Difference between revisions of "Photolysis mechanism"

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(→‎O1D reaction updated to JPL 2006)
(→‎Cloud overlap options in FAST-J)
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GEOS-Chem now has 3 cloud overlap options in the FAST-J photolysis mechanism:
 
GEOS-Chem now has 3 cloud overlap options in the FAST-J photolysis mechanism:
  
−
# Linear cloud overlap assumption:
+
1. Linear cloud overlap assumption.  This is the default in GEOS-Chem versions [GEOS-Chem_versions_under_development#v8-01-01|v8-01-01]] and prior.  The option is:
  
−
  Grid Box Optical depth = In-cloud optical depth * Cloud fraction
+
  Grid Box Optical depth = In-cloud optical depth * Cloud fraction.  This is the default
  
−
This
 
  
−
# Approximate random overlap assumption:
+
2. Approximate random overlap assumption: This option will be introduced into the standard code in GEOS-Chem v8-01-02 (benchmark run #1).
  
−
            !===========================================================
+
Grid Box Optical Depth = In-Cloud Optical Depth * ( Cloud Fraction )^1.5
−
            ! CLOUD OVERLAP : LINEAR ASSUMPTION
+
−
            ! Directly use OPTDEPTH = TAUCLD * CLDTOT
+
−
            !
+
−
            ! NOTE: Use this option if you want to compare to results
+
−
            !      from GEOS-Chem v7-04-12 and prior versions.
+
−
            !===========================================================
+
−
            IF ( OVERLAP == 1 ) then
+
  
−
              ! Call FAST-J routines to compute J-values
+
3. Maximum random overlap assumption: This option is much more computationally intensive, and therefore is not used as the default option. However, if you wish to use this option, then manually edit the <tt>fast_j.f</tt> source code file such that <tt>OVERLAP = 3</tt>. 
−
              CALL PHOTOJ( NLON, NLAT, YLAT,    DAY_OF_YR,   
+
−
    &                      MONTH, DAY,  CSZA,    TEMP,   
+
−
    &                      SFCA,  OPTD, OPTDUST, OPTAER )
+
  
−
            !===========================================================
+
The Maximum-Random Overlap (MRAN) scheme assumes that clouds in adjacent layers are maximally overlapped to form a cloud block and that blocks of clouds separated by clear layers are randomly overlapped.  A vertical profile of fractional cloudiness is converted into a series of column configurations with corresponding fractions see Liu et al., JGR 2006; hyl,3/3/04).
−
            ! CLOUD OVERLAP : APPROXIMATE RANDOM OVERLAP
+
−
            ! Use OPTDEPTH = TAUCLD * CLDTOT**1.5
+
−
            !===========================================================
+
−
            ELSE IF ( OVERLAP == 2 ) THEN
+
  
−
              ! Column cloud fraction (not less than zero)
+
For more details about cloud overlap assumptions and their effect on photolysis frequencies and key oxidants in the troposphere, refer to the following articles:
−
              CLDF1D = CLDF(1:LLPAR,NLON,NLAT)
+
−
              WHERE ( CLDF1D < 0d0 ) CLDF1D = 0d0
+
−
             
+
−
              ! Adjust optical depth
+
−
              OPTD = OPTD * SQRT( CLDF1D )
+
  
−
              ! Call FAST-J routines to compute J-values
+
#Liu, H., et al., ''Radiative effect of clouds on tropospheric chemistry in a global three-dimensional chemical transport model'', <u>J. Geophys. Res.</u>, '''111''', D20303, doi:10.1029/2005JD006403, 2006.
−
              CALL PHOTOJ( NLON,  NLAT, YLAT,    DAY_OF_YR, 
+
#Tie, X., et al., ''Effect of clouds on photolysis and oxidants in the troposphere, <u>J. Geophys. Res.</u>, ''108''(D20), 4642, doi:10.1029/2003JD003659, 2003.
−
    &                      MONTH, DAY,  CSZA,    TEMP, 
+
#Feng, Y., et al., ''Effects of cloud overlap in photochemical models'', <u>J. Geophys. Res.</u>, ''109'', D04310, doi:10.1029/2003JD004040, 2004.
−
    &                      SFCA,  OPTD, OPTDUST, OPTAER )
+
#Stubenrauch, C.J., et al., ''Implementation of subgrid cloud vertical structure inside a GCM and its effect on the radiation budget'', <u>J. Clim.</u>, 10, 273-287, 1997.
−
 
