HR: 11:56h
AN: A22B-08 INVITED     [Abstracts]
TI: Aerosol Interactions With Deep Convective Clouds and Their Climate Impacts Through the Hydrological Cycle
AU: * Rosenfeld, D
EM: daniel.rosenfeld@huji.ac.il
AF: The Hebrew University, Earth Sciences, Jerusalem, 91904 Israel
AB: Convective maritime clouds typically have well developed warm rain that much of it precipitates before ever freezing, moderate updrafts, little supercooled water and relatively high glaciation temperature. In contrast, continental clouds have much less warm rain, stronger updrafts, deeper mixed phase zone and more than 10 times more lightning for the same rainfall amount. These differences have been attributed traditionally to the differences between land and sea surfaces and to the greater relative humidity over oceans. Recent evidence show that the enhanced small CCN aerosols over land contribute significantly to the "continental" nature of the clouds, whereas clouds developing in pristine air over land have much more "maritime" nature. These differences are associated with similarly profound differences in the latent heating profile, where the continental clouds deposit the released latent heat higher in the atmosphere. Furthermore, greater instability is consumed for the same rainfall amount in continental convection, requiring greater recovery time of the convection by the radiative cooling of the troposphere. Sensitivity studies have shown that regional and global circulation systems are quite sensitive to such changes. These pollution aerosols changes are less obvious over ocean, mainly because polluted clouds over ocean are "hygroscopically seeded" by sea salt aerosols that enhance the warm rain processes. In spite of the reduced effect, over ocean, recent satellite (MODIS) analyses of cloud properties and aerosols show that cloud cover and vertical development of the convective clouds are much larger for greater aerosol amounts. Such aerosol increased cloud cover and vertical height can be explained by the aerosol effect on slowing down the precipitation forming processes, and the dynamic feedbacks on the cloud development. We can see these effects over oceans and not over land because aerosols cannot be detected by satellite as accurately over land. However, over land, where most CCN are anthropogenic, these effects are likely even greater than over ocean. Therefore, it is probable that anthropogenic aerosols have been already profoundly impact the precipitation and through that the cloud cover, cloud vertical development, hydrological cycle and hence the global circulation. Realistic simulations of these effects with GCMs is a major challenge, because much of the underlying cloud physics is still missing in them.
DE: 1803 Anthropogenic effects
DE: 1854 Precipitation (3354)
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting