Cloud convection

Overview

From Wu et al, 2007:

A major difference between the GEOS-3, GEOS-4, and GISS models is the treatment of wet convection. GEOS-3 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]. The treatment of boundary layer turbulence is also different in GEOS and GISS. The mixing depth in GEOS is estimated from the bulk Richardson number with surface friction [Holtslag and Boville, 1993] and in the GISS GCM it is estimated on the basis of the vertical profile of turbulent kinetic energy [Canuto, 1994; Canuto et al., 2001]. In either case, GEOS-Chem assumes instantaneous vertical mixing from the surface through the mixing depth [Bey et al., 2001].

Relaxed Arakawa-Schubert scheme

This is the convection scheme that GEOS-Chem uses with both GEOS-3 and GEOS-5 meteorology.

Hack and Zhang-McFarlane schemes

This is the convection scheme that GEOS-Chem uses with both GEOS-4 and GCAP meteorology.

References

1. Allen, D.J, R.B. Rood, A.M. Thompson, and R.D. Hidson, Three dimensional ²²²Rn calculations using assimilated data and a convective mixing algorithm, J. Geophys. Res, 101, 6871-6881, 1986a.
2. Allen, D.J. et al, Transport induced interannual variability of carbon monoxide using a chemistry and transport model, 101, J. Geophys. Res, 28,655-28-670, 1986b.
3. Bey I., D. J. Jacob, R. M. Yantosca, J. A. Logan, B. Field, A. M. Fiore, Q. Li, H. Liu, L. J. Mickley, and M. Schultz, Global modeling of tropospheric chemistry with assimilated meteorology: Model description and evaluation, J. Geophys. Res., 106, 23,073-23,096, 2001. PDF
4. Del Genio, A. D., and M. Yao, Efficient cumulus parameterization for long-term climate studies: The GISS scheme, in The Representation of Cumulus Convection in Numerical Models, Meteorol. Monogr., 46, 181–184, 1993.
5. Liu, H., et al. (2001), Constraints from 210Pb and 7Be on wet deposition and transport in a global three-dimensional chemical tracer model driven by assimilated meteorological fields, J. Geophys. Res., 106, 12,109– 12,128.

--Bob Y. 11:09, 19 February 2010 (EST)