ground data correspond to cases of broken or very thick clouds.
KeywordsSolar Zenith Angle Aqua Satellite Thick Cloud Cloud Optical Depth View Zenith Angle
The authors would like to thank NASA and EUMETSAT for providing the satellite data as well as the LibRadtran team (www.libradtran.org) for providing the model algorithm. Jean Verdebout (JRC, Ispra) is highly acknowledged for the original algorithm. This study was mainly conducted and funded by project “Hellenic Network of Solar Energy” (HNSE), funded by the General Secretariat for Research and Technology, Greek Ministry of Education, Lifelong Learning and Religious Affairs.