Effect of an improved cloud climatology on the total ozone mapping spectrometer total ozone retrieval

The 14.5 years of Nimbus 7 total ozone mapping spectrometer (TOMS) gridded data have been reprocessed using the Version 7 (V7) algorithm. Among a number of improvements made in the TOMS V7 algorithm, a new cloud top height climatology, based upon the International Satellite Cloud Climatology Project (ISCCP) data set, has been included to correct for the cloud height effect on total ozone. The new algorithm also contained an improved cloud model that used a modified Lambertian surface assumption in the partially clouded scenes. As a result, reductions in TOMS V7 total ozone, as compared to Version 6 data, could be more than 20 Dobson units over marine stratocumulus, while in high cloud regions the V7 measured total ozone amounts are generally higher than V6 values. The high correlation between TOMS V6 total ozone and reflectivity has been greatly reduced using the V7 data, particularly in the low cloud region of the tropical eastern Atlantic. Also, the land-ocean contrast in total ozone associated with the inadequate cloud height climatology and partial cloud model has diminished in the V7 data. The land-ocean contrast in total ozone due to the sensitivity of the lower tropospheric ozone to ground reflectivity, however, still remains.