Measured Constraints on Cloud-Top Entrainment to Reduce Uncertainty of
Non-Precipitating Stratocumulus Shortwave Radiative Forcing in the
Southern Ocean
Abstract
Stratocumulus cloud-top entrainment has a significant effect on cloud
properties, but there are few observations quantifying its impact. Using
explicit 0D parcel model simulations, initialized with below-cloud
in-situ measurements, and validated with in-situ measurements of cloud
properties, the shortwave cloud radiative forcing (SWCF) was reduced by
up to 100 W m-2 by cloud-top entrainment in the
Southern Ocean. The impact of entrainment-corrected SWCF is between 2
and 20 times that of changes in the aerosol particle concentration or
updraft at cloud base. The variability in entrainment-corrected SWCF
accounts for up to 50 W m-2 uncertainty in estimating
cloud forcing. Measurements necessary for estimating the impact of
entrainment on cloud properties can be constrained from existing
airborne platforms and provide a first-order approximation for cloud
radiative properties of non-precipitating stratocumulus clouds. These
measurement-derived estimates of entrainment can be used to validate and
improve parameterizations of entrainment in Global Climate Models.