Abstract
The tropical cold-point tropopause temperature (CPTT), a potentially important indicator of global climate change, is of particular importance for understanding changes in stratospheric water vapor levels. Since the 1980s, the tropical CPTT has shown not only interannual variations, but also a decreasing trend. However, the factors controlling the variations in the tropical CPTT since the 1980s remain elusive. The present study reveals that the continuous expansion of the area of the Indo-Pacific warm pool (IPWP) since the 1980s represents an increase in the total heat energy of the IPWP available to heat the tropospheric air, which is likely to expand as a result. This process lifts the tropical cold-point tropopause height (CPTH) and leads to the observed long-term cooling trend of the tropical CPTT. In addition, our analysis shows that Modoki activity is an important factor in modulating the interannual variations of the tropical CPTT through significant effects on overshooting convection.
Highlights
The tropical cold-point tropopause temperature (CPTT), a potentially important indicator of global climate change, is of particular importance for understanding changes in stratospheric water vapor levels
Since the 1980s, the second leading ode of tropical SST variations show a warm center in the central Pacific, with two cold centers, one in the eastern Pacific and one in the western Pacific; this is distinct from the pattern observed during canonical El Nino episodes, which are characterized by a cold center in the eastern Pacific and a warm center in the western Pacific[16]
It is interesting that the regions with the largest decrease in tropical CPTT since the 1980s are concentrated over the Indo-Pacific warm pool (IPWP) (Figs. 2b and c)
Summary
Indo-Pacific Warm Pool Area Expansion, Modoki Activity, and Tropical Cold-Point Tropopause Temperature Variations. The present study reveals that the continuous expansion of the area of the Indo-Pacific warm pool (IPWP) since the 1980s represents an increase in the total heat energy of the IPWP available to heat the tropospheric air, which is likely to expand as a result This process lifts the tropical cold-point tropopause height (CPTH) and leads to the observed long-term cooling trend of the tropical CPTT. There is no significant correlation between the tropical-averaged CPTT and convection in the region (Fig. 1d) These results suggest that whether the changes in SST over the western Pacific leading to the tropical-averaged CPTT variations remain uncertain. 1980s are related to El Nino Modoki events These uncertainties, along with observed climate change, motivated the present analysis of the trend and interannual variations in the tropical CPTT since the 1980s
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