CH4 simulation

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This page contains information about the methane (CH4) simulation in GEOS-Chem.


Authors and collaborators

  • Bram Maasakkers (Harvard)
  • Alex Turner (Harvard)
  • Kevin Wecht (wecht [at] fas [dot] harvard [dot] edu) (Harvard)
  • Christopher Pickett-Heaps (formerly @ Harvard)
  • Jerome Drevet (formerly @ EPFL)
  • James Wang (formerly @ Harvard)

CH4 simulation user groups

User Group Personnel Projects
Harvard University Bram Maasakkers
Alex Turner
Kevin Wecht
North American methane sources

Notes about the methane simulation

1. The methane simulation uses monthly and annual average skin temperature and soil moisture values from the met fields. These are calculated offline using IDL (""). This file can be found on the ftp site in the methane data directory with the LPJ wetland emission scheme (e.g., "GEOS_0.5x0.666_NA/CH4_201305/wetlands"). The script should work as is for 2004-2011, however we don't currently have the met data for 2012 so you may need to modify "global_ch4_mod.F" if you're interested in 2012 or 2013.
Subroutine "WETLAND_EMIS"
        YEAR = GET_YEAR()
        #if   defined( GEOS_5 )
        IF ( YEAR .LT. 2004 ) YEAR  = 2004
        IF ( YEAR .GT. 2011 ) YEAR  = 2011
Subroutine "RICE_EMIS"
        ! Get annual and monthly mean soil wetness from GEOS
        ! One file contains both monthly and annual mean GWETTOP
        YEAR = GET_YEAR()
        #if   defined( GEOS_5 )
        IF ( YEAR .LT. 2004 ) YEAR  = 2004
        IF ( YEAR .GT. 2011 ) YEAR  = 2011
2. Seasonality of Rice Emissions: Seasonality in the rice emissions is imposed through annual and monthly average soil moisture values. This works reasonably well for major rice growing areas like South/East Asia where rice paddies are rain-fed, but it fails in other regions. For example, California rice paddies are irrigated and crops are grown in the summer, precisely when the natural soil is the driest. You can enter the "global_ch4_mod.F", subroutine "RICE_EMIS", and impose any seasonality you want on the annual emission rates from EDGAR.
3. Potential Global Mean Bias: The methane simulation may not simulate global average concentrations accurately. That is, you may have a mean bias of up to +/-30ppbv when you compare the simulation to observations. A global mean bias means that the model has a slight imbalance between the sources and sinks relative to the world. You may want to consider removing this mean bias before analyzing your model concentrations.

--Alex Turner 11:01, 24 January 2014 (EST)

Recent science updates

The following updates were recently added into the GEOS-Chem CH4 simulation:

Update CH4 emissions to EDGAR v4.2

This update was tested in the 1-month benchmark simulation v9-02m and approved on 30 Jul 2013. This update is included in Adjoint v35d.

Kevin Wecht has prepared EDGAR v4.2 emissions of methane for 2004-2008. The data files are available at:

You can download these directories with anonymous FTP or the Wget utility. For instructions, please see Chapter 2.4, Downloading the GEOS-Chem shared data directories in the GEOS-Chem Online User's Guide.

Modifications to subroutines RICE_EMIS and ASEASONAL_ANTHRO_EMIS in global_ch4_mod.F include changing the directory names and updating CYEAR and XTAU as follows:

     WRITE( CYEAR, '(i4)' ) GET_YEAR()
     XTAU = GET_TAU0( 1, 1, GET_YEAR() )

     IF ( GET_YEAR() .LT. 2004 )  THEN
        XTAU = GET_TAU0( 1, 1, 2004 )
     IF ( GET_YEAR() .GT. 2008 ) THEN
        XTAU = GET_TAU0( 1, 1, 2008 )

--Melissa Payer 16:53, 2 July 2013 (EDT)

Update methane emissions and add capability for North America nested grid

This update was tested in the 1-month benchmark simulation v9-01-03h and approved on 09 Mar 2012.

Kevin Wecht wrote:

I have some GEOS-Chem methane updates that I'd like to add to the standard code.
  1. GFED emissions - I've updated GFED-2 and GFED-3 biomass burning to include methane emissions.
  2. Methane simulation - I've updated emissions and error catches to make the simulation compatible with the nested simulation over North America. I added linearized CH4 chemistry from GMI output (CH4 loss frequencies generated by Lee Murray). These changes should be made to the data directory:
a. Replace Carbon_soil, Carbon_litter, and Wetfrac files in data directory (for all horizontal resolutions)
b. Add 2010-2011 TSKIN and GWETTOP files to data directory (for all horizontal resolutions)
c. Add nested north american OH files to OH directory
d. Add biofuel emissions to data directory (for all horizontal resolutions)
e. Add all emission files to data directory for nested North America simulation

The error in reading GWETTOP fields is also fixed in this update.

