Improving Entrainment Rate Parameterization
Submitter:
Liu, Yangang — Brookhaven National Laboratory
Area of research:
Cloud Processes
Journal Reference:
Science
Parameterization of entrainment rate is critical for improving representation of cloud- and convection-related processes in climate models; however, much remains unclear.
Impact
This work seeks to improve understanding and parameterization of entrainment rate by use of aircraft observations and large-eddy simulations of shallow cumulus clouds over the U.S. Department of Energy’s Atmospheric Radiation Measurement Climate Research Facility's Southern Great Plains site, collected during the Routine AAF CLOWD Optical Radiative Observations (RACORO) field campaign.
Summary
It is found that entrainment rate, in both observed and simulated clouds, exhibits similar negative correlations with updraft velocity, buoyancy, and turbulent dissipation rate. Based on these relationships, a hierarchy of new parameterizations is developed to consider all these variables one by one with the stepwise principal-component regression. Also explored are the physical mechanisms underlying the relationships between entrainment rate, vertical velocity, buoyancy, and turbulent dissipation rate.
