Diurnal Variability of Regional Cloud and Clear-Sky Radiative Parameters Derived from GOES Data. Part II: November 1978 Cloud Distributions

Abstract

Regional (250 ? 250 km2) diurnal cloud variability is examined using mean hourly cloud amounts derived from November 1978 GOES-East visible and infrared data with a hybrid bispectral threshold technique. A wide variety of diurnal variations in cloud cover is presented. A morning maximum in low cloudiness is found over much of the eastern Pacific. Many regions in the western Atlantic have peak low-cloud cover near noon. Low clouds reach a maximum most often near noon over most of South America and in the morning over North America. Midlevel clouds are most frequent in the evening over oceans and in the early morning over land. High-cloud maxima are found mainly in the late afternoon over land and in the midafternoon over the oceans. An early morning minimum in high-cloud-top temperature is observed over marine areas. The amplitude of the semidiurnal component of cloudiness is generally much less than that of the diurnal component. The largest diurnal cloud variations occur over the southeastern Pacific where low clouds are dominant. On the average, mean cloud fraction varied by about 0.35 in this area with a maximum near sunrise. Over the Amazon Basin, the vertical distribution of cloud cover follows a pronounced diurnal cycle which shows maximum high-cloud cover occurring in the late afternoon. A large-scale diurnally modulated circulation feature between the Amazon and the adjacent oceans is suggested. High clouds occur most frequently over the southern Andes during the afternoon and are most common over the adjacent lowlands during the night, indicating the existence of a diurnally-dependent mountain-plains circulation.