Tropical Broadening in ERA Climatologies

Regional trends in the height of the tropopause in ERA-40 and ERA-Interim climatologies have been evaluated using a new tropopause definition that blends the traditional thermal tropopause with one based on potential vorticity. Two metrics have been used to quantify rates of change in the width of the tropics: one using zonal-mean tropopause trends, and one using a critical tropopause altitude. The rates of change are found to be sensitive to the metric and data set used, and to the time period considered.