OMI Solar Spectral Irradiance Data
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Authors:  Sergey Marchenko and Matthew DeLand

Contact:  sergey.marchenko@ssaihq.com

Last revision:  25 November 2019


Data Product
************

This file gives a basic description of the solar spectral irradiance data that 
we have produced from Aura OMI solar measurements.  Detailed discussion of the 
procedures used and validation steps can be found in the following papers:

S. V. Marchenko and M. T. DeLand (2014), "Solar spectral irradiance changes 
  during Cycle 24", Ap. J. 789:117, doi:10.1088/0004-637X/789/2/117.

S. V. Marchenko, M. T. DeLand, and J. L. Lean (2016), "Solar spectral irradiance 
  variability in Cycle 24:  Observations and models", J. Space Weather Space 
  Climate, 6, A40, doi:10.1051/swsc/2016036.

S. V. Marchenko, T. N. Woods, M. T. DeLand, S. Mauceri, P. Pilewskie, and M. 
  Haberreiter (2019), Improved Aura/OMI solar spectral irradiances: Comparisons
  with independent data sets and model predictions, Earth and Space Sci., in 
  press, doi:10.1029/2019EA000624.

Please note that this data set has been revised in three areas, as described in
our 2019 paper:

   1. We have improved the separation of pixels flagged as noise-affected, which
      provides more data in the later part of the OMI record.
   2. We now use an exponential time dependence for our degradation model, 
      replacing the previous linear function.
   3. We now require consistent absolute irradiance levels at the minimum of 
      Cycle 23 and Cycle 24 as a constraint for item (2).

Since Cycle 24 may not have reached its full minimum yet, we believe that 
item (3) currently leads to an underestimate of ~0.1% for solar cycle 
variability in the UV region (wv < 350 nm), and < 0.05% in the visible region.

The revised degradation model now enables us to extrapolate the correction function 
back to July 2006.


Data Location
*************

The OMI data can be retrieved at the following web site:

   https://sbuv2.gsfc.nasa.gov/solar/omi/


File Contents
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The OMI irradiance data, corrected for long-term degradation, are provided in a 
single IDL save set named 'corrected_solar_flux_regular_diff_nov_2019.sav'.  All  
data are provided separately for each of three spectral channels, where the term 
'CHN' in the variable name has the following definitions:

   'uv1'  =  UV1 channel, wavelength range = 265.0-309.5 nm
   'uv2'  =  UV2 channel, wavelength range = 310.0-355.5 nm
   'vis'  =  VIS channel, wavelength range = 356.0-500.0 nm

The save set contains the following variables, where 'CHN' is defined as above 
for each channel:

   JUL_DATE          Observation date in adjusted Julian day format 
                       [JD-2450000.0]
   chn_REFERENCE     Reference irradiance spectrum created by averaging data 
                       between April 2007 and September 2009 
                       [photons/cm^2/sec/nm]
   chn_BIN           Daily spectra, expressed as normalized irradiance relative 
                       to the reference spectrum irradiance value at each 
                       wavelength
   chn_BIN_STD       Normalized standard deviation within each spectral and 
                       daily bin
   LA_chn            Wavelength scale [nm], sample interval = 0.5 nm

For users who prefer to use data in HDF format, the file 
'omi_ssi_update_20191125.h5' is also available.  It contains the same 
information as the IDL save set, with the following mapping of variables:

   JUL_DATE       -->  JulianDateAdj
   chn_REFERENCE  -->  IrradianceReference{chn}
   chn_BIN        -->  IrradianceNormalized{chn}
   chn_BIN_STD    -->  IrradianceStDev{chn}
   LA_chn         -->  Wavelength{chn}

The first measurement date available in the OMI data product is 2 July 2006, 
and the last date included in the current data file is 22 November 2019.