Difference between revisions of "MERRA implementation details"

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*LIGHTNING: Eliminate the shallow-cloud inhibititon trap for MERRA, as we already do for GEOS-5
 
*LIGHTNING: Eliminate the shallow-cloud inhibititon trap for MERRA, as we already do for GEOS-5
*GET_OTD_LIS_SCALE: Compute ANN_AVG_FLASHRATE for MERRA in the same way as for GEOS-5.<br>'''''(NOTE: We may have to rescale this in the future.)'''''
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*GET_OTD_LIS_SCALE: Compute <tt>ANN_AVG_FLASHRATE</tt> for MERRA in the same way as for GEOS-5.<br>'''''(NOTE: We may have to rescale this in the future.)'''''
 
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*Read RH from disk, in the same way as for GEOS-5.<br>'''''(NOTE: MERRA RH is a 6-hr instantaneous field; GEOS-5 RH is 6-hr average field.)'''''
 
*Read RH from disk, in the same way as for GEOS-5.<br>'''''(NOTE: MERRA RH is a 6-hr instantaneous field; GEOS-5 RH is 6-hr average field.)'''''
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*Rewrote #if block logic where met fields are read in from disk
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*Now calls routines from <tt>merra_cn_mod.f</tt>, <tt>merra_a1_mod.f</tt>, <tt>merra_a3_mod.f</tt>, <tt>merra_i6_mod.f</tt> to read in met data
 
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Revision as of 17:09, 19 August 2010

NOTE: Information subject to change!

On this page we list the necessary modifications to GEOS-Chem for MERRA compatibility.

Overview

The GMAO MERRA data product is a 30-year reanalysis done with the GEOS-5.2.0 assimilation system. Therefore, within GEOS-Chem we can (for the most part) treat MERRA in the same way as we do for the GEOS-5 meteorology.

However, in order to reduce the volume of data produced (and for other technical concerns), GMAO chose to reduce the vertical and/or horizontal resolution of some important MERRA data fields. Also, some MERRA data fields have different units than in the GEOS-5 product. Because of this, some additional special handling may be required within GEOS-Chem.

Key similarities to GEOS-5

The following aspects of MERRA are identical to the GEOS-5 operational data product.

  1. The MERRA high-resolution grid (0.5° x 0.666°) is identical to that of GEOS-5.
  2. The MERRAvertical grid (72 hybrid levels) is identical to that of GEOS-5.
  3. By and large, the same data fields that were in the GEOS-5 product are also contained in MERRA.

Key differences from GEOS-5

The following aspects of MERRA differ from the GEOS-5 operational data product:

  1. The MERRA temporal resolution differs from GEOS-5 as follows:
    • Surface data: hourly averages (MERRA) vs. 3-hour averages (GEOS-5)
    • 3-D data: 3-hour averages (MERRA) vs. 6-hour averages (GEOS-5)
  2. Differences in individual MERRA met fields:
    • Most of the releveant MERRA 3-D data for GEOS-Chem are only available at 1° x 1.25° horizontal resolution.
    • OMEGA, PV, RH are 6-hr instantaneous data in MERRA but are 6-hr averaged data in GEOS-5
    • SNOMAS (snow mass) has units of kg/m2 in MERRA but mm in GEOS-5
    • Many of the precipitation fields (e.g. DQIDTMST, DQVDTMST, DQLDTMST, etc.) are saved on a 1.25° x 1.25° x 42 pressure levels instead of 72 hybrid levels. P -> hybrid interpolation is necessary.
    • The MERRA fields FRLAKE, FRLAND, FRLANDIC, FROCEAN, PHIS are time-invariant.

Required coding changes in GEOS-Chem

As noted in the section above, the similarities between GEOS-5 and MERRA (especially of the vertical grids) means that in most cases we can just treat MERRA in the same way as for GEOS-5. In many areas of the code, the coding changes are straightforward and simply involve an extension of C-preprocessor statements such as:

#if defined( GEOS_5 )

to

#if defined( GEOS_5 ) || defined( MERRA ) 

In other areas of GEOS-Chem the changes are more involved. Below we provide a description of the areas of GEOS-Chem that were modified for MERRA:

Headers directory

The following modifications for MERRA were made in the Headers/ directory:

File Modifications made
define.h
  • Add a new C-preprocessor switch named "MERRA".
CMN_SIZE
  • Added size parameters for MERRA 4 x 5 and MERRA 2 x 2.5 grids.

