The Long-Term Coupling between Column Ozone and Tropopause Properties

Abstract

The observational data of the vertical temperature distribution and column ozone, obtained from 10 main stations in the Northern Hemisphere, are analyzed in order to explore the tropopause variations in conjunction with the dynamical variability in column ozone. From the analysis presented, it is evident that the summer distribution of the frequency of occurrence of the tropopause over Greece, apart from its main maximum (around 12 km), is also characterized by a secondary one around 16 km. It is proposed that this elevated maximum possibly originates from the height variation of the tropopause from 12 to 16 km depending on whether the Athens station is located below the cyclonic shear side or below the anticyclonic shear side of the subtropical jet stream. It is also suggested that the transport in the upper troposphere and lower stratosphere that originated in the equatorial region forces the appearance of the multiple tropopauses above Greece. Furthermore, the observational analysis of the vertical ozone distribution above Greece shows that the upward movement of the ozone profile is accompanied by an increase in the annually averaged tropopause height, which leads to an excessive column ozone trend around 0.5%–1.0% decade−1. Additionally, the linear regression analyses of the deseasonalized monthly mean column ozone and tropopause height indicate that the tropopause variations might be responsible for about a quarter of the observed total ozone content (TOC) trend over Greece, the same magnitude of midlatitude ozone depletion that 2D dynamical and chemical models cannot reproduce. This part of the trend is only due to the variations in the upper-troposphere/lower-stratosphere region and not attributable to all dynamical changes and forcing on TOC. Finally, the inverse relationship between column ozone and tropopause height at various geographical sites shows a longitudinal and latitudinal variability, with the strongest signal observed in the eastern midlatitudes of the Northern Hemisphere. At these geographical sites, changes in both the column ozone and lower-stratospheric temperature are roughly 10 Dobson unit (DU) K−1.