Tropopause variations in Tibet from COSMIC GPS Radio Occultation observations

Abstract

The Tropopause in Tibet has complex and variable characteristics due to its harsh natural conditions, while it is hard to monitor the tropopause in Tibet from traditional techniques. Nowadays, the high resolution data from GPS Radio Occultation provide a unique opportunity to monitor the tropopause variation, particularly over Tibet. In this paper, the high resolution cold-point tropopause (CPT) in Tibet are investigated using temperature profiles derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation measurements from June 2006 to Feb 2015. The structure of upper troposphere and lower stratosphere (UTLS) is analyzed, which provides observations of stratosphere and troposphere exchange (STE) over the Tibetan Plateau. The multiple tropopauses occur in winter with a high frequency over the Tibetan Plateau. The reasons for the multiple tropopauses and temperature variations are the variations of zonal winds or atmospheric gravity waves. Multiple tropopause events during winter season are associated with tropopause folds near the subtropical westerly jet. The multiple tropopauses consistently varied with the movement of the jet. The multiple tropopauses become a single tropopause with the development of the monsoon, which helps to forbid the atmosphere constituents to defuse in stratosphere and upper atmosphere. In addition, the temperature of CPT increases from the last decade. These zonal winds not only affect the temperature but also affect the heights. Meanwhile Gravity waves activity increases in the Tibetan Plateau. Atmospheric Research reanalysis and MERRA/AIRS winds shows that the waves are primarily forced by strong flow across the topography. The variation of tropopause in the Tibet plateau is mostly associated with the wind components.