Is the tropopause higher over the Tibetan Plateau? Observational evidence from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) data

摘要

Using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data from June 2006 to December 2009, the temperature structure and the tropopause height over the Tibetan Plateau (TP) is studied in this paper. The temperature over the TP is warmer and experiences a lager magnitude of change than that over the same latitudinal plain area (hereinafter referred to as the Plain) at the same level of lower troposphere. The lapse rate tropopause (LRT) shows a strong correlation with thermal properties of the atmosphere. Its height variation is anticorrelated with its temperature, highest at ～19 km and coldest at approximately —72℃ in boreal summer, but lowest at ～13 km and approximately —56℃ in boreal winter. Those of the cold point tropopause (CPT) exhibit a positive correlation but barely seasonal variation all year long. As an outstanding heat source in boreal summer, the TP thermally pushes the LRT upward by —2 km compared with the Plain, while the LRT drops below that over the Plain in boreal winter. The LRT height is also strongly dependent on the subtropical jet that is associated with the tropopause fold and/or multiple tropopauses, leading to fairly bimodal distribution of the LRT probability density function. As the "roof of the world," the elevated topography of the TP dynamically lifts the CPT to a higher altitude without significantly seasonal variations. Along the latitude of 32.5°N the CPT is located at —18 km over the main body of the TP and drops to —15 km over the Plain. Given the area in the TP (30°-35°N, 87°-95°E) as well as in the Plain (30°-35°N, 112°-120°E), the CPT primarily resides at 17-18 km, 72.52% over the TP and 69.22% over the Plain. Their monthly mean difference can reach 1.4 km for the complete analysis period.