Impact of different Asian source regions on the composition of the Asian monsoon anticyclone and of the extratropical lowermost stratosphere

Abstract

Abstract. The impact of different boundary layer source regions in Asia on the chemical composition of the Asian monsoon anticyclone, considering its intraseasonal variability in 2012, is analysed by simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS) using artificial emission tracers. The horizontal distribution of simulated CO, O3, and artificial emission tracers for India/China are in good agreement with patterns found in satellite measurements of O3 and CO by the Aura Microwave Limb Sounder (MLS). Using in addition, correlations of artificial emission tracers with potential vorticity demonstrates that the emission tracer for India/China is a very good proxy for spatial distribution of trace gases within the Asian monsoon anticyclone. The Asian monsoon anticyclone constitutes a horizontal transport barrier for emission tracers and is highly variable in location and shape. From the end of June to early August, a northward movement of the anticyclone and, during September, a strong broadening of the spatial distribution of the emission tracer for India/China towards the tropics are found. In addition to the change of the location of the anticyclone, the contribution of different boundary source regions to the composition of the Asian monsoon anticyclone in the upper troposphere strongly depends on its intraseasonal variability and is therefore more complex than hitherto believed. The largest contributions to the composition of the air mass in the anticyclone are found from northern India and Southeast Asia at a potential temperature of 380 K. In the early (mid-June to mid-July) and late (September) period of the 2012 monsoon season, contributions of emissions from Southeast Asia are highest; in the intervening period (early August), emissions from northern India have the largest impact. Our findings show that the temporal variation of the contribution of different convective regions is imprinted in the chemical composition of the Asian monsoon anticyclone. Air masses originating in Southeast Asia are found both within and outside of the Asian monsoon anticyclone because these air masses experience, in addition to transport within the anticyclone, upward transport at the southeastern flank of the anticyclone and in the tropics. Subsequently, isentropic poleward transport of these air masses occurs at around 380 K with the result that the extratropical lowermost stratosphere in the Northern Hemisphere is flooded by the end of September with air masses originating in Southeast Asia. Even after the breakup of the anticyclonic circulation (around the end of September), significant contributions of air masses originating in India/China are still found in the upper troposphere over Asia. Our results demonstrate that emissions from India, China, and Southeast Asia have a significant impact on the chemical composition of the lowermost stratosphere of the Northern Hemisphere, in particular at the end of the monsoon season in September/October 2012.

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

“…This choice of method is suitable to study the transport of air from the anticyclone, irrespective of where it originated at the surface. The impact of different boundary layer source regions on the Asian monsoon UTLS is an important research topic itself (e.g., Vogel et al, 2015;Tissier and Legras, 2016). The monsoon tropopause is mainly located above 380 K (see Appendix and Fig.…”

Long-range transport pathways of tropospheric source gases originating in Asia into the northern lower stratosphere during the Asian monsoon season 2012

“…The identification and the relative importance of different transport pathways of tropospheric source gases found within the Asian monsoon anticyclone into the lower stratosphere are the subject of a longstanding debate (Dethof et al, 1999;Park et al, 2004;Randel et al, 2010;Bian et al, 2012;Bourassa et al, 2012;Ploeger et al, 2013;Fairlie et al, 2014;Fromm et al, 2014;Uma et al, 2014;Vogel et al, 2014Vogel et al, , 2015Garny and Randel, 2016;Tissier and Legras, 2016;Orbe et al, 2015). The influence of these different transport pathways on the chemical composition of the extratropical upper troposphere and lower stratosphere (ExUTLS) is important because changes in ozone and water vapor in the ExUTLS have a significant impact on surface climate, even if the perturbation is relatively small.…”

Water vapor increase in the northern lower stratosphere by the Asian monsoon anticyclone observed during TACTS/ESMVal campaigns

“…In this study, we use the three-dimensional chemistry transport model CLaMS (McKenna et al, 2002a, b;Pommrich et al, 2014, and references therein) with the setup described in Vogel et al (2015). The simulations covered the time period from May 1 to October 31, 2012, capture the Asian monsoon season in 2012.…”

“…These different artificial tracers are freshly emitted every 24 h in the boundary layer and their concentrations in the atmosphere 25 represents the airmass contributions from the respective source regions. For more details see Vogel et al (2015Vogel et al ( , 2016. Vogel et al (2015) showed that the emission tracers for India and eastern China are correlated to AURA-MLS (Livesey et al, 2011) satellite measurements of potential vorticity (PV), O 3 , and CO.…”

“…For more details see Vogel et al (2015Vogel et al ( , 2016. Vogel et al (2015) showed that the emission tracers for India and eastern China are correlated to AURA-MLS (Livesey et al, 2011) satellite measurements of potential vorticity (PV), O 3 , and CO. Thus, they can be used as proxy for the location and shape of the AMA and allow for transport studies of air masses from the AMA into the northern extra-tropical lower stratosphere.…”