Glow.txt

                  Preliminary Documentation for the GLOW Model
    
                               Version 0.981

               ***  see Releasenotes.txt for release notes  ***
  
                           Stan Solomon, 3/2017
  
   The GLobal airglOW (GLOW) model is a family of subroutines that calculates
ionization and excitation rates, energetic electron production and transport,
excited species densities, and airglow emission rates for the terrestrial
thermosphere.  Use is governed by the Open Source Academic Research License
Agreement contained in the file Glowlicense.txt.  Standards and practices are
specified by the "rules of the road" adopted by the CEDAR and TIMED programs.  
   Other than the example driver programs, the input files, Makefile, run
script, and possibly the master subroutine glow.f90, it is inadvisable to modify
the code.  If any changes are required, please suggest them to:
  
   Stan Solomon, HAO/NCAR, Boulder, CO 80301
   Phone: 303-497-2179
   Email: stans@ucar.edu
  
   Since this is a developmental code, there are bound to be problems which
users will uncover.  Please let me know about them.  I will also attempt to
accommodate any reasonable suggestions for enhancements or changes.  By
following this procedure, users will benefit by staying compatible with future
developments, and from a more systematic elimination of any progrmming errors.
Also, please upgrade to the latest version.  Use of obsolete versions may lead
to incorrect results.

   The main inputs to GLOW are: neutral thermopshere major species density
(O, O2, N2), minor species NO and N(4S), the electron density, the neutral,
ion, and electron temperatures, all on a 1D altitude grid, for specified
time and geographic coordinates.  Solar flux, and auroral electron flux, are
specified or calculated from parameters.  Outputs include electron density
calculated below 200 km, ionized and excited species density, airglow volume
emisison rates, and vertical column brightnesses.  Various parameters used
to calculate these are also available on output.  GLOW does not perform any
transport calculations, so above 200 km, the electron density must be
specified, since photochemical equilibrium is only valid to ~200 km altitude.
There are several other options for specifying ionospheric parameters.  GLOW
calculates dissociation rates, and will return N(2D), O(1D), etc., but not
N(4S), NO, or O(3P), since they are subject to transport.
  
   Program glowbasic.f90 is provided to give some guidance in using
the subroutine package, one profile at a time, similar to previous versions.
It uses NRLMSISE-00 and IRI-90 to specify the neutral atmosphere and
initial electron density profile, and the NOEM model to specify nitric oxide
density.  This program is intended as an example to be modified by the user
to suit particular purposes.  It is not necessary to use MSIS, IRI, and NOEM;
any model or measurement that specifies neutral densities, temperatures, and
high-altitude electron densities can be employed.  The output statements at the
end are just examples of a small subset of the calculated parameters.
To get started with glowbasic:
   cp Makefile.glowbasic Makefile
   gmake
   glow.exe < in.basic.day > test.basic.day
You don't need to use the Makefile or the input files, you can compile and
link manually, and run with command-line input.
You can also run glowbasic out of IDL using:
   spawn, '.glow.exe < input.file > output.file'

   Program glowdriver.f90 is a parallel processing program set up to use output
from general circulation models such as the NCAR TIE-GCM and TIME-GCM to
specify the neutral densities, electron density, and temperatures, and then
calculate airglow emissions globally on the GCM grid.  It uses
netCDF files for input and output, and a namelist input file to specify input
options.
   To run GLOW with TIE-GCM or TIME-GCM inputs, the GCM is run first, and a
secondary history file created.  This file must contain the output fields:
Zg, Te, Ti, Te, Ne, O2, O1, N2, NO, N4S, N2D,
and optionally the auroral parameters:
eflux, nflux, alfa, cusp, drizzle, ec, alfac, ed.
He, un, and vn anre also optional, which are not used by GLOW, but are passed
through to the output files. 

