Changes in the microphysical structure of convective clouds over the Amazon
Alexandre
Araújo
Costa, Yale University, alexandre.costa@yale.edu
(Presenting)
Steven
C
Sherwood, Yale University, steven.sherwood@yale.edu
Massive burning takes place every year over central Brazil and the Amazon basin, contributing a significant aerosol loading that may affect clouds and climate regionally or even globally. In this work, we show evidences that changes in the aerosol field may be influencing the microstructure of convective clouds from its early stages, during which the development of warm rain is inhibited due to the large number of aerosol particles forming droplets, to the mature cumulonimbus stage, in which the size of the ice particles at the top of such clouds apparently follows the same behavior, with a larger number of smaller particles appearing under polluted conditions. From the SMOCC-EMfiN!-LBA data set, it was shown that, in the polluted environment, at the freezing level the droplets grew only to about half of Rosenfeld's threshold of 28 um. If warm rain initiation is expected only several kilometers above the freezing level, it is probable that ice-phase processes already started. In fact, on late September, the warm rain height is on the order of 8 km, going down to about 6 km during the transition to wetter conditions. The influence of the aerosol concentration apparently propagates to the glaciated tops of cumulonimbi, as the 3.7 um reflectance decreases significantly from September/October/November to December/January/February over the Amazon.
Submetido por Alexandre Araújo Costa em 25-MAR-2004