An analysis of the 7‐year record of SBUV satellite ozone data: Global profile features and trends in total ozone

Abstract

An analysis of Nimbus 7 solar backscattered ultraviolet (SBUV) monthly average total ozone data for changes over the 7‐year period from November 1978 through September 1985 is considered. Regression‐time series models, which include seasonal components, a linear trend term, an F10.7 solar flux term, and an autocorrelated autoregressive noise term to account for variations in total ozone, are estimated for both latitudinal zonal averages and a global series over this time period. The resulting linear trend and solar flux coefficient estimates are examined. A comparison between SBUV monthly average total ozone data near Dobson ground station locations and the corresponding Dobson station total ozone data is performed for a network of 35 Dobson stations. Linear drifts are estimated for the differences between SBUV and Dobson total ozone data at each station. The results show an average negative linear drift in SBUV data relative to Dobson data of about −0.4% per year. A linear trend estimate for the global SBUV series of (−0.74±0.26)% per year is obtained for the model which takes into account the association of ozone changes with solar flux variations. When this linear trend estimate for the global SBUV series is “corrected” for the negative drift between SBUV and Dobson data, the 95% confidence interval estimate of the linear trend component in the global SBUV series, exclusive of trend variations associated with solar flux variations, over this 7‐year period is (−0.35±0.28)% per year. The global estimate of the relation between total ozone and solar flux variations is (0.97±0.61)% per 100 solar flux units, which represents a change in total ozone over this 7‐year period associated with solar flux variations of about (−0.20±0.13)% per year. Comparisons are also performed which indicate that trends obtained from SBUV data at the Dobson station network of locations over this 7‐year period are quite similar to trend estimates obtained from the global SBUV series. When comparing the above SBUV data global trend estimate for the 7‐year period with a linear trend estimate of (−0.04±0.07)% per year obtained from a network of Dobson station data over the longer period 1970–1985, we find that the trend estimate for the recent 7‐year period is considerably more negative but with a much larger standard error. In recognition of the rather unusual natural atmospheric fluctuations which occurred during the period 1982–1985, no firm conclusions can be drawn in terms of interpretation of the negative trend finding over the relatively short 7‐year time period. Such interpretations require a detailed understanding of the atmospheric dynamical and chemical mechanisms related to ozone variations during this period.