GeosUtil directory

The following modifications for MERRA were made in the GeosUtil/ directory:

File Modifications made
bpch2_mod.f
  • GET_MODELNAME: Add "MERRA_47L" and "MERRA" modelnames to the #if block
  • GET_NAME_EXT: Return grid name "geos5" for MERRA fields
directory_mod.f
  • Added MERRA_DIR variable for MERRA met fields
pressure_mod.f
  • GET_PRESSURE: Compute PEDGE for MERRA in the same way as for GEOS-5
  • INIT_PRESSURE: Initialize Ap and Bp for MERRA in the same way as for GEOS-5
time_mod.f
  • Add variable CT_A1
  • Add routines SET_CT_A1 and GET_CT_A1
transfer_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )

GeosCore directory

The following modifications for MERRA were made in the GeosCore/ directory:

File Modifications made
acetone_mod.f
  • OCEAN_SOURCE_ACET: Compute the ocean source of acetone for MERRA in the same way as for GEOS-5.
    (NOTE: We may need to eventually rescale this.)
convection_mod.f
  • DO_CONVECTION: Call the same convection routine (NFCLDMX) for MERRA as is done for GEOS-5
dao_mod.f
  • Add the following allocatable arrays for MERRA: DQRCU, DQRLSAN, FRSEAICE, FRSNO, PFICU, PFILSAN, PFLCU, PFLLSAN, PREANV, PRELSC, RH1, RH2, REEVAPCN, REEVAPLS, SEAICE{00..90}
  • INIT_DAO: Initialize MERRA met field arrays
  • IS_NEAR: Rewrote logic of #if block for clarity
  • INTERP: Rewrite #if block logic for clarity
  • CLEANUP_DAO: Deallocate MERRA met field arrays
dust_dead_mod.f
  • Assign parameter FLX_MSS_FDG_FCT = 4.9d-4 for both MERRA and GEOS-5.
    (NOTE: We may need to eventually rescale this.)
fast_j.f
  • Do cloud overlapping for MERRA the same way as for GEOS-5
gamap_mod.f
  • INIT_TRACERINFO: Define units of CMFMC field w/ same units as GEOS-5
global_ch4_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
global_hno3_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
global_o3_mod.f
  • Rewrote logic of #if block, now treat MERRA in the same way as GEOS-5
input_mod.f
  • READ_SIMULATION_MENU: Read value for MERRA_DIR from input.geos file
land_mercury_mod.f
  • Added #elif defined( MERRA ) section to all #if blocks. For now, treat MERRA in the same way as for GEOS-5.
lightning_nox_mod.f
  • LIGHTNING: Eliminate the shallow-cloud inhibititon trap for MERRA, as we already do for GEOS-5
  • GET_OTD_LIS_SCALE: Compute ANN_AVG_FLASHRATE for MERRA in the same way as for GEOS-5.
    (NOTE: We may have to rescale this in the future.)
Makefile
  • Added dependencies for merra_cn_mod.f
main.f
  • Read RH from disk, in the same way as for GEOS-5.
    (NOTE: MERRA RH is a 6-hr instantaneous field; GEOS-5 RH is 6-hr average field.)
  • Rewrote #if block logic where met fields are read in from disk
  • Now calls routines from merra_cn_mod.f, merra_a1_mod.f, merra_a3_mod.f, merra_i6_mod.f to read in met data
mercury_mod.f
  • Added   #elif defined( MERRA )   section to all #if blocks. For now, treat MERRA in the same way as for GEOS-5.
merra_a1_mod.f
  • New module. Reads in the MERRA 1-hour time-averaged (aka "A1") fields from disk.
merra_a3_mod.f
  • New module. Reads in the MERRA 3-hour time-averaged (aka "A3") fields from disk.
merra_cn_mod.f
  • New module. Reads in the MERRA constant (aka "CN") fields from disk.
merra_i6_mod.f
  • New module. Reads in the MERRA 6-hour instantaneous (aka "I6") fields from disk.
nei2005_anthro_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
schem.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
tagged_co_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
upbdflx_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )
vdiff_mod.f90
  • Added   #elif defined( MERRA )   section to all #if blocks. For now, treat MERRA in the same way as for GEOS-5.
wetscav_mod.f
  • Change instances of #if defined( GEOS_5 )   to   #if defined( GEOS_5 ) || defined( MERRA )

--Bob Y. 13:50, 18 August 2010 (EDT)

Outstanding issues

Lightning

For the time being, GEOS-Chem/MERRA will read in the same the OTD/LIS redistribution factors as for GEOS-5. MERRA is based on GEOS-5.2.0, so this should be OK for a first-cut.

However, for proper treatment, the OTD/LIS redistribution factors for MERRA will be rescaled for the entire OTD/LIS observation period. This cannot be done until we have processed and regridded several years of MERRA met data.

Wet deposition and scavenging

We are currently looking into how some of the MERRA precipitation fields can be used to improve the existing GEOS-Chem wet scavenging algorithm.

Acetone ocean source

As a first cut, the ocean source of acetone for MERRA (computed in routine OCEAN_SOURCE_ACET in acetone_mod.f) is computed in the same way as for GEOS-5. The following #if block was based on the GEOS-5 code:

#elif defined( MERRA )

      !%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      !%%% NOTE: Treat MERRA in the same way as GEOS-5, although    %%%
      !%%% we may want to rescale this in the future (bmy, 8/13/10) %%%
      !%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

#if defined( GRID4x5 )
      REAL*8, PARAMETER :: SCALE_FACTOR = 0.9551d0   ! MERRA 4x5
#elif defined( GRID2x25 )
      REAL*8, PARAMETER :: SCALE_FACTOR = 0.2212d0   ! MERRA 2x25
#endif

At some point we may need to rescale this. However this cannot be done until we have sufficient MERRA met fields processed and regridded.

--Bob Y. 15:03, 16 August 2010 (EDT)