Using CloudSat observations to evaluate cloud top heights from convection parameterization

Abstract

How high convective clouds can go is of great importance to climate. Cloud ice and liquid water that detrain near
the top of convective cores are important for the formation of anvil clouds and thus impact cloud radiative forcing and the
Earth’s radiation budget. This study uses CloudSat observations to evaluate convective cloud top heights in the National
Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5). Results show that convective cloud top
heights in the tropics are much lower than observed by CloudSat, by more than 2 km on average. Temperature and moisture
anomalies from climatological means are composited for convective clouds of different heights for both observations and
model simulation. It is found that convective environment is warmer and moister, and the anomalies are larger for clouds of
higher tops. For a given convective cloud top height, the corresponding atmosphere in CAM5 is more convectively unstable
than what the CloudSat observations indicate, suggesting that there is too much entrainment into convective clouds in the
model.