Exploring the relationship between the cloud-top and tropopause height in boreal summer over the Tibetan Plateau and its adjacent region

Abstract

The distribution characteristics of cloud-top and tropopause height in the tropics and subtropics in boreal summer are analyzed based on CALIPSO data for the period 2008–2012. The maximum values of cloud-top vertical cumulative frequency above the tropopause (CTAT) are concentrated in three tropical regions: the Asian summer monsoon region, Central America, and western Africa. The contributions to the area-weighted CTAT frequency in the three regions from the Northern Hemisphere are 49.0%, 13.5%, and 12.4%, respectively. Moreover, the contribution of troposphere-to-stratosphere transport (TST) in the Asian monsoon region to global TST can be far greater than 50%, according to analysis of the continuous equation, velocity potential, and divergent wind from ERA-Interim data. Furthermore, the Asian summer monsoon circulation system controls the distribution of the cloud top. On the south side of the Tibetan Plateau, the maximum frequency of the cloud top, more than 10% per 500 m vertically, is most likely to appear in the core of the high-level easterly jet near the tropopause height (16.5 km). Over the Tibetan Plateau, the maximum frequency of the cloud top, greater than 3% per 500 m vertically, is suppressed below 11 km, far away from the thermodynamic tropopause height but close to the dynamic tropopause height of 2 PVU (potential vorticity units).

Keywords

• Cloud top
• tropopause
• troposphere-to-stratosphere transport
• Asian summer monsoon circulation
• Tibetan Plateau