Satellite Retrieving CCN(S) By Using Clouds As CCN Chambers

Abstract:

Cloud properties are determined by cloud condensation nuclei supersaturation spectrum [CCN(S)] and by cloud base updraft speed (Wb). Until now Wb could not be retrieved from space. CCN is crudely estimated from aerosol optical properties. This practice is fraught with problems, especially in the vicinity of clouds, where it is needed most. In very low aerosol concentrations, where a small absolute difference in CCN makes a big difference in cloud properties, the aerosol optical properties become almost useless. These obstacles have impeded satellite quantification of cloud-aerosol interactions and explain the large uncertainty that we still have in ascribing these effects to climate forcing. Here I show emerging breakthrough capabilities to retrieve from satellites measurements both CCN(S) and Wb. This makes it possible to use the clouds as CCN chambers, where S is set and the nucleated cloud drop concentrations are counted. Retrieving convective cloud base drop concentrations (Nd) and updraft speed (Wb) allows the calculation of S. Then Nd is in fact CCN(S). The prospects of satellite retrievals of both CCN(S) and Wb will allow disentangling the effects of CCN and updrafts on cloud microstructure and radiative effects.