Robert Houze — University of Washington
Jian Yuan — Nanjing University
Category
Cloud Properties
Description
Annual mean (2007) climatology of anvil clouds associated with (a) small separated MCSs (<12000 km^2, the smallest 25%), (b) large separated MCSs (>40000 km^2, the largest 25%), and (c) connected MCSs. The color indicates percentage of area covered by MCS anvil clouds for each 5°x5° grid.
Mesoscale convective systems (MCSs) are objectively identified from the combination of 3 A-Train satellite instruments: MODIS, AMSR-E, and CloudSat. Active MCSs consisting of rain cores and anvil clouds are further divided into two types: separated MCS (SMCS) and connected MCS (CMCS). Combining these three types of A-Train data allows us not only to identify MCSs but also to separate their non-raining anvils from their raining regions. By separating anvils from the raining regions of MCSs, we are able to have quantitative global maps of anvil coverage (see figure). These maps show anvil clouds associated with small SMCSs are often found over land areas including continents and large islands, but the total coverage is small with maxima (~0.6%) over Africa and South America. In contrast, anvil clouds from large SMCSs are favored over warm oceans, and they cover several times more area overall than do small SMCSs. Anvil clouds from CMCSs are also common over open ocean areas, with most of them occurring over the Indian Ocean, Bay of Bengal, South China Sea, and West Pacific warm pool.
CloudSat radar data are used to characterize the vertical and internal structures of anvil clouds. With the CloudSat data we find that anvil cloud profiles from MCSs are of two major types: light rain and non-raining profiles. The former consist of a deep-cloud mode and a multiple-layers mode with raining clouds below high-topped clouds. The latter are dominated by thinner high-topped clouds with elevated bases.
In addition to MCSs, we have determined the global pattern of non-MCS anvil clouds. The mapping of anvils accomplished in this study lays a foundation for calculations of radiative effects of these anvil clouds. Preliminary radiative heating calculations applied to the anvil clouds identified in this study, as expected, show net radiative warming in the upper troposphere over areas covered by anvil clouds. This warming is a combination of shortwave warming concentrated in the upper part of anvil clouds and longwave cooling in the upper portion of the anvil and some warming near cloud base. More comprehensive investigations of the radiative heating structure of tropical anvil clouds from both MCSs and non-MCSs are in progress and, when applied to the maps of anvil coverage, will show the global pattern of anvil-cloud radiative heating.