   Program glowdriver.f90 can also be run globally using MSIS/IRI
inputs.  Solar and auroral parameters are taken from the GCM histories when
running in GCM mode, and can be supplied by the user when in empirical mode,
although there is no way to provide auroral spatial distributions when running
in empirical mode at this time, so these would generally be omitted.
To use glowdriver:
   cp Makefile.glowdriver Makefile
   gmake
   runglow.job
You don't need to use the runglow.job script, you can use mpirun from the
command line.  The script is set up to use 6 processors, input from the
file in.namelist, netCDF output to a file specified by the namelist inputs,
and log messages to the file out.log.  The script can easily be edited to
change these.
  
   Subroutine GLOW is the master routine of the package.  It receives input
parameters from the calling program use associated through module CGLOW, calls
the other subroutines, and returns results through use associatedvariables.  Iti
is not necessary to use subroutine GLOW to call the others - those particularly
bold and well-informed users who desire to use some subset of the package
may attempt to do so, using subroutine GLOW as guidance. 

   The data files ephoto_x*.dat, ssflux_*.dat, and snoem_eof.dat are provided in
subdirectory data/ of the working directory.  Parameter files for IRI-90 are
provided in data/iri90/.  These files can put put in any directory as long as
their paths are correctly specified in the driver program or its namelist
inputs.  The number of wavelenth bins in the ephoto and ssflux files must equal
the parameter LMAX specified in module CGLOW, and the wavelength ranges must be
the same in all input files.
  
   These routines are written in standard Fortran-90 and MPI, and should be
compatible with most compilers.  However, their performace has only been tested
using the Intel ifort compiler with -O3 optimization running under CentOS Linux
on 64-bit machines.  The Portland Group compiler should also work but I haven't
been using it lately since ifort is faster.  I would be interested in hearing
of experiences with other compilers and/or operating systems, but make no claims
or promises.  To use with the glowdriver program, MPI and netCDF libraries must
be installed.  However, glowbasic shouldn't require anything other than Fortran.
  
Subroutines called by the example programs include:
  MPI*       Message-passing interface utilities
  CGLOW_INIT Initializes array dimensions and shared variables in module CGLOW
               (This takes the place of common blocks previously employed)
  EGRID      sets up electron energy grid   
  READ_TGCM  Reads GCM model history files and returns fields on GCM grid
  TZGRID     Interpolates GCM fields onto H/4 altitude grid
  MZGRID     Returns empirical model quantities on a default altitude grid
  GTD7       NRL Mass Spectrometer Incoherent Scatter - 00 (NRLMSISE-00) model
               (Picone et al., 2002)
  TSELEC     Set-up entry for MSIS-00
  IRI90      International Reference Ionosphere-1990 (IRI-90) model
              (Belitza, 1990)
              (Note: a special modification of the original code is provided.)
  SNOEMINT   Interpolates NO output onto model grid
  SNOEM      Implementation of Nitric Oxide Empirical Model (NOEM)i
               (Marsh et al., 2005)
  GEOMAG     Translates geographic to geomagnetic coordinates and vice versa
  MAXT       Generates a Maxwellian electron spectrum
  GLOW       Master subroutine of the GLOW package
  CONDUCT    Calculates ionospheric Hall and Pederson conductivities
               (McGranaghan et al., 2016)
  OUTPUT     Writes global netCDF output files, similar to GCM histories
  
Subroutines called by GLOW are:
  FIELDM  calculates magnetic dip angle
  SOLZEN  calculates solar zenith angle
  SSFLUX  scales solar flux for activity level
  RCOLUM  calculates slant column density of major species
  EPHOTO  calculates photoionization and photoelectron production
  QBACK   estimates background ionization
  ETRANS  computes electron transport, ionization, excitation using
            Nagy & Banks 2-stream method
            calls EXSECT for cross-sections, first call only
  GCHEM   finds electron/ion/metastable densities, airglow emissions
  BANDS   calculates band-specific airglow emission rates (currently only LBH)
  
Definitions:
  
! Array dimensions:
! JMAX    number of altitude levels
! NBINS   number of energetic electron energy bins
! LMAX    number of wavelength intervals for solar flux
! NMAJ    number of major species
! NST     number of states produced by photoionization/dissociation
! NEI     number of states produced by electron impact
! NEX     number of ionized/excited species
! NW      number of airglow emission wavelengths
! NC      number of component terms for each emission
  
