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

Abstract. The impact of air masses from Asia influenced by the Asian monsoon anticyclone on the northern hemispheric stratosphere is investigated based on in-situ measurements. An statistical significant increase in water vapor of about 0.5 ppmv (11 %) and methane up to 20 ppbv (1.2 %) in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation in the northern hemisphere during the HALO aircraft mission TACTS and ESMVal. We investigate the origin of this water vapor and methane increase with the help of the three-dimensional Lagrangian chemistry transport model CLaMS. We assign the source of the moist air masses in the Asian region (North and South India, East China, South East Asia and tropical Pacific) based on tracers of airmass origin used in CLaMS. The water vapor increase is correlated to an increase of the simulated Asian monsoon air mass contribution from 10 % in August to 20 % in September, which corresponds to a doubling of the influence of air masses affected by the Asian monsoon region. Additionally, back trajectories starting at the aircraft flight paths are used to differentiate between transport from the Asian monsoon anticyclone and other source regions by calculating the Lagrangian cold point (LCP). The geographic location of the LCPs, which indicates the region where the imprint of water vapor concentration along these trajectories occur, can be exclusively attributed to the Asian monsoon region.