Photolysis mechanism
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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 from 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
to these 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:
- Linear cloud overlap assumption:
Grid Box Optical depth = In-cloud optical depth * Cloud fraction
This
- Approximate random overlap assumption:
!===========================================================
! 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
CALL PHOTOJ( NLON, NLAT, YLAT, DAY_OF_YR,
& MONTH, DAY, CSZA, TEMP,
& SFCA, OPTD, OPTDUST, OPTAER )
!===========================================================
! CLOUD OVERLAP : APPROXIMATE RANDOM OVERLAP
! Use OPTDEPTH = TAUCLD * CLDTOT**1.5
!===========================================================
ELSE IF ( OVERLAP == 2 ) THEN
! Column cloud fraction (not less than zero)
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
CALL PHOTOJ( NLON, NLAT, YLAT, DAY_OF_YR,
& MONTH, DAY, CSZA, TEMP,
& SFCA, OPTD, OPTDUST, OPTAER )
!===========================================================
! 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)
!===========================================================