Total ozone seasonal and interannual variations derived from the 7 year Nimbus‐4 BUV data set

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Abstract
Backscattered ultraviolet (BUV) data from the Nimbus‐4 spacecraft for the period 1970–1977 have been recently processed to final form. This paper is based upon an analysis of all the total ozone data available in the 7‐year data set. The seasonal and interannual variations of total ozone over the globe are examined, using daily zonal means of 10° latitude bands and a time latitude cross section. A harmonic analysis was performed on the daily zonal means, and the amplitude, phase, and percentage of variance were computed for the annual, semiannual, and higher harmonics for several years and for individual years. Many of the features observed earlier for the period 1970–1972, such as the asymmetry of the annual wave in the two hemispheres, persist over the longer data period. Variations with regular periods shorter than a few months were sought, but none were evident systematically throughout the latitude zones. Examination of the zonal mean data with the mean annual wave removed revealed a clear quasibiennial oscillation (QBO) strongest in the tropics, where it is comparable to the annual wave, persisting to mid‐latitudes in both hemispheres with some evidence of its existence at high latitudes. An estimation of the QBO period, using a superposition analysis (for no more than three cycles) for each latitude zone, revealed a decreasing period with latitude in both hemispheres. The maximum period of 27 months occurs in the tropics while the minimum in the northern hemisphere is about 20 months. This result suggests that the observed QBO in total ozone at high and low latitudes may not be directly related. This is of particular significance to studies of ozone trends since the result indicates interannual variations are latitude dependent.