Geosciences Dept. Seminar: Time dependent aerosol effect on warm convective clouds

Abstract:

The overall aerosol effect on clouds and in particular, its synergy with the environmental thermodynamic conditions poses one of the biggest challenges in our understanding of the climate system and its future trend. In this talk, I will examine the interactions between clouds and their environment, focusing on warm convective clouds. Warm convective clouds pose a particular challenge in climate research as they are responsible for the largest uncertainty in assessment of tropical cloud feedbacks, and their properties often cannot be obtained from space (due to resolution limitations).

In this study, we explore both the cloud and the cloud field scales, using single cloud and LES numerical simulations. We show how changes in cloud’s processes are manifested in the cloud field’s properties and vice versa. For a given thermodynamic conditions, an increase in aerosol concentration leads to a competition between processes that amplify clouds development versus those that suppress it. This competition dictates an optimal aerosol concentration for which key macrophysical properties (like total mass or rain) reach their maximal values. This optimal aerosol concentration depends on the thermodynamic conditions such that deeper clouds would have larger optimum.

The coupling between the clouds and the field’s thermodynamic conditions adds another layer of complexity. Under polluted conditions, that suppress rain formation, there is an increase the atmospheric instability with time, whereas, on the other hand, cloud and rain forming in clean conditions tend to stabilize the lower atmosphere. The time evolution and those competing processes in the cloud and in the field scales will be discussed.

Seminar Organizer: Prof. Eyal Haifetz