Analysis of factors influencing tropical lower stratospheric water vapor during 1980\u20132017

Jinpeng Lu,Cheng Sun,Qifa Cai,Jiali Luo,Jiankai Zhang,Fei Xie,Hongying Tian,Juan Li

doi:10.1038/s41612-020-00138-7

Abstract

Tropical cold point tropopause temperature (CPT) anomalies determine lower stratospheric water vapor (LSWV) variations, leading to a high correlation between variations in tropical average CPT and changes in tropical average LSWV. However, this high correlation is only found in winter and spring. This work revisits the factors controlling LSWV variations using observations and simulations over the past ~40 years. It is found that the first and second empirical orthogonal function (EOF) modes of tropical CPT variations together explain the tropical average LSWV changes much better than the tropical average CPT variations. The high correlation between the first and second EOF modes of tropical CPT variations and tropical average LSWV changes holds in all four seasons. A further analysis shows that the first and second EOF modes of tropical CPT variations are related to canonical El Niño–Southern Oscillation (ENSO) activity and sea surface temperature (SST) variations in the central Pacific Ocean, respectively. ENSO Modoki is also an important factor that affects LSWV variations by influencing the vertical velocity at the tropopause. The quasi-biennial oscillation (QBO) affects the CPT, and is the third process modulating the LSWV changes. The simulations also support the results.

Highlights

Stratospheric water vapor (SWV) plays an important role in regulating the global radiation budget, energy balance, stratospheric temperature and chemical processes, and global climate change[1,2,3,4,5]
Ding and Fu77 found that sea surface temperature (SST) warming in the tropical central Pacific cools the tropical tropopause layer (TTL) by enhancing the equatorial-wave-induced upward motion near the tropopause, which reduces the amount of water vapor entering the stratosphere
We investigated factors affecting lower SWV (LSWV) variations from 1980 to 2017 using MERRA-2 reanalysis data and from 1955 to 2005 with WACCM4 simulation data, and identified mechanisms affecting water vapor in the lower stratosphere

Summary

Introduction

Stratospheric water vapor (SWV) plays an important role in regulating the global radiation budget, energy balance, stratospheric temperature and chemical processes, and global climate change[1,2,3,4,5]. Understanding the variations and controlling factors of SWV is important for the prediction of global climate change. The main source of water vapor in the middle and upper stratosphere is methane oxidation in the stratosphere[8,9], but in the lower and middle stratosphere the main source is the transport of air through upwelling from the tropical tropopause layer (TTL) into the stratosphere[10,11]. Vertical transport is a factor affecting the variations of water vapor in the lower stratosphere. Many studies have investigated LSWV variations and their link with global climate change[13,14,15,16]

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Results

Conclusion