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This Wiki attempts to provide some documentation for some exceptional knobs available in the Atmospheric Analysis.
This feature has been introduced in GSI quite some many years ago by Kim et al. 2018. Since it had gone untested for awhile it was found recently to be broken. Recenty, the code was revived and revised. Thanks to work done for the all-sky radiance assimilation (Y. Zhu, E. Liu, M.J. Kim, and others), the aerosol-affected radiance machinery is more general than that originally code, and now allowes the user to select specific channels, of given instruments, to be treated as sensitive to aerosols.
The following simple knobs trigger the use of aerosols in the CRTM brightness temperature similation:
Editing GSI_GridComp.rc.tmpl in the FVHOME/run directory, the line:
aero_bkg_filename: NONE # %s.abkg.eta.%y4%m2%d2_%h2%n2z.>>>NCSUFFIX<<<
should be reset to:
aero_bkg_filename: %s.abkg.eta.%y4%m2%d2_%h2%n2z.>>>NCSUFFIX<<<
The above implies the availability of aerosol-background fields, abkg.eta, files that will need to be read by GSI. These are to be treated as the meteorological, bkg.eta, are. That is, an experiment attempting to exercice the aerosol-affected radiance feature will need to provide restarts at the backgrond frequency, namely, files of the type abkgHH_eta_rst will need to be present in the recycle directory of the experiment (here HH means the hours from the model restart time).
The ultimate GSI trigger for ingesting aerosol fields into the analysis is found in the anavinfo file, more specifically, the file in the FVHOME/run directory called, gmao_global_anavinfo.rc.
To trigger aerosols in the analysis, the table chem_guess needs to include all, or some, of the aerosol fields typically present in the table, but commented out, namely, the five bins of dust (du), five bins of sea-salt (ss), sulfate and organic carbons.
Notice the use of these fields in the analysis is determined by the parameter (number) in the 4-th column of this table. The present default of 11, tells the analysis to use the aerosol fields in the forward model of the radiance assimilation (CRTM). This setting is such that aerosols are not a part of the control vector - this setting is not that which would be needed to get GSI to assimiate aerosol optical depth (for example). The setting for that is different and not a part of the comments in this particular Wiki page.
This aerosol-affected radiance feature is only availabe in recent tags of GEOS-IT (viz., v5.29.4.7) and v5.44.x FP-like systems. In these, aerosol sensitive channels of say, IASI are already triggered (see iaero column of satinfo file). General studies employing this feature will require proper adjustments to IR instruments in satinfo.
The iaero column trigger in satinfo doesn't affect results unless background fields are made available to GSI.
WARNING: At this point (Feb 2026), the user should be aware that only a small subset of all IR has been set to be treated as aerosol-sensitive. So, it is up to the user to be careful to set the iaero paramenters in satinfo for the relevant IR instruments in the experiment period of interest.
Just as a brief illustration of the feature, the table below shows the change in Jo when the IASI instruments available for the GEOS-IT analysis on 12Z 29Mar2010 are similated taking into account their sensitivity to GOCART aerosols (left: control; right: aerosol-affected IASI)
INITIAL Jo:
FINAL Jo:
As closely examined in Kim et al. (2018), GSI tends to accept slightly more observations when the aerosol-affected feature is employed. The effect after multiple cycles is also documented in that work.