MERRA-2 implementation details

Overview

MERRA2 is the newest reanalysis meteorological data product from NASA/GMAO. It is created with the NASA/GMAO GEOS Data Assimilation System (aka GEOS-DAS), version 5.12.4. Overall, the structure of MERRA2 is very similar to the GMAO "forward processing" data product, which we refer to as GEOS-FP. Therefore, within GEOS-Chem we can (for the most part) treat MERRA2 in the same way as we do for the GEOS_FP.

Comparing MERRA2 to other GMAO met data products

The table below compares many features of MERRA2 with other GMAO met data products:

Feature	MERRA2	GEOS-FP	MERRA	GEOS-5
Native vertical grid	0.5° lat x 0.625° lon	0.25° lat x 0.3125° lon	0.5° lat x 0.667° lon (surface fields) 1° lat x 1.25° lon (most 3D fields) 1.25° x 1.25° lon (moist quantities)	0.5° lat x 0.667° lon
Native horizontal grid	72 hybrid levels	Same as MERRA2	Same as MERRA2	Same as MERRA2
Time-invariant fields	FRLAKE FRLAND FRLANDIC(E) FROCEAN PHIS	Same as MERRA2	Same as MERRA2	Same as MERRA2
Time archiving: surface fields	A1 (1-hr time averaged)	Same as MERRA2	Same as MERRA2	A3 (6-hr time average)
Time archiving: 3D fields	A3 (3-hr time averaged) I3 (3-hr instantaneous)	Same as MERRA2 Same as MERRA2	A3 (3-hr time average) I6 (6-hour instantaneous)	A6 (6-hr time average) and I6 (6-hr instantaneous)
Timestamps	See this wiki page	See this wiki page	See this wiki page	See this wiki page
Precipitation fields	DQRCU, DQRLSAN, PFICU, PFILSAN, PFLCU, PFLLSAN, REEVAPCN, REEVAPLSAN	Same as MERRA2	Same as MERRA2	DQIDTMST DQLDTMST DQVDTMST MOISTQ = DQIDTMST + DQLDTMST + DQVDTMST
Temperature	T [K] I3 (3-hr instantaneous)	Same as MERRA2 Same as MERRA2	Same as MERRA2 A3 (6-hr time average)	Same as MERRA2 A6 (6-hr time average)
Relative humidity	RH [1] A3 (3-hr time average)	Same as MERRA2 Same as MERRA2	Same as MERRA2 I3 (6-hr instantaneous)	Same as MERRA2 A6 (6-hr time-averaged)
Specific humidity	QV [kg kg-1] I3 (3-hr instantaneous)	Same as MERRA2 Same as MERRA2	Same as MERRA2 A3 (3-hr time average)	Same as MERRA2 A6 (6-hr time-averaged)
Vertical pressure velocity	OMEGA [Pa s-1] A3 (3-hr time average)	Same as MERRA2 Same as MERRA2	Same as MERRA2 I6 (6-hr instantaneous)	Same as MERRA2 A6 (6-hr time-averaged)
Ertel potential vorticity	PV [K m2 kg-1 s-1] A1 (1-hr time average)	Same as MERRA2 Same as MERRA2	Same as MERRA2 I6 (6-hr instantaneous)	Same as MERRA2 A6 (3-hr time-average)
Snow mass	SNOMAS [kg/m2] A1 (3-hr time average) Missing coverage at poles is now corrected, as per MERRA	Same as MERRA2 Same as MERRA2 Same as MERRA2	Same as MERRA2 Same as MERRA2 Same as MERRA2	SNOMAS [m] A3 (3-hr time average)
Sea level pressure	SLP [Pa] A1 (1-hr time average) Converted to hPa when read from disk	SLP [hPa] Same as MERRA2	SLP [hPa] Same as MERRA2	SLP [hPa] I6 (3-hr instantaneous)
Surface pressure	PS [Pa] I3 (3-hr instantaneous) Converted to hPa when read from disk	PS [hPa] I3 (3-hr instantaneous)	PS [hPa] I6 (6-hr instantaneous)	PS [hPa] I6 (3-hr instantaneous)
Tropopause pressure	TROPPT [Pa] A1 (1-hr time average) Converted to hPa when read from disk	TROPPT [hPa] Same as MERRA2	TROPPT [hPa] Same as MERRA2	TROPP [hPa] A3 (3-hr time average)
GEOS-Chem convection routine	DO_MERRA_CONVECTION (in convection_mod.F)	Same as MERRA2	Same as MERRA2	NFCLDMX (in convection_mod.F)
GEOS-Chem wet deposition routine	WETDEP_MERRA (wetscav_mod.F)	Same as MERRA2	Same as MERRA2	WETDEP (wetscav_mod.F)
GEOS-Chem transport routine	TPCORE_FVDAS (tpcore_fvdas_mod.F90)	Same as MERRA2	Same as MERRA2	Same as MERRA2
File format read by GEOS-Chem	netCDF-4	netCDF-3	binary	binary

