Cloud-resolving numerical studies of the diurnal cycle of convection 
over the ARM SGP site

Description

The diurnal cycle of continental convection impacts the radiation budget, the local hydrological cycle and surface temperatures. The representation of the convective diurnal cycle is one of the key challenges for the general circulation models (GCMs). GCMs have a known bias towards producing deep clouds and precipitation at noon instead of mid- to late- afternoon. Cloud Resolving Models (CRMs) with high enough resolution can reproduce the diurnal cycle with better accuracy and therefore can be used as a tool for improvement of the diurnal cycle representation by cumulus parameterizations. A set of cloud-resolving numerical simulations was done with WRF v. 3.5 using the Advanced Research WRF (ARW) core, which includes multiple physics options for radiation, land surface, planetary boundary layer, and microphysics. The simulations were run on a 200 km x 200 km domain, with a 500 m horizontal resolution and 50 layers. Two cases of continental summertime diurnal cycle were chosen from amongst the dates used by Zhang and Klein (2010), who carefully selected the diurnally developing convection based on numerous observations over the SGP site. The WRF simulation results are compared with GOES satellite images and qualitatively confirm that the WRF model produces reasonable evolution of the cloud top height during the studied events. The results of the CRM simulations are contrasted with the GISS Model E2 single column (SCM) runs initiated with the ARM continuous forcing, and then with semi-prognostic SCM runs forced by thermodynamic profiles for the CRM domain mean and for the mean over the CRM convective area. Contrasting the two spatially averaged CRM regions with the SCM simulations may help distinguish parameterization errors associated with triggering, entrainment, and the effects of sub-grid variability in the environmental state. Zhang, Yunyan, Stephen A. Klein, 2010: Mechanisms Affecting the Transition from Shallow to Deep Convection over Land: Inferences from Observations of the Diurnal Cycle Collected at the ARM Southern Great Plains Site. J. Atmos. Sci., 67, 2943–2959.