GCE

The Goddard Cumulus Ensemble (GCE) model, a cloud resolving model (CRM), has been developed and improved at NASA Goddard Space Flight Center over the past two decades.  The development and main features of the GCE model were published in Tao and Simpson (1993) and Tao et al. (2003b).  A review of the applications of the GCE model to develop a better understanding of precipitation processes can be found in Simpson and Tao (1993) and Tao (2003).  The 3D version of the GCE model is typically run using 256 x 256 up to 1024 x 1024 horizontal grid points at 1-2 km resolution or better.  An MPI version of the GCE model was recently developed (Juang et al. 2006).  It is well documented and easy to modify and improve.  It is also flexible enough to run on many different platforms using any number of CPUs.           

A Kessler-type two-category liquid water (cloud water and rain) microphysical formulation is used with a choice of two three-class ice formulations (3ICE), namely that by Lin et al. (1983) and the Lin scheme modified to adopt slower graupel fall speeds as reported by Rutledge and Hobbs (1984).  The sedimentation of falling ice crystals was recently included in the GCE scheme based on Heymsfield and Donner (1990) and Heymsfield and Iaquinta (2000) and was discussed in detail in Hong et al. (2004).  An improved four-class, multiple-moment ice scheme (4ICE) has been developed and tested for several convective systems in different geographic locations (Ferrier 1994; Ferrier et al. 1995).  The 4ICE scheme requires only minimal tuning compared to the 3ICE schemes.  In addition to the 4ICE scheme, two detailed, spectral-bin models (Khain et al. 1999, 2000; Chen and Lamb 1999) have been implemented into the GCE model.  Atmospheric aerosols are described using number density size-distribution functions.  The explicit spectral-bin microphysics can be used to study cloud-aerosol interactions and nucleation scavenging of aerosols as well as the impact of different concentrations and size distributions of aerosol particles upon cloud formation.  Please see Appendix A for a more detailed description of the GCE model.  These new microphysical schemes require the multidimensional positive definite advection transport algorithm (MPDATA; Smolarkiewicz and Grabowski 1990) to avoid "decoupling" between mass and number concentration.  Solar and infrared radiative transfer processes (Chou and Suarez 1999; Chou et al. 1999). Subgrid-scale (turbulent) processes in the GCE model includes the effects of both dry and moist processes on the generation of subgrid-scale turbulent kinetic energy (Klemp and Wilhelmson 1978; Soong and Ogura 1980).

Image above: KWAJEX Q1 heating time series consisting of diagnostically-calculated and GCE-CRM simulated profiles for three different time series during 1999 IOP: (a) 7-12 August (5-day), (b) 18-21 August (3-day), and (c) 29 August - 12 September (15-day). Green and red contours indicate positive and negative apparent heating regions, respectively.