--Bob Y. (talk) 16:41, 17 August 2015 (UTC)

Timeline for integration into GEOS-Chem

As of this writing, we have we have modified GEOS-Chem (as described below) so that it can be driven by the new NASA/GMAO MERRA2 reanalysis data product. These source code updates were validated in with the 1-month benchmark simulation v11-01c and approved on 14 Sept 2015.

Currently, several of the GEOS-Chem specialty simulations are already compatible with MERRA2. These include:

• CO2 simulation
• CH4 simulation
• Hg simulation (but some tuning factors for nested grids are still needed)
• POPs simulation
• Rn-Pb-Be simulation
• Tagged O3 simulation

Making the various "full-chemistry simulations" (i.e. those using the benchmark, UCX, SOA, and tropchem chemistry mechanisms) compatible with MERRA2 will take longer. These "full-chemistry" simulations use emissions (e.g. lightning, dust) that have scale factors that must be tuned specifically for each met field product. In order to do this tuning, we have to have at least 1 or more years of MERRA2 met data processed and saved to disk.

For more information about MERRA2, please see these resources:

• MERRA2 page on the GEOS-Chem wiki
• List of MERRA2 met fields used for GEOS-Chem
• Version history of GMAO met data products
• Comparing MERRA2 to other GMAO met data products

--Bob Y. (talk) 14:54, 18 August 2015 (UTC)

Required coding changes in GEOS-Chem

As noted in the section above, the similarities between MERRA2 and GEOS-FP (especially of the vertical grids) means that in most cases we can just treat MERRA2 in the same way as for GEOS-FP. 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 ) || defined( MERRA ) || defined( GEOS_FP )

to

#if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )

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 MERRA2:

Top-level directory

The following modifications for MERRA2 were made in the root GEOS-Chem directory:

File	Modifications made
Makefile_header.mk	If MET=merra2 or MET=merra-2 (case-insensitive), then activate the MERRA2 C-preprocessor switch i.e. Add -DMERRA2 to the Makefile variable USER_DEFS. If GRID=05x0625 is added, then activate the GRID05x0625 C-preprocessor switch i.e. Add -DGRID05x0625 to the Makefile variable USER_DEFS.

--Bob Y. (talk) 18:28, 12 August 2015 (UTC)

Headers directory

The following modifications for MERRA2 were made in the Headers/ directory:

File	Modifications made
CMN_SIZE_mod.F	Added size parameters for GEOS-FP grids at 4° x 5°, 2° x 2.5°, and 0.25° x 0.3125° resolution
gigc_input_opt_mod.F90	Add MERRA2_DIR to the OptInput derived type Set Input_Opt%MERRA2_DIR = './' in routine Init_GIGC_Input_Opt
gigc_state_met_mod.F90	Multiple instances: Now use: #if defined( GEOS_FP ) || defined( MERRA ) || defined( MERRA2 )

--Bob Y. (talk) 18:28, 12 August 2015 (UTC)