! Supplied to subroutine using use-associated data defined in module CGLOW:
! IDATE   Date, in form yyddd
! UT      Universal Time; seconds
! GLAT    Geographic latitude; degrees
! GLONG   Geographic longitude; degrees
! ISCALE  Solar flux scaling switch, see subroutine SSFLUX
! JLOCAL  =0 for electron transport calculation, =1 for local calc only
! KCHEM   Ion/electron chemistry switch, see subroutine GCHEM
! F107    Solar 10.7 cm flux for day being modeled, 1.E-22 W m-2 Hz-1
! F107A   Solar 10.7 cm flux 81-day centered average
! XUVFAC  Factor by which to multiply to solar flux 16-250 A or 16-50 A.
! ZZ      altitude array; cm
! ZO      O number density at each altitude; cm-3
! ZN2     N2  "      "      "   "     "       "
! ZO2     O2         "
! ZNO     NO         "
! ZNS     N(4S)      "
! ZND     N(2D)      "
! ZRHO    mass density at each altitude; gm cm-3 (not currently in use)
! ZE      electron density at each alt; cm-3
! ZTN     neutral temperature at each alt; K
! ZTI     ion temperature at each alt; K
! ZTE     electron temp at each alt; K
! PHITOP  energetic electron flux into top of atmosphere; cm-2 s-1 eV-1

