Entrainment Rate Estimation in Stratocumulus Clouds and Affecting Factors

Abstract:

The entrainment rate, Cloud Top Entrainment Instability (CTEI) and the extent of decoupling of stratocumulus are studied based on the stratocumulus data from the Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) field campaign in 2017 and 2018. The correlation between mass flux just below cloud top and height is affected by the CTEI parameter κ, because buoyancy reverse can cause entrained air to penetrate downward. In ACE-ENA, we find that the magnitude of κ is dominated by latent heat jump variable, which is also the reason why κ and entrainment rate are negatively correlated. In some past studies, κ was found to be not a good predictor of decoupling. In comparison with the results in another campaign (POST; Physics of Stratocumulus Top), we find that there is great uncertainty about which latent/sensible heat jump variables are dominant in determining the κ value; one reason why κ may not be a good predictor of decoupling is the uncertainty of the effect of decoupling on latent and sensible heat jump variables.