TROPOSPHERIC OZONE DATA FROM AURA OMI/MLS
The OMI Level-2 footprint measurements have a "row anomaly" problem
(beginning in late June 2007) which has been corrected for. The row
anomaly problem became very bad in late January 2009 with about 1/3 of
OMI's 60 rows greatly affected. Note that the first three lines in
the ASCII files below provide information about the data. In effort
to provide data values to three significant digits in these ASCII
files, tropospheric column ozone (in Dobson Units) was multiplied by
10 and mean volume mixing ratio (in ppbv) was multiplied by 5. -
J. R. Ziemke
MONTHLY-MEAN TROPOSPHERIC COLUMN OZONE (IN DOBSON UNITS X 10):
Here is an IDL reader
for the above ASCII data files
NOTES FOR ALL MONTHLY MEAN DATA: OMI/MLS tropospheric ozone was
first determined daily by subtracting co-located MLS stratospheric
column ozone from OMI total column ozone each day. Stratospheric
column ozone from MLS was spatially interpolated (2D Gaussian/linear
latitude-longitude interpolation) each day to fill in between the
actual along-track measurements. Monthly mean fields were then
determined by averaging all available daily data within each month.
OMI total column ozone was filtered for near clear-sky conditions by
including only measurements when coincident OMI reflectivity was less
than 0.3. Further details for the OMI/MLS method are discussed by
Ziemke et al.  (PDF
file, 5.0 Mb)
The tropospheric ozone measurements use National Centers for
Environmental Prediction (NCEP) analyses and World Meteorological
Organization (WMO) 2K per km vertical temperature gradient definition
to determine tropopause pressure. All data correspond to ascending
(south to north) daytime Aura orbits where MLS makes a limb profile
measurement in the direction of the Aura spacecraft orbital motion
about 7 minutes prior to the total ozone measurement from OMI. The
data are gridded to 288 longitude grid points with central longitudes
-179.375, -178.125, -176.875, …., 178.125, 179.375, and 120 latitude
gridpoints with central latitudes -59.5, -58.5, -57.5, …, 58.5, 59.5.
The first three lines of each data file is preamble text describing
the data file, and is followed by the actual data beginning with
latitude -59.5. IMPORTANT: All ASCII data files were scaled to
maximize information content to three numeric characters per value.
Tropospheric column ozone (TCO, in Dobson Units) was multiplied by 10.
Any missing data is listed as "999" in the data files.