Monitoring of Sciamachy Total Column Ozone Using the Dao Ozone Data Asssimilation System

The total column ozone data from SCIAMACHY were monitored in the ozone data assimilation system at NASA’s Data Assimilation office (DAO). The ozone data from NOAA−16 Solar Backscatter UltraViolet/2 (SBUV/2) instrument are assimilated in the DAO’s system. The monitoring consists of computing the differences between SCIAMACHY observations and the ozone system forecast, i.e. observed−minus−forecast (O−F) residuals. The O−F residuals are then analyzed using simple statistical methods. Two monitoring experiments were performed for SCIAMACHY data for the period form October 25 to December 1, 2002. In the first experiment no quality control other than the quality flag provided with the data was used. In the second experiment a simple range check (total column ozone values must be greater that 100 and less than 1000 Dobson units) was used to screen the data before monitoring. In both experiments large O−F residuals were concentrated in the northern and southern high latitudes at what appear to be high solar zenith angles near the terminator. In the experiment with the range check the zonal mean of SCIAMACHY observations is 20 to 30 Dobson units lower that that of the DAO forecast throughout the Tropics and mid−latitudes. At high latitudes where the magnitude of the O−F residuals is particularly large, however, the SCHIAMACHY total ozone is higher then the DAO forecast.