An Analysis of Tropical Cold-Point Tropopause Warming in 1999

Yuanyuan Han,Feiyang Wang,Ruhua Zhang,Fei Xie,Jiankai Zhang,Shiyan Zhang

doi:10.1155/2017/4572532

Yuanyuan Han, Feiyang Wang + Show 4 more

Open Access

https://doi.org/10.1155/2017/4572532

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Abstract

Using reanalysis datasets, the warming of the tropical tropopause in 1999 and its evolution are investigated. It is found that there is a strong rate of increase in tropical cold-point tropopause temperature (CPTT) in June 1999, with negative CPTT anomalies before June (March-April-May) and large positive anomalies after June (July-August-September). Multiple linear regression analysis shows that deep convection, the quasi-biennial oscillation (QBO), and tropical upwelling associated with the Brewer-Dobson circulation (BDC) largely explain the variations of CPTT in 1999. Before June, enhanced deep convection resulting from increased sea surface temperature (SST) over the western Pacific and enhanced tropical upwelling of the BDC lead to a higher and colder tropopause. Those two factors explain 22% and 17% of the variance in CPTT, respectively. In June, the transformation of the east phase of QBO to the west phase contributes up to more than 50% of the variance in CPTT changes. After June, reduced tropical upwelling induced by weakened wave activity results in the warmer tropical tropopause temperatures to a large extent.

Highlights

Stratospheric processes can influence tropospheric weather and climate system through the dynamical processes [1,2,3,4,5] and via the radiative effects of the greenhouse gases in the stratosphere [6, 7]
The analysis above suggests that deep convection, the quasi-biennial oscillation (QBO), and upwelling associated with the Brewer-Dobson circulation (BDC) all contribute to the strong warming of the tropical tropopause in 1999
The high correlation coefficient (r = 0.96) between the regressed and observed cold-point tropopause temperature (CPTT) variations indicates that the variations of deep convection, the QBO, and the upwelling associated with the BDC can explain the CPTT in 1999 well

Summary

Introduction

Stratospheric processes can influence tropospheric weather and climate system through the dynamical processes [1,2,3,4,5] and via the radiative effects of the greenhouse gases in the stratosphere [6, 7]. Xie et al [36] found that the leading principal component (PC1) of CPTT variability since the 1980s is associated with the tropical CPTH They further pointed out that QBO and ENSO are two additional factors that account for CPTT variability. The upwelling of large-scale BrewerDobson circulation (BDC) in the stratosphere can influence the temperature and compositions of the tropopause layer [37] Except for their long-term trend and interannual variability [28, 35, 38,39,40], tropical tropopause temperature sometimes shows extreme warming or cooling in a year; for example, Randel et al [19] found an abrupt decrease in tropical tropopause temperature (approximately −1 K) in 2001, leading to a sudden decrease of stratospheric water vapor during the same period.

Data and Methods

The Contributions of Different Impact Factors to Tropopause Warming in 1999

Findings

Conclusions