GeosUtil directory

The following modifications for MERRA2 were made in the GeosUtil/ directory:

File	Modifications made
bpch2_mod.F	In routine GET_MODELNAME: Add MERRA2_47L and MERRA2 modelnames to the #if block In routine GET_NAME_EXT: Return grid name merra2 for MERRA2 fields In routine GET_NAME_EXT_2D: Now use #if defined( MERRA ) || defined( MERRA2 ) In routine GET_RES_EXT: Return resolution string 05x0625 for 0.5° x 0.625° grids
pressure_mod.F	In routines GET_PEDGE and GET_PEDGE_FULLGRID: Compute PEDGE for MERRA2 in the same way as for GEOS-5, MERRA, and GEOS-FP In routine INIT_PRESSURE: Initialize Ap and Bp for MERRA2 in the same way as for GEOS-5, MERRA, and GEOS-FP
time_mod.F	In routine GET_A1_TIME: Compute the DATE array for MERRA2 the same way as is done for MERRA and GEOS-FP
transfer_mod.F	In routine INIT_TRANSFER: Set L_COPY = 36 for MERRA2 Changed code to #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In several routines: Changed code to #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )

--Bob Y. (talk) 20:33, 12 August 2015 (UTC)

GeosCore directory

The following modifications for MERRA2 were made in the GeosCore/ directory:

File	Modifications made
calcrate.F	Multiple instances: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
carbon_mod.F	Multiple instances: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
cldice_HbrHOBr_mod.F	Multiple instances: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
convection_mod.F	In routine DO_CONVECTION: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routine DO_MERRA_CONVECTION: Changed code to #if defined( GEOS_FP ) || defined( MERRA2 ) where we set PFICU and PFLCU
dao_mod.F	In routine COPY_I6_FIELDS: Changed code to: #if defined( GEOS_FP ) || defined( MERRA2 ) In routine INTERP: Changed code to: #if defined( GEOS_FP ) || defined( MERRA2 )
depo_mercury_mod.F	In routine ADD_Hg2_SNOWPACK Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
dao_mod.F	In routine COPY_I6_FIELDS: Changed code to: #if defined( GEOS_FP ) || defined( MERRA2 ) In routine INTERP: Changed code to: #if defined( GEOS_FP ) || defined( MERRA2 )
diag3.F	Multiple instances: Changed code to: #if defined( GEOS_FP ) || defined( MERRA2 ), etc.
dust_dead_mod.F	In routine DST_MBL: For GEOS-FP, add a new value for parameter FLX_MSS_FDG_FCT. The scale factor ensures that we get the same dust totals (w/in roundoff error) as for GEOS-5.
fast_jx_mod.F	In routine FAST_JX: Do cloud overlapping for GEOS-FP in the same way as for GEOS-5 and MERRA. Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
gamap_mod.F	In routine INIT_TRACERINFO: Changed code to: #elif defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP )
global_ch4_mod.F	In routines WETLAND_EMIS and READ_COPROD: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP )
input_mod.F	In routine READ_SIMULATION_MENU: Now read value for Input_Opt%MERRA2_DIR from input.geos Also set Input_Opt%RES_DIR accordingly for 0.5° x 0.625° nested grids Set LUNZIP=.FALSE. for MERRA2 met In routine READ_CONVECTION_MENU: Change #if statement to allow non-local PBL mixing for MERRA2 met data In routine VALIDATE_DIRECTORIES: Error check MERRA2_DIR for start & end date
land_mercury_mod.F	In routines LAND_MERCURY_FLUX: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routines SOILEMIS: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) Extend #if statement for variable SOIL_EMIS_FAC to get the code to compile w/o error. Team Hg will need to supply an updated value later on.
main.F	In main.F: Changed code to if defined( GEOS_FP ) || defined( MERRA2 ) where we define N_DYN_STEPS Changed code to if defined( GEOS_FP ) || defined( MERRA2 ) where we define Input_Opt%USE_O3_FROM_MET In included routine READ_INITIAL_MET_FIELDS: Added calls to routines from merra2_read_mod.F90 In included routine READ_MET_FIELDS: Added calls to routines from merra2_read_mod.F90
mercury_mod.F	In routine CHEMMERCURY: Add placeholder K_RED_JNO2 parameter for the 0.5° x 0.625° nested grids. For now use the same value as for the 0.5° x 0.666° grid. Team Hg will need to supply an updated value later on. Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
merra2_read_mod.F90	Added this module w/ routines to read GEOS-FP met data (in netCDF format)
ocean_mercury_mod.F	Multiple instances: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
planeflight_mod.F	In routine PLANEFLIGHT Now use: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
strat_chem_mod.F90	Multiple instances: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routine DO_SYNOZ: Add placeholder values for 0.5° x 0.625° grids
sulfate_mod.F	In routine CHEM_SO2: Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routine INIT_SULFATE: Changed code to: #if !defined( GEOS_5 ) && !defined( MERRA ) && !defined( GEOS_FP ) && !defined( MERRA2 ) In routine SRCSFC30 (TOMAS-only): Added a placeholder value for TSCALE for the 0.5° x 0.625° grids
tagged_ox_mod.F	In routine GET_REGIONAL_POX: Now use: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
tpcore_bc_mod.F:	Multiple instances: Added MERRA2 placeholder values for I1_BC_CH, I2_BC_CH, J1_BC_CH, J2_BC_CH Added MERRA2 placeholder values for I1_BC_EU, I2_BC_EU, J1_BC_EU, J2_BC_EU Added MERRA2 placeholder values for I1_BC_NA, I2_BC_NA, J1_BC_NA, J2_BC_NA
vdiff_mod.F90	In routine VDIFFDR: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
wetscav_mod.F	In routine DO_WETDEP: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routine DO_WASHOUT_ONLY:: Changed code to: #if defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 ) In routine MAKE_QQ: Changed code to: #defined( GEOS_FP ) || defined( MERRA2 ) In routine RAINOUT: Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )

--Bob Y. (talk) 18:29, 12 August 2015 (UTC)

HEMCO/Core directory

The following modifications for MERRA2 were made in the HEMCO/Core directory:

File	Modifications made
hco_chartools_mod.F90	At the top of the module: Extend the #ifdef statement to add the parameter DEF_MET = 'merra2' Extend the #ifdef statement to add the parameter DEF_RES = '05x0625'
hco_interp_mod.F90	In routine MODLEV_INTERPOLATE: Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )

--Bob Y. (talk) 18:28, 12 August 2015 (UTC)

HEMCO/Extensions directory

The following modifications for MERRA2 were made in the HEMCO/Extensions directory:

File	Modifications made
hcox_ch4wetland_mod.F90	In routine WETLAND_EMIS: Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
hcox_dustdead_mod.F	In routine HCOX_DUSTDEAD_GETTUN: Add placeholder values of FLX_MSS_FDG_FCT = -999 for the MERRA2 2° x 2.5° and 4° x 5° grids. We will add the correct values once we can run simulations with at least a year of met data.
hcox_lightnox_mod.F	In routine GET_OTD_LIS_SCALE: Add placeholder values of ANN_AVG_FLASHRATE for the MERRA2 0.5° x 0.625° grids. Add placeholder values of BETA for the MERRA2 2° x 2.5° and 4° x 5° grids. We will add the correct values once we can run simulations with at least a year of met data.
hcox_megan_mod.F	In routine GET_GAMMA_SM: Changed code to: #if defined( GEOS_5 ) || defined( MERRA ) || defined( GEOS_FP ) || defined( MERRA2 )
hcox_tomas_dustdead_mod.F	In routine HCOX_TOMAS_DUSTDEAD_GETTUN: Add placeholder values of FLX_MSS_FDG_FCT = -999 for the MERRA2 2° x 2.5° and 4° x 5° grids. We will add the correct values once we can run simulations with at least a year of met data.

--Bob Y. (talk) 18:53, 12 August 2015 (UTC)