! Calculated by subroutine and returned in variables  defined in module CGLOW:
! SZA     solar zenith angle; radians
! DIP     magnetic field dip angle; radians
! EFRAC   energy conservation check from ETRANS, (out-in)/in
! IERR    error code returned from ETRANS:
!           0=normal, 1=local problem, 2=transport problem
! ZMAJ    major species density array, O, O2, N2; cm-3
! ZCOL    major species slant column density array, O, O2, N2; cm-2
! WAVE1   longwave edge of solar flux wavelength range; A
! WAVE2   shortwave edge of solar flux wavelength range; A
! SFLUX   scaled solar flux in each wavelength range; photons cm-2 s-1
! ENER    electron energy grid; eV
! DEL     width of each bin in electron energy grid; eV
! PESPEC  photoelectron production rate at energy, altitude; cm-3 s-1
! PIA     proton aurora ionization rate (not currently in use); cm-3 s-1.
! SESPEC  proton aurora secondary electron production rate (not currently in use); cm-3 s-1
! PHOTOI  photoionization rates for state, species, altitude; cm-3 s-1
!           O+ states: 4S, 2Do, 2Po, 4Pe, 2Pe
!           O2+ states: X, a+A, b, dissoc.
!           N2+ states: X, A, B, C, F, dissoc.
! PHOTOD  photodissoc. & exc. rates for state, species, alt.; cm-3 s-1
!           (1,2,J) = O2 -> O(3P) + O(1D))
!           (2,2,J) = O2 -> O(3P) + O(1S)
!           (1,3,J) = N2 -> N + N
! PHONO   photoionization/dissociation/excitation rates for NO, cm-3 s-1
!         (1,J) = NO+ from H Ly-a ionization
! SION    electron impact ionization rates calculated by ETRANS; cm-3 s-1
! UFLX    upward hemispherical electron flux; cm-2 s-1 eV-1
! DFLX    downward hemispherical electron flux; cm-2 s-1 eV-1
! AGLW    Electron impact exc. rates; state, species, alt.; cm-3 s-1
!           O states: 1D, 1S, 5S, 3S, 3p5P, 3p3P, 3d3D, 3s'3D
!           O2 states: a, b, (A+A'+c), B(SRC), 9.9eV, Ryds., vib.
!           N2 states: (A+B+W), B', C, (a+a'+w), 1Pu, b', Ryds., vib.
! EHEAT   ambient electron heating rate, eV cm-3 s-1
! TEZ     total energetic electron energy deposition, eV cm-3 s-1
! TPI     total photoionization rate at each altitude, cm-3 s-1
! TEI     total electron impact ionization rate at each altitude, cm-3 s-1
! TIR     total ionization rate at each altitude (TPI+TEI), cm-3 s-1
! ECALC   electron density, calculated below 200 km, a priori above; cm-3
! ZXDEN   array of ionized/excited state densities at each altitude; cm-3:
!           O+(2P), O+(2D), O+(4S), N+, N2+, O2+, NO+, N2(A), N(2P),
!           N(2D), O(1S), O(1D); cm-3
! ZETA    array of volume emission rates at each altitude; cm-3 s-1:
!           3371A, 4278A, 5200A, 5577A, 6300A, 7320A, 10400A, 3466A,
!           7774A, 8446A, 3726A, LBH, 1356, 1493, 1304; cm-3 s-1
! VCB     array of vertical column brightnesses (as above); Rayleighs
! ZCETA   array of contributions to each v.e.r at each alt; cm-3 s-1:
! ZCETA(*,1,z): N2(C) 2nd positive (0,0) band at 3371A:
!   1: electron impact excitation N2 + e* -> N2(C)
!   2: underlying N2(A) VK (0,9) band
! ZCETA(*,2,z): N2+(B) 1st positive (0,1) band at 4278A:
!   1: electron impact ionizing excitation N2 + e* -> N2+(B)
!   2: photoionizing excitation N2 + hv -> N2+(B)
!   3: resonant fluroescence N2+ + hv -> N2+(B)
! ZCETA(*,3,z): N(2D) line at 5200A:
!   1: photodissociation N2 + hv -> N + N(2D)
!   2: photodissociative ionization N2 + hv -> N+ + N(2D)
!   3: electron imact dissociation N2 + e* -> N + N(2D)
!   4: electron impact dissociative ionization N2 + e* -> N+ + N(2D)
!   5: dissociative recombination NO+ + e -> N + N(2D)
!   6: dissociative recombination N2+ + e -> N + N(2D)
!   7: atom-ion interchange N2+ + O -> NO+ + N(2D)
!   8: quenching N(2P) + O -> N(2D) + O
!   9: radiational cascade N(2P) -> N(2D) + hv
! ZCETA(*,4,z): O(1S) "green" line at 5577A:
!   1: electron impact excitation O + e* -> O(1S)
!   2: dissociative recombination O2+ + e -> O + O(1S)
!   3: energy transfer N2(A) + O -> N2 + O(1S)
!   4: atom-ion interchange O2+ + N -> NO+ + O(1S)
!   5: chemiluminescence N(2D) + NO -> N2 + O(1S)
!   6: photodissociation O2 + hv -> O + O(1S)
! ZCETA(*,5,z): O(1D) "red" line at 6300A:
!   1: electron impact excitation O + e* -> O(1D) 
!   2: thermal electron excitation O + e -> O(1D)
!   3: dissociative recombination O2+ + e -> O + O(1D)
!   4: chemiluminescence N(2D) + O2 -> NO + O(1D)
!   5: energy transfer N(2D) + O -> N + O(1D)
!   6: atom-ion interchange N+ + O2 -> NO+ + O(1D)
!   7: energy transfer O+(2D) + O -> O+ + O(1D)
!   8: electron impact dissociation O2 + e* -> O + O(1D)
!   9: photodissociation O2 + hv -> O + O(1D)
!  10: radiative cascade O(1S) -> O(1D) + hv
! ZCETA(*,6,z): O+(2P) line at 7320A:
!   1: photoionization O + hv -> O+(2P)
!   2: photodissociative ionization O2 + hv -> O + O+(2P)
!   3: electron impact ionization O + e* -> O+(2P)
!   4: electron impact dissociative ionization O2 + e* -> O + O+(2P)
! ZCETA(*,7,z): N(2P) line at 10400A:
!   1: photodissociation N2 + hv -> N + N(2P)
!   2: photodissociative ionization N2 + hv -> N+ + N(2P)
!   3: electron imact dissociation N2 + e* -> N + N(2P)
!   4: dissociative recombination N2+ + e -> N + N(2P)
! ZCETA(*,8,z): N(2P) line at 3644A:
!   1: photodissociation N2 + hv -> N + N(2P)
!   2: photodissociative ionization N2 + hv -> N+ + N(2P)
!   3: electron imact dissociation N2 + e* -> N + N(2P)
!   4: dissociative recombination N2+ + e -> N + N(2P)
! ZCETA(*,9,z): O(3p5P) line at 7774A:
!   1: electron impact excitation O + e* -> O(3p5P)
!   2: radiative recombination O+ + e -> O(3p5P)
!   3: mutual neutralization O+ + O- -> O(3p5P)
! ZCETA(*,10,z): O(3p3P) line at 8446A:
!   1: electron impact excitation O + e* -> O(3p3P)
!   2: electron impact excitation and cascade O + e* -> O(3d3D) -> O(3p3P)
!   3: electron impact excitation and cascade O + e* -> O(3s'3D) -> O(3s3P)
! ZCETA(*,11,z): O+(2D) line at 3726A:
!   1: photoionization O + hv -> O+(2D)
!   2: photodissociative ionization O2 + hv -> O + O+(2D)
!   3: electron impact ionization O + e* -> O+(2D)
!   4: electron impact dissociative ionization O2 + e* -> O + O+(2D)
!   5: quenching O+(2P) + e -> O+(2D) + e
!   6: radiational cascade O+(2P) -> O+(2D) + hv
! ZCETA(*,12,z): N2(a) LBH total band system
!   1: electron impact excitation N2 + e* -> N2(a)
! ZCETA(*,13,z): O(3s5S) doublet at 1356A
!   1: electron impact excitation O + e* -> O(3s5S)
!   2: electron impact excitation and cascade O + e* -> O(3p5P) -> O(3s5S)
!   3: radiative recombination O+ + e -> O(3s5S)
!   4: mutual neutralization O+ + O- -> O + O(3s5S)
! ZCETA(*,14,z): N(3s2P) doublet at 1493A
!   1: photodissociation N2 + hv -> N + N(3s2P)
!   2: electron impact dissociation N2 + e* -> N + N(3s2P)
! ZCETA(*,15,z): O(3s3S) triplet at 1304A
!   1: electron impact excitation O + e* -> O(3s3S)
!   2: electron impact excitation and cascade O + e* -> O(3p3P) -> O(3s5S)
!   3: electron impact excitation and cascade O + e* -> O(3d3D) -> -> O(3s5S)
!   4: electron impact excitation and cascade O + e* -> O(3s'3D) -> -> O(3s5S)
!   5: radiative recombination O+ + e -> O(3s3S)

