Height Dependent Entrainment Measurements Using Observations

Convective entrainment rate is one of the most important and sensitive parameters in climate models and has drastic effects on simulated cloud feedbacks and climate sensitivity. Entrainment rate varies with height, as shown in both CRM simulations and in situ observations. In this study, we estimate height-dependent entrainment (HDE) rate using satellite observations of convective cloud top height and carbon monoxide. CloudSat data are used to identify deep convection and cloud top heights. Aura Microwave Limb Sounder (MLS)/Tropospheric Emission Spectrometer (TES) carbon monoxide measurements are then collocated with CloudSat to obtain ambient carbon monoxide profile. A single plume model is applied to Atmospheric Infrared Sounder Advanced Microwave Sounding Unit (AIRS/AMSU) sounding data to produce a series of candidate profiles of HDE. These candidate HDEs are then weighted by the cloud and carbon monoxide observations in a Bayesian manner to produce the final estimate of HDE. To compare with prior studies and GCM simulations, the HDE profiles are further converted to equivalent height-independent entrainment rates, which are then sorted by different environmental conditions. We identify two modes of entrainment rates from our observations: deep convective entrainment rates of 5-10% km^-1 and cumulus congestus entrainment rates of 10-20% km^-1. Entrainment rates decrease with could top height and relationships against mid-tropospheric relative humidity, convective available potential energy and convective inhibition are also explored. Comparisons are also made to GEOS-5 using a relaxed Arakawa and Schubert convective mass flux scheme.