Variations of the total ozone trend over the northern hemisphere midlatitudes in winter‐spring seasons 1963–1964 through 1992–1993

Abstract

Monthly means of total ozone for winter‐spring seasons (December through the next March) since 1963–1964 through 1992–1993 from a network of 19 Dobson stations are averaged to form a composite time series of the winter‐spring midlatitudinal total ozone. A multiple regression statistical model, comprising overall mean level, linear trend, quasi‐biennial, El Niño, solar (including both the 11‐year and its double length “geomagnetic” oscillations), and dynamics of the winter polar vortex terms, is applied to estimate interannual variations of total ozone over the northern hemisphere midlatitudes in winter‐spring seasons. The model used explains about 88% of total variance of the winter‐spring total ozone and gives the value of the anthropogenic trend in the northern hemisphere midlatitudinal total ozone of the order of −3.5%±0.4% per decade since winter‐spring of 1969–1970. The model's results support the hypothesis that the increase of the ozone loss during the 1980s and 1990s over the northern hemispheric midlatitudes may be partially caused by a superposition of “natural” long‐term oscillations in total ozone related to the climatic changes in the atmospheric dynamics. The initial evidences for a strong manifestation of the interannual changes of the polar vortex in the winter‐spring midlatitudinal total ozone data are found. The 22‐year oscillation in the total ozone data is disclosed; however, because of the limited length of the ozone data, one should be cautious to relate this fluctuation uniquely to the solar input.