Photolysis mechanism: Difference between revisions

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This page describes some of the updates to the FAST-J photolysis mechanism, as is currently implemented in GEOS-Chem.
Here we link to pages describing the various versions of the FAST-J and FAST-JX photolysis mechanisms used in GEOS-Chem.


== Input files for FAST-J ==
== Photolysis mechanisms used in standard GEOS-Chem versions ==


The following input files are required for the FAST-J photolysis mechanism:
The following photolysis mechanisms have been implemented in official releases of GEOS-Chem:


;[http://www.as.harvard.edu/ctm/geos/doc/man/chapter_5.html#5.4.1 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.
=== FAST-JX v7.0 ===
;[http://www.as.harvard.edu/ctm/geos/doc/man/chapter_5.html#5.4.2 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.
;[http://www.as.harvard.edu/ctm/geos/doc/man/chapter_5.html#5.4.3 jv_spec.dat]: This file is where the various quantum yields and aerosol cross-sections are specified.


== O1D reaction updated to JPL 2006 ==
The [[FAST-JX v7.0 photolysis mechanism]] is the newest version of the FAST-J software.  It was incorporated into [[GEOS-Chem v10-01]] by Sebastian Eastham (MIT) and the [[GEOS-Chem Support Team]], along with the [[UCX chemistry mechanism|UCX stratospheric-tropopsheric chemistry mechanism]].


As of [[GEOS-Chem_versions_under_development#v8-01-02|GEOS-Chem v8-01-02]], the rate constants in the "FAST-J" [http://www.as.harvard.edu/ctm/geos/doc/man/chapter_5.html#5.4.2 jv_atms.dat file] have been updated by Lin Zhang.
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 17:06, 16 November 2016 (UTC)


These were the old values:
=== FAST-J ===


O3_1d  180 9.500E-01 9.330E-01 4.270E-01 6.930E-02 6.060E-02      0.0      0.0
The [[FAST-J photolysis mechanism]] was used in GEOS-Chem versions prior to [[GEOS-Chem v10-01]].  It has since been replaced by [[FAST-JX v7.0 photolysis mechanism]].
O3_1d  260 9.500E-01 9.420E-01 4.890E-01 1.360E-01 7.110E-02      0.0      0.0
  O3_1d  300 9.500E-01 9.550E-01 5.870E-01 2.370E-01 8.570E-02      0.0       0.0


which are now replaced by the new values from JPL 2006:
--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 17:07, 16 November 2016 (UTC)


O3_1d  180 9.000E-01 9.000E-01 3.824E-01 8.092E-02 7.650E-02      0.0      0.0
== Photolysis mechanisms used in research versions of GEOS-Chem ==
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


Also the new file has the following header line (the O1D update is noted there):
The following photolysis mechanisms have been used in non-standard research versions of GEOS-Chem:


jv_spec.dat:  FAST-J, std JPL 00 (mje 4/02) -- aer/dust (rvm, 3/02) -- O1D (lzh 5/06)
=== FAST-JX v6.2 ===


For more information, please contact Lin Zhang (linzhang@fas.harvard.edu).
The [[FAST-JX v6.2 photolysis mechanism]] was implemented into several research versions of GEOS-Chem by Jingqiu Mao (Princeton). But this version of FAST-J was never incorporated into the standard GEOS-Chem model.


--[[User:Bmy|Bob Y.]] 13:00, 23 May 2008 (EDT)
--[[User:Bmy|Bob Y.]] 11:58, 20 May 2014 (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 === 
 
The linear cloud overlap option 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. 
 
=== Approximate random overlap assumption === 
 
This approximate random overlap 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
 
=== Maximum random overlap assumption ===
 
This maximum random overlap 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>. 
 
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:
 
#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.
#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.
#Feng, Y., et al., ''Effects of cloud overlap in photochemical models'', <u>J. Geophys. Res.</u>, '''109''', D04310, doi:10.1029/2003JD004040, 2004.
#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.
 
=== Discussion ===
 
'''''Hongyu Liu (hyl@nianet.org) wrote:'''''
 
:I have a comment about how the effect of cloud overlap in the vertical may be included in GEOS-Chem. The standard GEOS-Chem assumes linear scaling of cloud optical depth with cloud fraction in a grid box, i.e., the grid average cloud optical depth TAU' = TAU * f, where TAU is the COD in the cloudy portion of the grid and f is cloud fraction in the layer. This linear assumption (LIN) not only introduces a significant bias because of the nonlinear relationship between J-values and COD, but also is not consistent with the cloud-radiation interactions taking place in the original GEOS-DAS. Current GCMs or DAS usually use random overlap (RAN) or maximum-random overlap (MRAN) in their cloud-radiation packages.
 
:Ideally, GEOS-Chem should use the same cloud overlap assumption as the one used in GEOS-DAS where TOA radiative fluxes have been validated against e.g. satellite observations. But the ("exact") random overlap and MRAN approaches are computationally expensive. Fortunately, the so-called "approximate" random overlap scheme [TAU' = TAU * f^(3/2) which is computationally cheap] has been demonstrated to be a good approximation to both the "exact" random overlap and MRAN calculations. For details, see my GEOS-Chem cloud paper (section 2.3 & Figures 8d,9d:    http://research.nianet.org/~hyl/publications/liu2006_cloud1.abs.html
 
:So, if we don't want to use any cloud overlap assumptions because of computational cost, the "approximate" random overlap seems a good option - it makes more sense physically and is more consistent with the mother GCM or DAS.  Actually it has been used in the MOZART model for years [see Brasseur et al., 1998].
 
:Hongyu Liu
 
For more information, please contact Hongyu Liu (hyl@nianet.org).
 
--[[User:Bmy|Bob Y.]] 12:44, 23 May 2008 (EDT)

Latest revision as of 19:47, 2 January 2019

Here we link to pages describing the various versions of the FAST-J and FAST-JX photolysis mechanisms used in GEOS-Chem.

Photolysis mechanisms used in standard GEOS-Chem versions

The following photolysis mechanisms have been implemented in official releases of GEOS-Chem:

FAST-JX v7.0

The FAST-JX v7.0 photolysis mechanism is the newest version of the FAST-J software. It was incorporated into GEOS-Chem v10-01 by Sebastian Eastham (MIT) and the GEOS-Chem Support Team, along with the UCX stratospheric-tropopsheric chemistry mechanism.

--Bob Yantosca (talk) 17:06, 16 November 2016 (UTC)

FAST-J

The FAST-J photolysis mechanism was used in GEOS-Chem versions prior to GEOS-Chem v10-01. It has since been replaced by FAST-JX v7.0 photolysis mechanism.

--Bob Yantosca (talk) 17:07, 16 November 2016 (UTC)

Photolysis mechanisms used in research versions of GEOS-Chem

The following photolysis mechanisms have been used in non-standard research versions of GEOS-Chem:

FAST-JX v6.2

The FAST-JX v6.2 photolysis mechanism was implemented into several research versions of GEOS-Chem by Jingqiu Mao (Princeton). But this version of FAST-J was never incorporated into the standard GEOS-Chem model.

--Bob Y. 11:58, 20 May 2014 (EDT)

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