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.
- The MERRA high-resolution grid (0.5° x 0.666°) is identical to that of GEOS-5.
- The MERRAvertical grid (72 hybrid levels) is identical to that of GEOS-5.
- 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:
- 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)
- 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) in MERRA was missing coverage over Antarctica and Greenland.
- 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:
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
|
- In routine GET_MODELNAME: Add "MERRA_47L" and "MERRA" modelnames to the #if block
- In routine GET_NAME_EXT: Return grid name "geos5" for MERRA fields
|
| directory_mod.f
|
- Added MERRA_DIR variable for MERRA met fields
|
| file_mod.f
|
- Add IU_A1 parameter for logical unit # of MERRA 1hr time avg'd data
- In routine CLOSE_FILES: Now close the IU_A1 logical unit #
|
| pressure_mod.f
|
- In routine GET_PRESSURE: Compute PEDGE for MERRA in the same way as for GEOS-5
- In routine 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
- Add routine ITS_TIME_FOR_A1
- Update comments in various places
|
| 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
|
- In routine 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
|
- In routine 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}
- In routine COPY_I6_FIELDS: Rewrote #if block for clarity; Now copy MERRA RH fields
- In routine INIT_DAO: Initialize MERRA met field arrays
- In routine IS_ICE: Changed #if block line to #elif defined( GEOS_4 ) || defined( GEOS_5 ) || defined( MERRA )
- In routine IS_LAND: Changed #if block line to #elif defined( GEOS_4 ) || defined( GEOS_5 ) || defined( MERRA )
- In routine IS_NEAR: Rewrote logic of #if block for clarity
- In routine IS_WATER: Changed #if block line to #elif defined( GEOS_4 ) || defined( GEOS_5 ) || defined( MERRA )
- In routine INTERP: Rewrite #if block logic for clarity
- In routine CLEANUP_DAO: Deallocate MERRA met field arrays
|
| depo_mercury_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| diag3.f
|
- Modify ND66 diagnostic to divide by proper # of increments (i.e. every 3 hours)
- Modify ND67 diagnostic to divide by proper # of increments (i.e. every hour)
|
| dust_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| 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
|
- In routine 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
|
| initialize.f
|
- Now also reset the counter for A1 timesteps by calling routine SET_CT_A1( RESET=.TRUE. ) from time_mod.f
|
| input_mod.f
|
- In routine READ_SIMULATION_MENU: Read value for MERRA_DIR from input.geos file
|
| land_mercury_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| lightning_nox_mod.f
|
- In routine LIGHTNING: Eliminate the shallow-cloud inhibititon trap for MERRA, as we already do for GEOS-5
- In routine 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
- Added dependencies for merra_a1_mod.f
- Added dependencies for merra_a3_mod.f
- Added dependencies for merra_i6_mod.f
|
| main.f
|
- Rewrote #if block logic where met fields are read in from disk
- 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.)
- 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
- Now compute lightning emissions every 3 hours (immediately after reading in the A3 fields).
|
| megan_mod.f
|
- At top of module:
- Move the #include "CMN_SIZE" declaration to top of module
- For MERRA only: define DAY_DIM parameter = 24 for hourly temperature data
- For all other met data: define DAY_DIM parameter = 8 for 3-hourly temperature data
- In routine INIT_MEGAN:
- For MERRA only: call routines OPEN_MERRA_A1_FIELDS and READ_MERRA_A1_FIELDS every hour
- For all other met data: call routines OPEN_A3_FIELDS and READ_A3_FIELDS every 3 hours
|
| mercury_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| 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 )
|
| sulfate_mod.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
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| wetscav_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
GeosTomas directory
The following modifications for MERRA were made in the GeosTomas/ directory:
| File
|
Modifications made
|
| Makefile
|
- Added dependencies for merra_cn_mod.f
- Added dependencies for merra_a1_mod.f
- Added dependencies for merra_a3_mod.f
- Added dependencies for merra_i6_mod.f
|
| diag3.f
|
- Modify ND66 diagnostic to divide by proper # of increments (i.e. every 3 hours)
- Modify ND67 diagnostic to divide by proper # of increments (i.e. every hour)
|
| dust_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| gamap_mod.f
|
- In routine INIT_TRACERINFO: Define units of CMFMC field w/ same units as GEOS-5
|
| input_mod.f
|
- In routine READ_SIMULATION_MENU: Read value for MERRA_DIR from input.geos file
|
| sulfate_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
| wetscav_mod.f
|
- Change instances of #if defined( GEOS_5 ) to #if defined( GEOS_5 ) || defined( MERRA )
|
--Bob Y. 12:20, 26 August 2010 (EDT)
Resolved issues
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)