+
−
            !===========================================================
+
−
            ! CLOUD OVERLAP : MAXIMUM RANDOM OVERLAP
+
−
            !
+
−
            ! The Maximum-Random Overlap (MRAN) scheme assumes that
+
−
            ! clouds in adjacent layers are maximally overlapped to
+
−
            ! form a cloud block and that blocks of clouds separated by
+
−
            ! clear layers are randomly overlapped.  A vertical profile
+
−
            ! of fractional cloudiness is converted into a series of
+
−
            ! column configurations with corresponding fractions
+
−
            ! (see Liu et al., JGR 2006; hyl,3/3/04).
+
−
            !
+
−
            ! For more details about cloud overlap assumptions and
+
−
            ! their effect on photolysis frequencies and key oxidants
+
−
            ! in the troposphere, refer to the following articles:
+
−
            !
+
−
            ! (1) Liu, H., et al., Radiative effect of clouds on  
+
−
            !      tropospheric chemistry in a global three-dimensional  
+
−
            !      chemical transport model, J. Geophys. Res., vol.111,  
+
−
            !      D20303, doi:10.1029/2005JD006403, 2006.
+
−
            ! (2) Tie, X., et al., Effect of clouds on photolysis and  
+
−
            !      oxidants in the troposphere, J. Geophys. Res.,  
+
−
            !      108(D20), 4642, doi:10.1029/2003JD003659, 2003.
+
−
            ! (3) Feng, Y., et al., Effects of cloud overlap in  
+
−
            !      photochemical models, J. Geophys. Res., 109,  
+
−
            !      D04310, doi:10.1029/2003JD004040, 2004.
+
−
            ! (4) Stubenrauch, C.J., et al., Implementation of subgrid  
+
−
            !      cloud vertical structure inside a GCM and its effect  
+
−
            !      on the radiation budget, J. Clim., 10, 273-287, 1997.
+
−
            !-----------------------------------------------------------
+
−
            ! MMRAN needs IN-CLOUD optical depth (ODNEW) as input
+
−
            ! Use cloud fraction, instead of OPTD, to form cloud blocks
+
−
            ! (hyl,06/19/04)
+
−
            !===========================================================
+

Revision as of 16:31, 23 May 2008

This page describes some of the updates to the FAST-J photolysis mechanism, as is currently implemented in GEOS-Chem.

Input files for FAST-J

The following input files are required for the FAST-J photolysis mechanism:

ratj.d
This file is where you specify each of the FAST-J photolysis species. Each species is mapped to a corresponding entry of the GEOS-Chem chemical mechanism.
jv_atms.dat
This file specifies the reference O3 climatology for FAST-J. NOTE: GEOS-Chem will overwrite this reference climatology with TOMS/SBUV data for those months and locations where such data exists.
jv_spec.dat
This file is where the various quantum yields and aerosol cross-sections are specified.

O1D reaction updated to JPL 2006

As of GEOS-Chem v8-01-02, the rate constants in the "FAST-J" jv_atms.dat file have been updated by Lin Zhang.

These were the old values: 

O3_1d  180 9.000E-01 9.000E-01 3.824E-01 8.092E-02 7.650E-02       0.0       0.0
O3_1d  260 9.000E-01 9.000E-01 4.531E-01 1.438E-01 7.654E-02       0.0       0.0
O3_1d  300 9.000E-01 9.000E-01 5.273E-01 2.395E-01 7.659E-02       0.0       0.0

which are now replaced by the new values from JPL 2006: 

O3_1d  180 9.000E-01 9.000E-01 3.824E-01 8.092E-02 7.650E-02       0.0       0.0
O3_1d  260 9.000E-01 9.000E-01 4.531E-01 1.438E-01 7.654E-02       0.0       0.0
O3_1d  300 9.000E-01 9.000E-01 5.273E-01 2.395E-01 7.659E-02       0.0       0.0

For more information, please contact Lin Zhang (lzh@io.as.harvard.edu).

--Bob Y. 11:16, 23 May 2008 (EDT)

Cloud overlap options in FAST-J

GEOS-Chem now has 3 cloud overlap options in the FAST-J photolysis mechanism:

1. Linear cloud overlap assumption. This is the default in GEOS-Chem versions [GEOS-Chem_versions_under_development#v8-01-01|v8-01-01]] and prior. The option is: 

Grid Box Optical depth = In-cloud optical depth * Cloud fraction.  This is the default


2. Approximate random overlap assumption: This option will be introduced into the standard code in GEOS-Chem v8-01-02 (benchmark run #1). 

Grid Box Optical Depth = In-Cloud Optical Depth * ( Cloud Fraction )^1.5

3. Maximum random overlap assumption: This option is much more computationally intensive, and therefore is not used as the default option. However, if you wish to use this option, then manually edit the fast_j.f source code file such that OVERLAP = 3.

The Maximum-Random Overlap (MRAN) scheme assumes that clouds in adjacent layers are maximally overlapped to form a cloud block and that blocks of clouds separated by clear layers are randomly overlapped. A vertical profile of fractional cloudiness is converted into a series of column configurations with corresponding fractions see Liu et al., JGR 2006; hyl,3/3/04).

For more details about cloud overlap assumptions and their effect on photolysis frequencies and key oxidants in the troposphere, refer to the following articles:

  1. Liu, H., et al., Radiative effect of clouds on tropospheric chemistry in a global three-dimensional chemical transport model, J. Geophys. Res., 111, D20303, doi:10.1029/2005JD006403, 2006.
  2. Tie, X., et al., Effect of clouds on photolysis and oxidants in the troposphere, J. Geophys. Res., 108(D20), 4642, doi:10.1029/2003JD003659, 2003.
  3. Feng, Y., et al., Effects of cloud overlap in photochemical models, J. Geophys. Res., 109, D04310, doi:10.1029/2003JD004040, 2004.
  4. Stubenrauch, C.J., et al., Implementation of subgrid cloud vertical structure inside a GCM and its effect on the radiation budget, J. Clim., 10, 273-287, 1997.
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