Cloud convection

This page describes the cloud convection (aka wet convection) algorithms of GEOS-Chem. We also invite you to read our Wet deposition wiki page, which contains information about the algorithms used for scavenging of soluble tracers.

Grell-Freitas (GF) scheme

GEOS-Chem uses the Grell-Freitas (GF) convection scheme when being driven by GEOS-IT meteorology (for all dates) and GEOS-FP meteorology (for dates on or after 01 June 2020). The source code for this scheme is located in the DO_GF_CLOUD_CONVECTION routine in GeosCore/convection_mod.F90 (see GitHub source).

Relaxed Arakawa-Schubert (RAS) scheme

The Relaxed Arakawa-Schubert (RAS) convection scheme is used in GEOS-Chem when driven by GEOS-FP meteorology (for dates prior to 01 June 2020) and MERRA-2 meteorology (for all dates). The source code for this scheme is located in the DO_RAS_CLOUD_CONVECTION routine in GeosCore/convection_mod.F90 (see GitHub source).

From Section 2, paragraph 10 of Wu et al. [2007].

A major difference between the GEOS-3, GEOS-4, and GISS models is the treatment of wet convection. GEOS-3 [and now also GEOS-5, ed.] uses the Relaxed Arakawa-Schubert convection scheme (Moorthi and Suarez [1992]). GEOS-4 has separate treatments of deep and shallow convection following the schemes developed by Zhang and McFarlane [1995] and Hack [1994]. The convection scheme in the GISS GCM was described by Del Genio and Yao [1993]. Unlike the GEOS models, the GISS GCM allows for condensed water in the atmosphere (i.e., condensed water is not immediately precipitated), resulting in frequent nonprecipitating shallow convection. In the wet deposition scheme, we do not scavenge soluble species from shallow convective updrafts at altitudes lower than 700 hPa in the GISS-driven model, whereas we do in the GEOS-driven model (Liu et al. [2001]).

Updraft scavenging of soluble tracers (as applied to both the Relaxed Arakawa and Hack/Zhang-McFarlane schemes in GEOS-Chem) is described in Section 1 of Jacob et al. [2000] and in Section 2.3.1 of Liu et al. [2001].

For information about validation of the RAS convective scheme in GEOS-Chem, see Bey et al. [2001], Liu et al. [2001], and Wu et al. [2007].