Cloud Cover Statistics

Cloud height data has been collected for 4 years over the CONUS and one year globally using the multi-spectral infrared sensors GOESVAS and NOAA HIRS. The analysis technique distinguished partially transmissive cirrus from other cloud forms. Cirrus were commonly found from 13 to 40 of the time over the CONUS. Seasonal and diurnal variations were small over the CONUS. More significant seasonal variations were found over the oceans from the movement of the subtropical high pressure systems and cyclonic storms and fronts in high latitudes. One half of the cirrus was associated with radar echoes in the summer while the other half was not. In winter only 22 of the cirrus were associated with radar echoes because of the lack of echo activity. Cirrus were slightly more numerous in winter than in summer. One half of the cirrus detected over the CONUS in January also was associated with jet streams. In summer this reduced to 10 to 30 because of weaker upper air winds.