The influence of horizontal temperature advection on the stratocumulus lifetime: an idealized LES study

Abstract:

Conventional wisdom from satellite observations shows that marine low-lying clouds are fewer and less persistent in warm advection than in cold advection conditions. However, more recent observations show that it is not always the case: an initially well-mixed stratocumulus deck can maintain overcast for as long as several tens of hours in warm advection conditions. In this study, we investigate the physical mechanisms of response of stratocumulus cloud lifetime to horizontal temperature advection. We use a large-eddy simulation (LES) model to analyze the cloud liquid water path (LWP) budget for a series of idealized stratocumulus cases with the underlying sea surface temperature decreasing and increasing over time. In cold advection conditions, the quick dissipation of stratocumulus clouds is found to be mainly caused by enhanced entrainment drying, consistent with the conventional knowledge. In warm advection, the stratocumulus is more decoupled from the sea surface, making moisture supply limited. However, the weaker entrainment caused by a stronger inversion along with stronger net cooling of the cloud layer leads to a longer cloud lifetime in warm advection. Moreover, large-scale ascent motions that typically accompany warm advection contribute to prolonging stratocumulus lifetime. Overall, this study suggests that, everything else being equal, a stratocumulus deck advected over colder water is more persistent than over warmer water.