Microphysics, radiation and surface processes in the Goddard Cumulus Ensemble (GCE) model

Abstract

The response of cloud systems to their environment is an important link in a chain of processes responsible for monsoons, frontal depression, El Nino-Southern Oscillation (ENSO) episodes and other climate variations (e.g., 30-60 day intra-seasonal oscillations). Numerical models of cloud properties provide essential insights into the interactions of clouds with each other, with their surroundings, and with land and ocean surfaces. Significant advances are currently being made in the modeling of rainfall and rain-related cloud processes, ranging in scales from the very small up to the simulation of an extensive population of raining cumulus clouds in a tropical- or midlatitude-storm environment. The Goddard Cumulus Ensemble (GCE) model is a multidimensional non-hydrostatic dynamic/microphysical cloud resolving model. It has been used to simulate many different mesoscale convective systems that occurred in various geographic locations. In this paper, recent GCE model improvements (microphysics, radiation and surface processes) will be described as well as their impact on the development of precipitation events from various geographic locations. The performance of these new physical processes will be examined by comparing the model results with observations. Specifically, the impact of different ice schemes (i.e., three-class ice scheme, four-class two-moment ice scheme) on precipitation processes are examined and compared. Spectral bin microphysics are used to investigate precipitation processes under clean and dirty environments. The coupled GCE-radiation model shows that the modulation of relative humidity by radiative processes is the main reason for the diurnal variation of precipitation in the tropics. The coupled GCE-land surface model is used to examine the impact of heterogeneous land surface characteristics (soil-vegetation) on precipitation processes. The effect of ocean flux algorithms (e.g., the TOGA COARE flux algorithm and a simple bulk aerodynamic method) on surface fluxes, environmental convective available potential energy (CAPE) and precipitation processes are compared. In addition, the coupled GCE-ocean mixed layer (OML) model is used to investigate the physical processes that affect the variation of sea surface temperature, mixed layer depth and salinity.