Comparisons of OMI total ozone with SBUV/2 and NCEP GFS assimilations

The NCEP Global Forecast System (GFS) currently assimilates ozone from SBUV/2 onboard NOAA-16 satellite. We plan to improve the assimilation in the future by incorporating AURA ozone measurements including OMI and HIRDLS. As a first step total ozone measurements from the AURA OMI instruments are compared with those from NOAA-16 and -17 SBUV/2 and the current GFS assimilations. Two different methods are used for the comparison. One is comparing those matching points of direct observations of OMI and SBUV/2 with the matching window set to within 0.5 degree of latitude/longitude and within 5 minutes of observation time. Another is comparing daily mapped OMI ozone data and the 12Z ozone assimilations of the NCEP GFS, with the map resolution of 1 degree of latitude/longitude. Preliminary results show some encouraging features such as that OMI catches finer structure of small scale than NCEP GFS assimilations which use SBUV/2, and that the OMI and GFS ozone are in good agreement between 60S and 65N, with zonal average difference less than 5 DU. The stage-1 validated OMI total ozone data are expected for public release in April 2005. The data then will be compared with SBUV/2 version 8 total ozone (which has a very similar algorithm to the OMI product) and the NCEP GFS assimilations.