Three-dimensional distribution of cloud types over the USA and surrounding areas observed by CloudSat

Abstract

The vertical and horizontal distributions of the cloud types across different seasons and over the contiguous USA and surrounding areas are studied. The study is performed by collecting two years (2007 and 2008) of data from the CloudSat 2B-CLDCLASS product that uses effective radar reflectivity factor Ze, the presence of precipitation and ancillary data such as surface topography and the model-predicted temperature profile to classify clouds into seven distinct types. Considerable seasonal variations of the horizontal distribution of the cloud-type fractions are observed in the study area among different seasons and for both daytime and night-time CloudSat observations. It was found that during spring and summer, deep convective (Dc) clouds are observed much more frequently during night-time than during daytime over both the land and ocean. For the studied area and during daytime, low clouds were more frequent (up to ~50%) over the land and less frequent over the ocean compared with night-time observations. Analysis of the vertical distribution of cloud layers reveals that the fraction of cloudy scenes with two or more distinct cloud layers is the highest (up to 30%) over the northwest corner of the USA and the southwest corner of Canada and the nearby oceans. The southwest corner of the USA and the nearby east Pacific Ocean appeared to have the lowest fraction (<0.05%) of cloudy scenes with two or more distinct cloud layers. Over the land, approximately 18% of the total cloudy scenes are classified as two-layer clouds, whereas over the ocean, two-layer clouds are less frequent and range from 13% to 17% with a stronger seasonal dependency. Only about 2-3% of the total cloudy scenes are classified as multilayer clouds, with three or more distinct layers over both the land and ocean. The vertical distribution of cloud-top heights over both the land and ocean shows two distinct peaks. Over the land, the lower peak, at around 2 km, is almost independent of season, whereas the higher peak is seasonally dependent and varies between ~8 km (during winter) and ~11 km (during summer). Over the ocean, the lower peak is also observed near 2 km (or less), whereas the higher peak ranges approximately from 11 km (during winter) to 12 km (during summer). © 2012 Copyright Taylor and Francis Group, LLC.