Urban influence on cloud cover estimated from satellite data

Abstract Quantitative assessment of the influence of a big city on the cloud cover was made using time series of satellite measurements. Data from the advanced very high resolution radiometer (AVHRR) on board NOAA satellites received during 1993–1996 over the Central European part of Russia have been processed to derive statistics on spatial distribution of cloudiness for a territory of approximately 7000 km2 covering Moscow (55.7 N, 37.6 E) and adjacent areas. Two basic cloud cover characteristics were studied: the total fractional cloud cover and the frequency of occurrence of cloudless scenes (or the clear-sky frequency). Results of the study show that the urban effect is most pronounced during spring and summer periods when a considerable increase in the cloud amount over most of the built-up city area is observed. The winter period presents only a slight evidence of the urban-induced modification of the cloud amount spatial distribution pattern. The average clear-sky frequency in the centre of the city was found to be 5.4% lower than in the nearest suburbs. No well-defined seasonal variations of the urban–rural difference in the clear-sky frequency were detected.