Cloud Object Analysis of CERES Aqua Observations of Tropical and Subtropical Cloud Regimes: Four-Year Climatology

摘要

Four distinct types of cloud objects-tropical deep convection, boundary layer cumulus, stratocumulus, and overcast stratus-were previously identified from CERES Tropical Rainfall Measuring Mission (TRMM) data. Six additional types of cloud objects-cirrus, cirrocumulus, cirrostratus, altocumulus, transitional altocumulus, and solid altocumulus-are identified from CERES Aqua satellite data in this study. The selection criteria for the 10 cloud object types are based on CERES footprint cloud fraction and cloud-top pressure, as well as cloud optical depth for the high-cloud types. The cloud object is a contiguous region of the earth with a single dominant cloud-system type. The data are analyzed according to cloud object types, sizes, regions, and associated environmental conditions. The frequency of occurrence and probability density functions (PDFs) of selected physical properties are produced for the July 2006-June 2010 period. It is found that deep convective and boundary layer types dominate the total population while the six new types other than cirrostratus do not contribute much in the tropics and subtropics. There are pronounced differences in the size spectrum between the types, with the largest ones being of deep convective type and with stratocumulus and overcast types over the ocean basins off west coasts. The summary PDFs of radiative and cloud physical properties differ greatly among the size categories. For boundary layer cloud types, the differences come primarily from the locations of cloud objects: for example, coasts versus open oceans. They can be explained by considerable variations in large-scale environmental conditions with cloud object size, which will be further qualified in future studies.