The Temperature Control of Cloud Adiabatic Fraction and Coverage

Abstract

AbstractThe fraction of cloud water compared to its adiabatic value is defined as the adiabatic fraction, fad. The accuracy of cloud representation in climate models is highly sensitive to mixing rate, manifested in fad. Here, we present the first fad distribution of marine boundary layer clouds over global oceans, retrieved by satellite observations. The fad is shown to decrease exponentially with cloud base temperature (CBT) and cloud depth, in agreement with the increasing evaporation capacity of entrained warmer air. Cloud cover decreases with increasing CBT, but to a much lesser extent than fad. The dependence of fad on CBT has little dependence on relative humidity or precipitation. The relationship between CBT and fad highlights the importance of CBT as a core control factor on cloud evaporation. The simultaneous decrease in cloud water content and cover with increasing CBT can lead to positive cloud feedback, resulting in greater future climate warming.