Ozonesonde observations in the Arctic during 1989-2003: Ozone variability and trends in the lower stratosphere and free troposphere

We have studied the interannual and longer-term variations in ozone profiles over the Arctic from 1989 to 2003 using ozonesonde observations from seven northern high-latitude stations. The ozonesonde data have been carefully examined and made as internally consistent as possible. The homogenized measurements are analyzed with a statistical model. In both the stratosphere and troposphere the largest long-term changes have occurred in the late winter/spring period (January-April), the period of greatest interannual variability. In the stratosphere, layer ozone amounts correlate highly with proxies for the stratospheric circulation (100 hPa eddy heat flux averaged over 45-70°N), polar ozone depletion (the calculated volume of polar stratospheric clouds combined with the effective equivalent stratospheric chlorine) and tropopause height. At altitudes between 50 and 70 hPa, we estimate that chemical polar ozone depletion accounted for up to 50% of the March ozone variability. Negative trends in the lower stratosphere prior to 1997 can be attributed to the combined effect of dynamical changes, the impact of aerosols from the Mt. Pinatubo eruption and winters of relatively large chemical ozone depletion. Since 1996-1997 the observed increase in lower stratospheric ozone can be attributed primarily to dynamical changes. In the free troposphere, a statistically significant increase of 11.3 ± 1.8% over 15 years is observed which also maximizes in the January to April period (16.0 ± 3.1 % over 15 years). The model suggests that this can be attributed to the effects of changes in the Arctic Oscillation.