A22A-04
Relationships of Entrainment Rate with Dynamical and Thermodynamic Properties in Shallow Convection
Tuesday, 15 December 2015: 11:05
3010 (Moscone West)
Chunsong Lu1, Yangang Liu2, Guang Jun Zhang3, Xianghua Wu1, Satoshi Endo4, Le Cao1, Yueqing Li5 and Xiaohao Guo1, (1)NUIST Nanjing University of Information Science and Technology, Nanjing, China, (2)Brookhaven Natl Lab, Upton, NY, United States, (3)University of California San Diego, La Jolla, CA, United States, (4)Brookhaven National Laboratory, Upton, NY, United States, (5)Institute of Plateau Meteorology, China Meteorological Administration, Chengdu, China
Abstract:
This work examines the relationships of entrainment rate to vertical velocity, buoyancy, turbulent dissipation rate by applying stepwise principal component regression to observational data from shallow cumulus clouds collected during the Routine AAF [Atmospheric Radiation Measurement (ARM) Aerial Facility] Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site near Lamont, Oklahoma. The cumulus clouds during the RACORO campaign simulated using a large eddy simulation (LES) model are also examined with the same approach. The analysis shows that combination of multiple variables can better represent entrainment rate in both the observations and LES than the single-variable fitting equations and the three commonly used parameterizations. A new parameterization is thus presented that relates entrainment rate to vertical velocity, buoyancy and dissipation rate; the effects of treating clouds as ensembles and humid shells surrounding cumulus clouds on the new parameterization are discussed. Physical mechanisms underlying the relationships of entrainment rate to vertical velocity, buoyancy and dissipation rate are also explored. Furthermore, the effects of relative humidity in the entrained dry air on the above relationships are discussed; a possible physical mechanism for the effects is explored.
