Urban effects on low-level clouds around the Tokyo metropolitan area on clear summer days

The frequency distribution of low-level clouds was estimated around the Tokyo metropolitan area on summer days without regional-scale cloud cover using NOAA satellite images from 1200 to 1500 LST during an 11-year period. The urban area is determined by the NDVI obtained by the same satellite. The low-level cloud frequency is higher over this large urban area than over rural areas in the early afternoon, especially over the radially extending urban areas along major highways or railways from the metropolis. We can conclude that the frequency of the low-level clouds is enhanced over the urban area, since the cloud frequency is negatively well correlated with the NDVI and their peaks fit well within a shift of about 2 km. The frequency of low-level clouds, however, is quite low in the coastal zone, even in the urban area, because of sea breezes.