Aerosol effects on the inter‐cloud region of a small cumulus cloud field

In a recent paper, we used observations to show that the inter‐cloud “cloud‐free regime” (or “twilight zone”) is not free of clouds and comprises small fragments of clouds, hydrated aerosol, as well as incipient, hesitant, and decaying clouds. In this paper we characterize the properties of, and investigate the aerosol affect on, the twilight zone using high resolution large eddy simulations of clean and polluted shallow cumulus. We analyze the occurrence of these clouds with weak signature and show that cloud fields forming in polluted environments are characterized by a more rapid decrease in liquid water path with increasing distance from cloud than their cleaner counterparts, and that the inter‐cloud zone contains significantly fewer low liquid water path pockets. This reduction in liquid water content in the area considered cloud‐free in the polluted cases is countered by more aerosol uptake of water vapor.

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