Mean OH concentration

From Geos-chem
Revision as of 19:33, 8 June 2011 by Bmy (Talk | contribs) (New page: 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 [[Met...)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

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.

Benchmark Met Fields & Year Mean OH
[105 molec cm-3] 		Change from
previous version
[105 molec cm-3] 		Important updates in this benchmark simulation References
v8-02-04-Run2 GEOS-5.1.0 2005 11.067 +0.019
(+0.17%)
  • Linoz stratospheric ozone chemistry used instead of SYNOZ scheme
v8-02-04-Run1 GEOS-5.1.0 2005 11.048 +0.598
(+5.72%)
  • MEGAN hybrid model with MODIS-derived LAI
v8-02-04-Run0 GEOS-5.1.0 2005 10.450 -1.362
(-11.53%)
  • MEGAN hybrid model with AVHRR-derived LAI
  • EPA/NEI2005 emissions
  • Non-local PBL mixing scheme
v8-02-01-Run0 GEOS-5.1.0 2005 11.812 +0.713
(+6.42%)
  • Updated chemical mechanism: globchem.dat
  • Updated photolysis rxn rates: jv_spec.dat, ratj.d
NOTE: there was a bug in near IR photolysis of HNO4 and HCHO in the jv_spec.dat and ratj.d files. This was finally resolved in v8-02-04. We recommend all users of v8-02-01, v8-02-02, and v8-02-03 to use these updated jv_spec.dat and ratj.d files.
v8-01-04-Run2 GEOS-5.1.0 2005 11.099 +0.805
(+7.82%)
v8-01-04-Run1 GEOS-5.0.1 2005 <tt>10.294 -0.395
(-3.69%)
  • Various emissions updates with regional overwrites
  • Aaron van Donkelaar et al scale factors for 2005
  • Switched from linear to random cloud overlap in FAST-J
v8-01-04-Run0 GEOS-5.0.1 2005 10.689 -1.351
(-11.22%)
v8-01-01-Run1 GEOS-5.0.1 2005 12.040 +0.034
(+0.28%)
  • Switched aerosol thermodynamical equilibrium scheme from ISORROPIA I to RPMARES
v8-01-01-Run0 GEOS-5.0.1 2005 12.006 -0.141
(-1.16%)
  • First simulation with GEOS-5 met data
v7-04-13-Run GEOS-4 2005 12.147 -0.669
(-5.22%)
v7-04-12-Run2 GEOS-4 2005 12.816 +1.053
(+8.95%)
  • Original non-near-land OTD/LIS local scaling
v7-04-12-Run1 GEOS-4 2005 11.763 -0.68
(-5.5%)
  • Ancient lightning scheme
v7-04-02-MEGAN GEOS-4 2001 12.44 -0.11
(-0.87%)
  • First benchmark w/ MEGAN biogenic emissions
v7-04-02-NOMEGAN GEOS-4 2001 12.55 +0.01
(+0.08%)
  • Switched fossil fuel scale year from 1995 to 1998
  • Last benchmark w/ the older GEIA biogenic emissions
v7-04-02-Base GEOS-4 2001 12.54 +0.67
(+5.6%)
  • 43 tracer simulation (no secondary organic aerosols)
  • Last 1-yr benchmark with fossil fuel scale year = 1995
v7-02-03-Run1 GEOS-4 2001 11.87 +1.39
(+13.26%)
  • Secondary organic aerosols (50 tracers)
  • GEOS-4 met fields
v7-02-03-Run0 GEOS-3 2001 10.48 ---
  • Secondary organic aerosols (50 tracers)
  • GEOS-3 met fields

--Bob Y. 11:17, 12 February 2010 (EST)

Additional documentation

GEOS-Chem version 8

GEOS-Chem version 7

--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.

File:Mean oh 1yr.png

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)

Retrieved from "https://wiki.seas.harvard.edu/geos-chem/index.php?title=Mean_OH_concentration&oldid=7055"