Enhanced upward motion through the troposphere over the tropical western Pacific and its implications for the transport of trace gases from the troposphere to the stratosphere

Abstract

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 following year, NDJFM) has been detected using multiple reanalysis datasets. The upward motion over the TWP is intensified at rates of 8.0 ± 3.1 % per decade and 3.6 ± 3.3 % per decade in NDJFM at 150 hPa from 1958 to 2017, using JRA55 and ERA5 reanalysis datasets, while the MERRA-2 reanalysis data show a 7.5 ± 7.1 % per decade intensified upward motion for the period 1980–2017. Model simulations using the Whole Atmosphere Community Climate Model, version 4 (WACCM4), suggest that warming global sea surface temperatures (SSTs), particularly SSTs over the eastern maritime continent and tropical western Pacific, 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, the WACCM4 simulations show that an increase in CO at a rate of 0.4 ppbv (parts per billion by volume) per decade at the layer 150–70 hPa in the tropics is mainly resulted from the global SST warming and the subsequent enhanced upward motion over the TWP in the troposphere and strengthened tropical upwelling of Brewer–Dobson (BD) circulation in the lower stratosphere. This implies that more tropospheric trace gases and aerosols from both natural maritime sources and outflow from polluted air from South Asia may enter the stratosphere through the TWP region and affect the stratospheric chemistry and climate.