Cloud convection

This page describes the cloud convection (aka wet convection) algorithms of GEOS-Chem.

Overview

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].

--Bob Y. 13:13, 19 February 2010 (EST)

Relaxed Arakawa-Schubert scheme

This is the convection scheme that GEOS-Chem uses with both GEOS-3 and GEOS-5 meteorology. The source code for this scheme is located in routine NFCLDMX in convection_mod.f.

Hack and Zhang-McFarlane schemes

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

GEOS-4

The source code for the convection scheme required for GEOS-4 meteorology is contained within the F90 module fvdas_convect_mod.f. The main driver is called FVDAS_CONVECT. This routine calls the following routines:

1. ARCONVTRAN: Prepares arrays for use by CONVTRAN
2. CONVTRAN: Main driver for deep convection (i.e. Zhang/McFarlane scheme)
3. HACK_CONV: Main driver for shallow convection (i.e. Hack scheme)

GISS

The source code for the convection scheme required for GISS/GCAP meteorology is contained within the F90 module gcap_convect_mod.f. The main driver is called GCAP_CONVECT. This routine calls the following routines:

1. ARCONVTRAN: Prepares arrays for use by CONVTRAN
2. CONVTRAN: Main driver for deep convection (i.e. Zhang/McFarlane scheme)

There is no equivalent routine to HACK_CONV for the GCAP meterology. Instead, ARCONVTRAN and CONVTRAN are called with entraining mass fluxes, and then again with non-entraining mass fluxes.

--Bob Y. 13:11, 19 February 2010 (EST)

Validation

See Bey et al [2001], Liu et al [2001], and Wu et al [2007].

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. Hack, J.J., Parameterization of moist convection in the National Center for Atmospheric Research Community Climate Model (CCM2), <u<J. Geophys. Res., 99, 5551–5568, 1994.
6. Jacob, D.J. H. Liu, C.Mari, and R.M. Yantosca, Harvard wet deposition scheme for GMI, Harvard University Atmospheric Chemistry Modeling Group, revised March 2000.
7. 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. PDF
8. Moorthi, S., and M. J. Suarez, Relaxed Arakawa-Schubert: A parameterization of moist convection for general circulation models, Mon. Weather Rev., 120, 978– 1002, 1992.
9. Wu, S., L.J. Mickley, D.J. Jacob, J.A. Logan, R.M. Yantosca, and D. Rind, Why are there large differences between models in global budgets of tropospheric ozone?, J. Geophys. Res., 112, D05302, doi:10.1029/2006JD007801, 2007. PDF
10. Zhang, G. J., and N. A. McFarlane, Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian Climate Centre general circulation model, Atmos. Ocean, 33(3), 407–446, 1995.

--Bob Y. 13:11, 19 February 2010 (EST)

Previous issues that are now resolved

Fixed minor issues in MERRA cloud convection routine

Jenny Fisher discovered two minor issues in the MERRA convection routine DO_MERRA_CONVECTION (in module convection_mod.f):

ND38 diagnostic issue in routine DO_MERRA_CONVECTION

This update was tested in the 1-month benchmark simulation v9-01-02j and approved on 16 Aug 2011.

Jenny Fisher wrote]:

The bug is in routine DO_MERRA_CONVECTION. When DIAG38 is first written (around line 2056 in my code, after the comment titled "(3.4) ND38 Diagnostic"), DIAG38 is formed by adding T0 (converted to appropriate units) to the diagnostic each level K. This is correct. However, the second time we add to DIAG38 (below the cloud base, around line 2245 in my code), we add T0_SUM to each level. From what we can tell, T0_SUM represents not the washout from each level but instead the total wet scavenging loss, summed over the entire column. So we are effectively double counting in these levels and adding way too much. [Helen Amos and I] think this should instead be adding WETLOSS.

The fix is below:

                  IF ( OPTIONS%USE_DIAG38 .and. F(K,IC) > 0d0 ) THEN
                     DIAG38(K,IC) = DIAG38(K,IC)
!------------------------------------------------------------------------------
! Prior to 8/16/11:
! Now use WETLOSS instead of T0_SUM in the ND38 diagnostic below the cloud
! base.  WETLOSS is the loss in this level, but T0_SUM is the loss summed
! over the entire column.  Using T0_SUM leads us to over-count the tracer
! scavenged out of the column. (jaf, hamos, bmy, 8/16/11)
!     &                            + ( T0_SUM * AREA_M2 / TCVV_DNS )
!------------------------------------------------------------------------------
     &                            + ( WETLOSS * AREA_M2 / TCVV_DNS )
                  ENDIF

--Bob Y. 16:48, 16 August 2011 (EDT)

Wrong IF tests used in routine DO_MERRA_CONVECTION

This update was tested in the 1-month benchmark simulation v9-01-02j and approved on 16 Aug 2011.

Routine DO_MERRA_CONVECTION was using tracer flags IDTHg2 and IDTHgP to determine whether routines ADD_Hg2_WD, ADD_HgP_WD, and ADD_Hg2_SNOWPACK should be called. However, IDTHg2 and IDTHgP aren't ever defined and were set to zero, so these routines were never called even when the correct mercury species were used.

The fix is to replace these two lines of code

   IF ( IS_Hg .and. IC == IDT%Hg2 ) THEN
   ...
   IF ( IS_Hg .and. IC == IDT%HgP ) THEN

with these:

   IF ( IS_Hg .and. IS_Hg2( IC ) ) THEN
   ...
   IF ( IS_Hg .and. IS_HgP( IC ) ) THEN

--Bob Y. 16:47, 16 August 2011 (EDT)