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Abstract

The global structure and variability of the tropopause observed using CHAMP/GPS radio occultation observations are presented. Comparison of tropopause temperature and height with radiosonde observations located at tropical and sub-tropical latitudes reveals the high accuracy of CHAMP/GPS measurements, especially at a sharp tropopause which is more often seen in tropical latitudes. The role of tropical deep convection on the observed tropopause structure has been investigated using outgoing long-wave radiation (OLR) data. Significant correlations are found between them quantifying the accuracy of CHAMP/GPS measurements independently and also the large scale tropical temperature response to transient convection. The tropopause height is found to be nearly uniform throughout the tropics, with varying temperatures, both having a pronounced annual cycle. At polar latitudes, the tropopause structure and variability is found to be completely different. Even though the determination of the Antarctic tropopause using thermal criteria is difficult especially during winter, there is no problem in determining the Arctic tropopause. The results show an annual cycle in the Arctic tropopause temperature with maximum during winter and minimum during summer, whereas the Antarctic tropopause exhibits a reversal, i.e., maximum during summer and minimum during winter. The sharpness of the tropopause is determined using the change of the vertical temperature gradient across the tropopause and is found to be highest in summer and lowest in winter with slight difference between hemispheres. The thermal tropopause obtained from CHAMP/GPS has been compared with the dynamical tropopause determined through ECMWF reanalysis data. It is also found that tropopause structure, within the polar latitudes, differs from place to place in one season.