Difference between revisions of "Mean OH concentration"

Revision as of 16:11, 3 October 2013

On this page we track the evolution of the mean OH concentration in GEOS-Chem. This value is an indicator of how "hot" the chemistry is. Please also see the related topic about the methyl chloroform lifetime in GEOS-Chem.

Computation of the mean OH diagnostic

The mean OH diagnostic in GEOS-Chem is computed in diag_pl_mod.f.

Routine DO_DIAG_OH sums up the tropospheric air mass and mass-weighted OH mass after each call to the chemistry solver. The summing happens in these lines of code:

  ! Sum air mass term into AIR_MASS array
  XAIRMASS        = AIRDENS(JLOOP)    * VOLUME(JLOOP)
  AIR_MASS(I,J,L) = AIR_MASS(I,J,L)   + XAIRMASS

  ! Sum OH mass term into OH_MASS array
  XOHMASS         = CSPEC(JLOOP,IDOH) * XAIRMASS
  OH_MASS(I,J,L)  = OH_MASS(I,J,L)    + XOHMASS

where the arrays contain the following quantities:

  JLOOP             = 1-D array index for SMVGEAR
  I,J,L             = 3-D array indices
  AIRDENS(JLOOP)    = air density [molec/cm3]
  VOLUME(JLOOP)     = grid box volume [cm3]
  AIR_MASS(I,J,L)   = air mass [molec air]
  CSPEC(JLOOP,IDOH) = OH concentration [molec OH/cm3]  
  OH_MASS(I,J,L)    = mass-weighted OH = OH mass * air mass [molec OH/cm3 * molec air]

After the GEOS-Chem simulation finishes, the mean OH value is printed out in subroutines PRINT_MEAN_OH:

  ! Total Mass-weighted OH [molec OH/cm3] * [molec air]
  SUM_OHMASS = SUM( OH_MASS )

  ! Atmospheric air mass [molec air]
  SUM_MASS   = SUM( AIR_MASS ) 
         
  ! Divide OH [molec OH/cm3 * molec air] by [molec air] and report as [1e5 molec/cm3]
  OHCONC = ( SUM_OHMASS / SUM_MASS ) / 1d5

  ! Write value to log file
  WRITE( 6, '(/,a)' ) REPEAT( '=', 79 ) 
  WRITE( 6, *       ) 'ND23: Mass-Weighted OH Concentration'
  WRITE( 6, *       ) 'Mean OH = ', OHCONC, ' [1e5 molec/cm3]' 
  WRITE( 6, '(  a)' ) REPEAT( '=', 79 ) 
        

Typical values vary between 10⁵ - 11⁵ molec/cm3.

--Bob Y. 15:12, 11 February 2010 (EST)

Evolution of mean OH in GEOS-Chem

Table of mean OH values

The following table chronicles the evolution of the mean OH value from several different GEOS-Chem simulations. All benchmark simulations were conducted at 4 x 5 resolution unless noted otherwise.

--Bob Y. 16:32, 8 June 2011 (EDT)
--Melissa Payer 11:00, 1 June 2012 (EDT)

Additional documentation

GEOS-Chem version 8

• Differences in isoprene between v8-02-04-Run1 and v8-02-04-Run0
• Differences between MODIS LAI and AVHRR LAI

GEOS-Chem version 7

• Rynda Hudman investigated the changes in CO and O3 among benchmark simulations from v7-02-03 thru v7-04-12.
• List of differences in benchmark simulations between v7-02-03 and v7-04-02.
• List of differences in benchmark simulations between v7-04-02 and v7-04-12.
• Changes in anthropogenic NOx and CO from 1-yr benchmarks with versions v7-02-03 and v7-02-04
• Jennifer Logan looked at some of the differences between GEOS-3 and GEOS-4 in 1-year benchmark simulations.

--Bob Y. 09:32, 23 February 2010 (EST)

Plot of mean OH evolution in GEOS-Chem

Here is a plot of the mean OH concentration from several recent GEOS–Chem 1-year benchmark simulations. The mean OH is an indicator how the chemistry mechanism is performing. Typical values are 10–11 x 10⁵ molecules cm^-1.

NOTES:

1. Runs done with GEOS-3 met are denoted by squares; GEOS-4 met: triangles; GEOS-5 met: circles.
2. The large jump in mean OH between v8-01-04-Run2 and v8-02-01-Run0 is likely attributed to the photolysis rate updates for ketones and aldehydes. See this document about the new photolysis mechanism. However, we are still investigating this.
3. The runs done with GEOS-4 met have higher mean OH than the GEOS-3 and GEOS-5 runs because of the missing high cloud optical depth in the GEOS-4 met fields.
4. The large jump upward from v7-04-12-Run1 to v7-04-12-Run2 is attributed to a major upgrade of the lightning NOx algorithm. v7-04-12 was the first GEOS-Chem version to redistribute flashes regionally according to OTD/LIS statistics.
5. v7-04-13 uses the same lightning algorithm as in v7-04-12-Run2. However, the lightning flash redistribution according to OTD/LIS statistics was switched from regional to local redistribution.
6. v7-04-02-Run0 and v7-04-02-Run1 used GEIA biogenic emissions. v7-04-02-Run2 swiched to MEGAN biogenic emissions.

--Bob Y. 15:49, 24 February 2010 (EST)