Variability and trends in the global tropopause estimated from radiosonde data

This study examines global tropopause variability on synoptic, monthly, seasonal, and multidecadal timescales using 1980-2004 radiosonde data. On synoptic and monthly timescales, tropopause height variations are anticorrelated with stratospheric temperature variations and positively correlated with tropospheric temperature variations. Correlations are stronger in the extratropics than in the tropics, for the upper troposphere (500-300 hPa) than for the lower troposphere, and for the lower stratosphere than for the middle stratosphere. The extratropical tropopause is more sensitive to temperature changes than the tropical tropopause, and in both regions, monthly anomalies of tropopause height are more sensitive to stratospheric temperature change than tropospheric, rising 2-3 km per degree cooling of the lower stratosphere. Tropopause height trends over 1980-2004 are upward at almost all of the (predominantly extratropical) stations analyzed, yielding an estimated global trend of 64 +/- 21 m/decade, a corresponding tropopause pressure trend of -1.7 +/- 0.6 hPa/decade, and tropopause temperature decrease of 0.41 +/- 0.09 K/decade. These tropopause trends are accompanied by significant stratospheric cooling and smaller tropospheric warming. However, the tropopause trends are spatially correlated with stratospheric temperature trends and uncorrelated with tropospheric temperature trends. This association of tropopause height and stratospheric temperature trends, together with the presence of a significant quasi-biennial oscillation signal in tropopause height, suggests that at these lowest frequencies the tropopause is primarily coupled with stratospheric temperatures. Therefore, as an indicator of climate change, long-term changes in the tropopause may carry less information about changes throughout the vertical temperature profile than has been suggested by previous studies using reanalyses and global climate models.