A few notes:

   With version 0.98, GLOW now uses Fortran 90 conventions, including
use-associated variables defined in module CGLOW instead of in common blocks.
This was done for compatibility with parallel processing using MPI.  Most of the
routines were re-cast in free-form style, largely changed to lower case, and
have a ".f90" file extension suffix.  I am using a terminal column-width of 
100 characters for editing and 132 characters for tabular output.  There are
some routines still coded in fixed-format Fortan-77 style, including
exsect.f and fieldm.f.  The reason for this is that these two are due for an
overhaul and replacement, respectively, and it didn't seem worthwhile to
re-format them at this time.  (Subroutine exsect will ultimately be changed to
tablular data-file inputs instead of analytic functions, and fieldm will be
updated to IGRF/Apex coordinates).

   The parallel processing strategy adopted is to let main program
glowdriver.f90 handle all MPI calls, so that the core subroutines can be used
in either multiple or single-processor mode.  The 0th task performs all
I/O and empirical model calls, distributes variables to the other tasks,
collects the results, and outputs them to a netCDF file.  The domain
decomposition is one-dimensional in latitude.  The number of tasks (processors)
must be an integral multiple of the number of latitudes.  Since a typical 5x5
degree grid has 36 latitudes, 4, 6 or 12 processors are good numbers to use.
Note that on the new NCAR Cheyenne supercomputer, one node has 36 cores!
The number of processors is configurable in the job script runglow.job.

