Impact of typhoons on the composition of the upper troposphere within the Asian summer monsoon anticyclone: the SWOP campaign in Lhasa 2013

摘要

In the frame of the SWOP (sounding water vapour, ozone, and particle)campaign during the Asian summer monsoon (ASM), ozone and water vapourprofiles were measured by balloon-borne sensors launched from Lhasa(29.66° N, 91.14° E, elevation 3650 m), China, in August2013. In total, 24 soundings were launched, nearly half of which show strongvariations in the relationship between ozone and water vapour in thetracer–tracer correlation in the upper troposphere and lower stratosphere(UTLS). For each sounding, 20-day backward trajectories were calculated usingthe trajectory module of the Chemical Lagrangian Model of the Stratosphere(CLaMS) to analyse these variations. The trajectory calculations demonstratethat three tropical cyclones (tropical storm Jebi, typhoons Utor and Trami),which occurred over the western Pacific Ocean during August 2013, had aconsiderable impact on the vertical distribution of ozone and water vapour byuplifting marine air masses to altitudes of the ASM anticyclone. Air parcelssubsequently arrived at the observation site via two primary pathways:firstly via direct horizontal transport from the location of the typhoon tothe station within approximately 3 days, and secondly via transportfollowing the clockwise wind flow of the ASM within a timescale of 1 week.Furthermore, the interplay between the spatial position of the ASManticyclone and tropical cyclones plays a key role in controlling thetransport pathways of air parcels from the boundary layer of the westernPacific to Lhasa in horizontal and vertical transport. Moreover, thestatistical analysis shows that the strongest impact by typhoons is found ataltitudes between 14.5 and 17 km (365–375 K). Low ozone values(50–80 ppbv) were observed between 370 and 380 K due to the strongvertical transport within tropical cyclones.