Abstract
The tropical western Pacific (TWP) is a preferential area of air uplifting from the surface to the upper troposphere. A significantly intensified upward motion through the troposphere over the TWP in the boreal wintertime (November to March of the next year) has been detected from 1958 to 2017 using the reanalysis datasets. Model simulations using the Whole Atmosphere Community Climate Model, version 4 (WACCM4) suggest that warming global sea surface temperatures (SSTs), particularly TWP SSTs, play a dominant role in the intensification of the upward motion by strengthening the Pacific Walker circulation and enhancing the deep convection over the TWP. Using CO as a tropospheric tracer, numeric simulations show that more CO could be elevated to the tropical tropopause layer (TTL) by the enhanced upward motion over the TWP and subsequently into the stratosphere by the strengthened Brewer-Dobson (BD) circulation which is also mainly caused by global SST warming. This implies that more tropospheric trace gases and aerosols may enter the stratosphere through the TWP region and affect the stratospheric chemistry and climate.
Highlights
The tropical western Pacific (TWP) is a critical region for tropical and global climate (e.g., Webster et al, 1996; Hu et al, 2020)
The recent trends of the upward motion from the lower to the upper troposphere in boreal winter over the TWP is investigated for the first time based on the reanalysis datasets and model simulations
The trend of the upward motion over the TWP is closely related to the changes in global sea surface temperatures (SSTs), especially the TWP SST warming
Summary
The tropical western Pacific (TWP) is a critical region for tropical and global climate (e.g., Webster et al, 1996; Hu et al, 2020). Though the TWP is not the dominant entry of trace gases transported from the troposphere into the lower stratosphere, numerous studies confirmed that the TWP region is an important pathway of the surface air entering the TTL (Fueglistaler et al., 2004; Levine et al, 2007; Krüger et al, 2008; Haines and Esler, 2014). Other studies found that the TWP region is an important source of the tropospheric trace gases in the TTL (e.g., Newton et al, 2018; Pan et al., 2016; Wales et al, 2018), even the polluted air from East Asia could be transported rapidly to Southeast Asia by meridional winds and subsequently be elevated to the tropical upper troposphere by the strong upward motion and the deep convection (Ashfold et al, 2015). To diagnose the changes in the BD circulation, the meridional and vertical velocities of the BD circulation are calculated by the TEM equations (Andrews and Mcintyre, 1976):
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