Quantification of water vapour transport from the Asian monsoon to the stratosphere

Matthias Nützel,Felix Ploeger,Hella Garny,Aurélien Podglajen

doi:10.5194/acp-19-8947-2019

Abstract

Abstract. Numerous studies have presented evidence that the Asian summer monsoon anticyclone substantially influences the distribution of trace gases – including water vapour – in the upper troposphere and lower stratosphere (e.g. Santee et al., 2017). Stratospheric water vapour in turn strongly affects surface climate (see e.g. Solomon et al., 2010). Here, we analyse the characteristics of water vapour transport from the upper troposphere in the Asian monsoon region to the stratosphere employing a multiannual simulation with the chemistry-transport model CLaMS (Chemical Lagrangian Model of the Stratosphere). This simulation is driven by meteorological data from ERA-Interim and features a water vapour tagging that allows us to assess the contributions of different upper tropospheric source regions to the stratospheric water vapour budget. Our results complement the analysis of air mass transport through the Asian monsoon anticyclone by Ploeger et al. (2017). The results show that the transport characteristics for water vapour are mainly determined by the bulk mass transport from the Asian monsoon region. Further, we find that, although the relative contribution from the Asian monsoon region to water vapour in the deep tropics is rather small (average peak contribution of 14 % at 450 K), the Asian monsoon region is very efficient in transporting water vapour to this region (when judged according to its comparatively small spatial extent). With respect to the Northern Hemisphere extratropics, the Asian monsoon region is much more impactful and efficient regarding water vapour transport than e.g. the North American monsoon region (averaged maximum contributions at 400 K of 29 % versus 6.4 %).

Highlights

Atmospheric water vapour is a key greenhouse gas (e.g. Held and Soden, 2000; Schmidt et al, 2010; Müller et al, 2016)
E.g. by Bannister et al (2004) and Wright et al (2011), have used tagging approaches for stratospheric water vapour; the water tagging employed here is suited for our research aims, since it allows a decomposition of water origins consistent with the model treatment of water transport and removal through freeze-drying
Comparisons of MLS and CLaMS water vapour fields during June– August (JJA) and December–February (DJF) at 380 K have been previously presented, e.g. in Poshyvailo et al (2018; see e.g. their Fig. 5). These comparisons show a reasonable agreement of simulated and observed water vapour fields and, especially, the water vapour signals of the Asian and North American monsoon regions during Northern Hemisphere (NH) summer are present in the modelled water vapour distributions (Poshyvailo et al, 2018)

Summary

Introduction

Atmospheric water vapour is a key greenhouse gas (e.g. Held and Soden, 2000; Schmidt et al, 2010; Müller et al, 2016). Changes in water vapour can alter stratospheric chemistry and the abundances of other radiatively active trace gases As proposed by Brewer (1949), TTL temperatures strongly influence water vapour abundances in the stratosphere. This can be seen by the so-called water vapour tape recorder (Mote et al, 1996, see Fig. 3), i.e. an annual seesaw of positive and negative water vapour anomalies that ascends in the tropical pipe (Plumb, 1996) and is related to the seasonal cycle of TTL temperatures This can be seen by the so-called water vapour tape recorder (Mote et al, 1996, see Fig. 3), i.e. an annual seesaw of positive and negative water vapour anomalies that ascends in the tropical pipe (Plumb, 1996) and is related to the seasonal cycle of TTL temperatures (e.g. Yulaeva et al, 1994)

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Results

Discussion

Conclusion