--Melissa Payer 17:35, 2 February 2012 (EST)




  1. Wecht, K.J., D.J. Jacob, C. Frankenberg, Z. Jiang, and D.R. Blake, Mapping of North America methane emissions with high spatial resolution by inversion of SCIAMACHY satellite data, submitted to J. Geophys. Res., 2014.
  2. Wecht, K.J., D.J. Jacob, M.P. Sulprizio, G.W. Santoni, S.C. Wofsy, R. Parker, H. Bösch, and J.R. Worden, Spatially resolving methane emissions in California: constraints from the CalNex aircraft campaign and from present (GOSAT, TES) and future (TROPOMI, geostationary) satellite observations, Atm. Chem. Phys. Discuss., 14, 4119-4198, doi:10.5194/acpd-14-4119-2014, 2014.
  3. Wecht, K.J., D.J. Jacob, S.C. Wofsy, E.A. Kort, J.R. Worden, S.S. Kulawik, D.K. Henze, M. Kopacz, and V.H. Payne, Validation of TES methane with HIPPO aircraft observations: implications for inverse modeling of methane sources, Atmos. Chem. Phys., 12, 1823-1832, 2012.

--Bob Y. 15:45, 9 April 2014 (EDT)

Previous issues that are now resolved

The following bugs and/or issues with the code have now been resolved:

Minor fixes to CH4 simulation for MERRA meteorology

These fixes are currently being validated in GEOS-Chem v10-01c.

We have made a couple of fixes to the CH4 simulation module (GeosCore/global_ch4_mod.F) for compatibility with the MERRA met fields. At lines 1114, and again at line 1503, there were #if blocks that looked like this:

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

but these should have been:

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

Furthermore, in data directory GEOS_4x5/CH4_201305/wetlands, we have symbolically linked files:

GWETTOP.geos5.4x5.YYYY.bpch --> GWETTOP.merra.4x5.YYYY.bpch
TSKIN.geos5.4x5.YYYY.bpch   --> TSKIN.merra.4x5.YYYY.bpch

where YYYY = { 2004, 2005, 2006, 2007, 2008, 2009, 2010 }.

These issues were discovered with the GEOS-Chem Unit Tester.

--Bob Y. 15:59, 9 April 2014 (EDT)

Fixes for wetland emissions

These issues were resolved during the public comment period following the provisional release of GEOS-Chem v9-02 and were included in the official release of GEOS-Chem v9-02 (03 Mar 2014).

Kevin Wecht wrote:

I have some updates/bug fixes to wetland emissions in the methane simulation. Both changes impact global_ch4_mod.F, subroutine WETLAND_EMIS.
1. Christopher Pickett-Heaps added a feature that zeroes wetland emissions if snow covers the ground. This was never incorporated into the standard code. It is included in the attached file.
2. Parameters in the subroutine are not correct. The following values are the correct and are included in the attached file:
          MOIST_SCALE = 0.205
          EMIT_FACT   = 0.018

--Melissa Sulprizio 16:11, 23 January 2014 (EST)
--Bob Y. 10:25, 4 April 2014 (EDT)

Error reading GWETTOP fields

This update was tested in the 1-month benchmark simulation v9-01-03h and approved on 09 Mar 2012.

There is a file read error in the current CH4 simulation. We will fix this issue in GEOS-Chem v9-01-03.

In RICE_EMIS (global_ch4_mod.F), XTAU is reset to the wrong value when GEWTTOP is read. Kevin Wecht provided a fix that accounts for different availabilities of GEOS-4 and GEOS-5 met fields. Prior to setting FILENAME for GWETTOP , add the following:

      YEAR = GET_YEAR()
#if   defined( GEOS_5 )
      IF ( YEAR .LT. 2004 ) YEAR  = 2004
      IF ( YEAR .GT. 2009 ) YEAR  = 2009
#elif defined( GEOS_4 )
      IF ( YEAR .LT. 2000 ) YEAR  = 2000
      IF ( YEAR .GT. 2006 ) YEAR  = 2006
      WRITE( CYEAR, '(i4)' ) YEAR
Also change:
     XTAU = GET_TAU0( 1, 1, GET_YEAR() )
     XTAU = GET_TAU0( GET_MONTH(), 1, GET_YEAR() )
     XTAU = GET_TAU0( 1, 1, YEAR )
     XTAU = GET_TAU0( GET_MONTH(), 1, YEAR )

--Melissa Payer 18:06, 2 February 2012 (EST)

Outstanding Issues

None reported so far.

--Bob Y. 14:07, 30 March 2012 (EDT)