Recent variations of cloudiness over Russia from surface daytime observations amg

Changes of total and low cloud fraction and the occurrence of different cloud types over Russia were assessed. The analysis is based on visual observations from more than 1600meteorological stations. Differences between the 2001-2010 and 1991-2000 years were evaluated. In general, cloud fraction tends to increase during the last years. A major increase of total cloud fraction and a decrease of the number of days without clouds are revealed in spring and autumn mostly due to an increase of the occurrence of convective and non-precipitating stratiform clouds. In contrat, the occurrence of Nimbostratus clouds tends to decrease. In general, the ratio between the occurrence of Cumulonimbus and Nimbostratus clouds has increased for the period 2001-2010 relative to 1991-2000. Over particular regions, a decrease of total cloud fraction and an increase of the number of days without clouds are noted.