What is IRR?
============

Starting with WRF version 4.0 users may output Integrated Reaction Rate diagnostics
for the MOZART_KPP, or MOZART_MOSAIC_4BIN_KPP, or MOZART_MOSAIC_4BIN_AQ_KPP chemical
schemes.

Integrated Reaction Rate diagnostics are the time integrated value of specified
gas phase reaction rates in one of the above listed chemical schemes.  As an example
suppose that we have the following chemical reaction in the MOZCART chemical scheme:

        k
OH + O3 = HO2

where k is the reaction rate constant.  

To better understand chemical kinetics one often needs to know the value of the expression k * OH * O3

where OH, HO2 are the concentrations of gas phase compounds OH, HO2.

The IRR, Integrated Reaction Rate, enhancement to WRF allows a user to output the time
integrated value of k * A * B at regular time intervals in units of ppmv, parts per million
volumetric mixing ratio.

How do I use IRR?
=================

First, remember that the IRR diagnostics can only be used for chemistry simulations
for the MOZART_KPP, or MOZART_MOSAIC_4BIN_KPP, or MOZART_MOSAIC_4BIN_AQ_KPP chemical
schemes. This means your executable must be compiled with the following environment
variable settings:

setenv WRF_CHEM 1            ( shell = csh, tcsh )
setenv WRF_KPP  1

export WRF_CHEM=1            ( shell = sh,bash,ksh )
export WRF_KPP =1

IRR code is in no way included in non-chemistry WRF executables.

To produce IRR diagnostics one needs:

(1)   the chem namelist group variable irr_opt must be set to 1 on a per simulation
      domain basis; the default value is 0 which produces no IRR diagnostics

(2)   per simulation domain a simple ascii file named wrfchem_irr_diag_d<domain> must exist

For example, suppose you want have a two domain WRF simulation and you want to IRR
diagnostics for the first domain but none for second domain.  You would need to have
the following chem namelist group in the namelist.input file:

&chem
.
.
irr_opt = 1, 0,
.
.
/      

Additionally, if you wanted output for the reaction listed above you would need
to create a file wrfchem_irr_diag_d01 that at the least contained the following line

OH+O3

The wrfchem_irr_diag_d<domain> files are ascii files with one reaction per line.
If there are two reactions with the same reactants, differing products,  then
the second reaction is referenced by appending an _a to the reaction.  Thus if
there were a second reaction, OH + O3 = H + O2 + O2, then this reaction would
be added with the line:

OH+O3_a

in the wrfchem_irr_diag_d<domain> file.

Finally you can include all gas phase reactions in the IRR output by simply
including the line:

all

in the wrfchem_irr_diag_d<domain> file.  The entry "all" may be any mix of lower,upper case.

*** The wrfchem_irr_diag_d<domain> files must be in the simulation run directory. ***

Now you are almost ready to start using the IRR diagnostics.

The IRR diagnostics are bound to the auxhist9 output stream.  As such you need to include
the following time_control group namelist variable settings for a two domain simulation:

auxhist9_outname  = "IRR_DIAG_d<domain>_<date>"
auxhist9_interval = 60, 60
frames_per_auxhist9 = 1, 1
io_form_auxhist9    = 2

You may change the prefix "IRR_DIAG" in the auxhist9_outname to your own preferences.
Similarly the auxhist9_interval, frames_per_auxhist9, and io_form_auxhist9 settings
may be altered.  The above setting will produce IRR output files with the names
IRR_DIAG_d01_<date> and IRR_DIAG_d02_<date> with one time point per file.  The output
files will be produced every 60 simulation minutes and each output file will be netcdf
conforming.

Remember - quick check list
===========================

(1) - set the chem group namelist variable irr_opt to 1 to enable IRR output on a per domain basis
      (irr_opt defaults to 0 => IRR disabled)
(2) - have a wrfchem_irr_diag_d<domain> file in the run directory on a per domain basis
(3) - set the time_control group namelist variables related to auxhist9