An assessment of the accuracy of 14.5 years of Nimbus 7 TOMS Version 7 ozone data by comparison with the Dobson network

A Version 7 algorithm and calibration have been applied to the 14.5 year Nimbus 7 TOMS ozone record (1978-1993). The ozone retrieval algorithm has been significantly improved for cloudy conditions and for high solar zenith angles, and the radiative transfer used in the algorithm is more accurate. New calibration techniques have been used that produce a very stable data set even after 1990 when TOMS degradation became significant. TOMS ozone now agrees with average ozone from an ensemble of 30 northern hemisphere ground stations (Dobsons and Brewers) to within +/-1% throughout most of the 14.5 year record. The time-dependent drift relative to Dobson is 0.29% per decade through the end of the data record. There is almost no solar zenith angle dependence in the comparison for angles below about 80 degrees, but data should be used with caution for larger solar zenith angles. There is also a residual total ozone dependence in the TOMS-Dobson difference, of about 1% per 100 DU.