| Description |
Many studies have examined both the modeling and observational aspects of aerosol-cloud interactions. The effect of the surrounding environment on individual clouds makes it difficult to isolate the signal of invigoration or suppression by aerosols, particularly at larger spatial and temporal scales. This study uses observations from the Tropical Rainfall Measuring Mission (TRMM), CloudSat, and Aqua satellites to identify convective clouds systems in clean and dirty environments. The MODerate Resolution Imaging Spectroradiometer (MODIS) aerosol index is collocated with radar precipitation features (RPFs) from TRMM and congestus cloud features (CFs) from CloudSat. Congestus clouds are also defined using Visible and Infrared Scanner (VIRS) infrared brightness temperature and radar-detected surface rainfall from 14 years of TRMM data. Using these definitions, the regional and seasonal variations of the population of congestus are presented globally. General differences are found between the properties of congestus over land and over ocean, especially the shapes of congestus. Ocean congestus are more bell-shaped, while land congestus tend to have flatter sides and larger area above the freezing level. This population of congestus is then used to examine the characteristics of clouds occurring in clean and dirty environments in different parts of the world. The ERA-Interim, which is paired with RPFs and CFs, is used to examine the environment in which these clouds occur. Aerosols are found to have different effects on clouds in different parts of the world. In some regions, such as Africa, environmental differences could possibly explain "invigoration" that has been attributed to aerosol effects. In other regions, such as the Amazon, environmental differences between clean and dirty cloud features remain small, indicating that aerosols could be causing at least part of the observed differences in cloud properties. Differences in clean and dirty congestus are very small and are limited to differences in the profiles of maximum reflectivity. The signal of the aerosol indirect effect is so small that it is very difficult to detect confidently using these methods. The environment must be considered in any study of the aerosol indirect effect, as important environmental changes can occur as aerosols are introduced to an air mass. |