   Versions of NRLMSISE-00 and IRI-90 are provided for the convenience of users
who do not have their own copies.  Attribution to the appropriate sources
(Picone et al, 2002; Belitza, 1990) should be made.  The version of IRI
provided is not the standard version, as I have modified it to work on various
systems, particularly volatile memory systems.  However, I cannot guarantee
that the results obtained from them are correct.  Caution: IRI occasionally
writes messages on unit 12.  IRI data files ccir*.asc and ursi*.asc
are contained in ./data/iri90/ and this directory or a different directory
can be specified in the namelist inputs.  MSIS and IRI are old-style Fortran
with common blocks, and hence are not appropriate for MPI implementation, so
they are called by glowdriver using the 0th processor only.  Since they are
very fast (compared to, e.g., etrans) this is a minimal performance loss.

   When using GCM inputs, note that the TIE-GCM altitude grid doesn't extend
below ~97 km, but electron transport calculations require a "sponge" layer, so
densities are extrapolated from ~79 km to ~97 km using an assumed constant scale
height of 6 km.  Temperatures, Electron density, and nitric oxide density are
assumed to be constant below the bottom of the grid.  Therefore, results below
~97 km should be ignored.  This is not a problem for the TIME-GCM since its
altitude grid extends down to ~30 km, but note that GLOW does not yet contain
full D-region chemistry or mesopause-region recombination emissions.  For
empirical model inputs, MSIS and IRI provide full altitude profiles, but NOEM
only extends from 100-150 km, so a constant value is used for nitric oxide
below 100 km, and a scale height assumption above 150 km.

   For TIE- or TIME-GCM runs that will be used for input to GLOW, secondary
history files should be employed.  It is possible to use primary histories
but not recommended, since no auroral parameters will be included.  The
following secondary history output fields should be specified: ZG, TN, TI, TE,
NE, O1, O2, N2, NO, N4S, N2D, HE, UN, VN, EFLUX, NFLUX, ALFA, CUSP, DRIZZLE.
Note that HE, UN, and VN are not used, but are passed through to
output.  The auroral parameters EFLUX, NFLUX, ALFA, CUSP, and DRIZZLE are
optional but should be included.  (CUSP and DRIZZLE are not yet used,
but may be soon.)  If ZG or N2 are ommitted, they will be calculated by
readtgcm, provided that HE is included.

   The default energy grid extends to 50 keV and is appropriate for most
photoelectron and auroral calculations; the electron energy grid can extend
(in principle) to 1 GeV.  The altitude grid may be altered to suit the user's
needs, but with caution.  The two biggest pitfalls are not providing enough
resolution and not providing a deep enough atmosphere.  There should be no
significant flux of electrons out of the bottom of the altitude grid.  As for
resolution, a rule of thumb is about four points per scale height. 

   The ETRANS error code IERR and energy conservation ratio EFRAC
should be checked for normal return.  IERR should equal zero; if it doesn't
it means that the total inelastic cross section is near zero somewhere, which
is usually caused by a near zero ambient electron density.  EFRAC should be
less than ~0.03 for photoelectron calculations, and less than ~0.1 for aurora.
It can get up to the 0.1-0.2 range in the twilight, which is not good, but at
present unavoidable.
  
   Electron density calculations can be made by GCHEM below 200 km but not
above where transport/diffusion effects become important.  Therefore, an
electron density profile (such as from the NCAR TIE-GCM or from IRI) must be
provided above 200 km.  An initial non-zero electron density profile must be
provided at all altitudes in array ZE because otherwise ETRANS will produce
an error.  Calculated electron densities are returned in array ECALC, with
values from ZE included where calculations are not made.  The switch KCHEM
determines what ion/electron density calculations are made (see subroutine
GCHEM).  With the exception of KCHEM=0 (no calculations), none are foolproof.
One irritation that may be noted when KCHEM=4 (calculate Ne below 200 but use
provided Ne above 200) is a discontinuity in Ne(z) at 200 km.  GCHEM attempts
to deal with this by interpolating from the 200 km level to three grid
points above it.  Another caveat with KCHEM=4 or KCHEM=3 (Ne provided,
ions calculated) is that if there is an incompatibility between the specifed
Ne(z) and the calculated ionization rates, negative values for some ions may
result.  KCHEM=2 (electrons and major ions provided, minor ions calculated) and
KCHEM=1 (electrons and all ions except O+(2D,2P) provided) should be fairly
reliable.

