Properties of the arctic tropopause

A climatology of Arctic tropopause properties is derived using European Centre for Medium‐Range Weather Forecasts Re‐analyses, and is shown to be consistent with that from the Historical Arctic Radiosonde Archive. It is demonstrated that the thermal tropopause is generally easy to define from the temperature profile, even in the polar night, in contrast with the situation in Antarctic winter. In winter, the tropopause tends to have higher pressure and temperature in the western hemisphere and lower values in the eastern hemisphere. In summer the situation is more zonally symmetric with the higher pressure and temperature tropopause region near the pole. Strong annual cycles are seen in both temperature and pressure. these cycles being out of phase temporally. It is hypothesized that the tropopause temperature is largely determined by the approximately isothermal lower‐stratospheric temperature, while the pressure is more strongly influenced by changes in the tropospheric lapse rate due to dynamical mechanisms. The multi‐decade radiosonde dataset (1965–1990) shows some evidence of a long‐term trend in tropopause properties. The wintertime tropopause pressure has decreased by approximately 14 mb per decade, while that in other seasons has decreased by around 5 mb per decade. The tropopause temperature only shows a significant trend during winter, having decreased by 1.6 K per decade since 1965. These changes are discussed in relation to changes in ozone and greenhouse gases, and the strength of the stratospheric vortex. In particular, the winter tropopause properties appear to be strongly correlated with the Arctic Oscillation Index.