Abstract
Abstract. Enhanced tropospheric trace gases such as CO, CH4 and H2O and reduced stratospheric O3 were measured in situ in the lowermost stratosphere over northern Europe on 26 September 2012 during the TACTS aircraft campaign. The measurements indicate that these air masses clearly differ from the stratospheric background. The calculation of 40-day backward trajectories with the trajectory module of the CLaMS model shows that these air masses are affected by the Asian monsoon anticyclone. Some air masses originate from the boundary layer in Southeast Asia/West Pacific and are rapidly lifted (1–2 days) within a typhoon up to the outer edge of the Asian monsoon anticyclone. Afterwards, the air parcels are entrained by the anticyclonic circulation of the Asian monsoon. The subsequent long-range transport (8–14 days) of enhanced water vapour and pollutants to the lowermost stratosphere in northern Europe is driven by eastward transport of tropospheric air from the Asian monsoon anticyclone caused by an eddy shedding event. We found that the combination of rapid uplift by a typhoon and eastward eddy shedding from the Asian monsoon anticyclone is a novel fast transport pathway that may carry boundary emissions from Southeast Asia/West Pacific within approximately 5 weeks to the lowermost stratosphere in northern Europe.
Highlights
One of the most pronounced circulation patterns in the upper troposphere and lower stratosphere (UTLS) during boreal summer is the Asian summer monsoon circulation
To corroborate our finding that trajectories starting in Pacific typhoons, circulating around the Asian monsoon anticyclone, released by eddy shedding events and transported eastwards by the subtropical jet can reach the region of interest over northern Europe during the TACTS measurements on 26 September 2012, we calculated forward trajectories starting within the typhoon Bolaven and Tembin between 22 and 26 August 2012 at noon
On 26 September 2012, a filament with enhanced tropospheric trace gases such as CH4, carbon monoxide (CO), and H2O and reduced stratospheric O3 was measured over northern Europe in the extratropical lowermost stratosphere during a flight on board the German Research Aircraft HALO during the TACTS campaign
Summary
One of the most pronounced circulation patterns in the upper troposphere and lower stratosphere (UTLS) during boreal summer is the Asian summer monsoon circulation. It consists of a large-scale anticyclone in the UTLS extending from Asia to the Middle East from early June until the end of September. The Asian monsoon anticyclone extends into the lowermost stratosphere The Asian monsoon circulation provides an effective pathway for water vapour (Ploeger et al, 2013) and pollutants to the lower stratosphere of the Northern Hemisphere. Water vapour (H2O) is the most important greenhouse gas and moistening of the stratosphere is an important driver of climate change Increasing amounts of the greenhouse gas methane (CH4) enhance stratospheric water vapour concentrations by methane oxida-
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