J13.3 (Invited Speaker) Aerosols role in the determination of minimum cloud depth for precipitation and its climate implications

Wednesday, 26 January 2011: 2:00 PM
605/610 (Washington State Convention Center)
Daniel Rosenfeld, Hebrew University, Jerusalem, Israel; and E. Freud

Theoretical considerations show that in an adiabatic cloud parcel a nearly linear relationship between the number concentration of activated aerosols into cloud drops, Na, and the cloud depth required for onset of warm rain, Dp, must exist for a given cloud base temperature, except for when giant CCN dominate the rain forming processes. In a companion presentation, titled "Resolving both mixing and number of activated CCN in deep convective clouds" by Freud and Rosenfeld, we show that the mixing process of the convective clouds is close to extreme inhomogeneous, which nearly preserves the cloud drop effective radius, Re, while diluting the drop concentrations. It follows that the height at which clouds reach Re that is sufficiently large for effecive warm rain processes is dependent mainly on Na. It also follows that the satellite retrieved relations between convective cloud top Re and temperature, T, can be used to assess Dp and hence aerosol impacts on cloud microstructure and on precipitation forming processes. This will be demonstrated with data from several field campaigns including the Amazon, Israel and India.

The value of Dp with respect to maximum cloud depth, Dmax, determines whether the cloud would precipitate at all. Obviously, when Dp > Dmax clouds do not precipitate significantly. Because cloud dynamics change drastically between precipitating an non precipitating clouds, this criterion is critical in the determination of cloud dynamics, from marine stratocumulus to deep tropical convective clouds. Even when Dp < Dmax in deep warm based convective clouds the value of Dp has major impacts on the precipitation forming processes and the vertical distribution of latent heating.

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