Near-global survey of cloud column susceptibilities using ISCCP data

A new parameter, cloud column susceptibility, is introduced to study the ae rosol indirect effect, which describes the aerosol indirect effect more dir ectly without assuming how cloud droplet size will respond to changes of dr oplet number concentration. Between the two approaches that used to retriev e cloud column susceptibilities, the one that makes no assumption of consta nt liquid water content leads to smaller, even negative cloud column suscep tibilities. This finding is consistent with results of model studies and ob servations from the 1998-1999 Indian Ocean Experiment (INDOEX) that suggest that cloud liquid water content may be reduced during aerosol-cloud intera ctions. The results of this survey suggest that using constant liquid water content in models may lead to significant overestimation of the aerosol in direct effect.