   For daytime calculations, the parameter XUVFAC is provided to deal with the
uncertainty concerning the solar spectrum from 18-250 A.  When the
Hinteregger et al. [1981] model is employed, a reasonable value for XUVFAC is
2.0, as suggested by Richards et al. [1984; 1994], however a value as high as
4.0 might be realistic, as discussed by Solomon et al. [2001].  When the
EUVAC model [Richards et al., 1994] is employed, XUVFAC is only applied
to the region still obtained from the Hinteregger model, 18-50 A, since
longward of that point EUVAC has already increased the solar fluxes relative
to the Hinteregger spectrum (by factors of 2-3).  SSFLUX also now provides
the ability for the user to specify a solar spectrum from other models or
measurements, in which case XUVFAC is ignored.  The number of bins in the
solar spectrum input file must be equal to LMAX (specified in glow.h) and
the wavelength ranges must correspond to those in ephoto_x*.dat.

   The upper boundary of the electron transport calculation by ETRANS is
specified by the PHITOP array, which may contain a flux of auroral electrons,
conjugate photoelectrons, or both.  The initial electron density profile
input for the call to GLOW can be replaced by the calculated profile below
200 km, and GLOW called again.  This isn't really necessary, but gives an
improved estimate of the low-energy electron flux (which depends on the ambient
electron density), since IRI isn't really valid in the auroral regions.
For high-energy calculations this second call may safely be skipped.

   The example programs use the NOEM model of nitric oxide, based on data from
the SNOE satellite, as an empirical input [Marsh et al., 2004].  When running
from GCM fields the NO calculated by the GCM is used.
  
   Electron impact cross sections generated by EXSECT can be obtained from
variables use associated through the CGLOW module.

   A note on units:  GLOW uses cgs in its internal calculations.  Wavelengths
are described in nanometers in this publication, but Angstroms are used for 
solar and airglow emission wavelengths inside the code.  Energies are in 
electron volts (eV), except for the input auroral total energy flux, which is 
expressed in erg cm-2 (equivalent to mW m-2).  Other units employed for 
convenience are megabarns (10-18 cm2) and Rayleighs (106 photons cm-2).  
Conductivities are output in Siemens/meter (mhos).  Kilometers are used in 
driver program altitude grids, but are converted to centimeters internally.  
Dates are in yyyyddd or optionally yyddd format, universal time 
is in seconds, and local solar time is in hours.  The solar radio 
flux index F10.7 is in expressed in units of 10-22 W m-2. 

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   J. Geophys. Res., 75, 6260, 1970.
Solomon, S. C., P. B. Hays, and V. J. Abreu, The auroral 6300A emission:
   Observations and modeling, J. Geophys. Res., 93, 9867, 1988.
Solomon, S. C., and V. J. Abreu, The 630 nm dayglow, J. Geophys. Res., 94,
   6817, 1989.
Solomon, S. C., Auroral particle transport using Monte Carlo and hybrid
   methods, J. Geophys. Res., 106, 107, 2001.
Solomon, S. C., S. M. Bailey, and T. N. Woods, Effect of solar soft X-rays
   on the lower atmosphere, Geophys. Res. Lett., 28, 2149, 2001.
Bailey, S. M., C. A. Barth, and S. C. Solomon, A model of nitric oxide in the
   lower thermosphere, J. Geophys. Res., 107, 1205, 2002.
Solomon, S. C., Global modeling of thermospheric airglow in the
   far-ultraviolet, J. Geophys. Res., submitted, 2017.