PHILEAS (Probing high latitude export of air from the Asian summer monsoon)

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PHILEAS (Probing high latitude export of air from the Asian summer monsoon)The Asian monsoon anticyclone (AMA) during northern summer is thought to be the major pathway for tropospheric air masses, rich in water vapour, aerosol precursors and pollutants, into the UTLS. Recent observations show evidence for a strong contribution of ammonium nitrate transport by the AMA to the UTLS aerosol budget and the Asian Tropopause Aerosol Layer (ATAL), likely relevant for cirrus cloud formation. Recent aircraft campaign could characterize the composition and aerosol content of the interior AMA or will measure in the direct vicinity. In contrast, the impact of the monsoon related air masses on the global northern hemisphere has been observed during previous HALO missions. However, a study focusing on the transition of the AMA air masses into the northern lowermost stratosphere (LMS) and its consequences for aerosol processing and chemical composition is still missing. During the HALO missions TACTS/ESMVal and WISE it turned out, that the northern central Pacific is a key region for this transition.Observations and model simulations suggest a strong moistening effect of the so-called eddy shedding transport on the northern hemisphere UTLS. These eddies constitute isolated dynamical anomalies which are detached from the AMA and start to travel with the background flow. Initially, the respective chemical anomalies are relatively isolated within the shed eddy. Dynamical and diabatic forcings lead to a subsequent erosion of these isolated anomalies and mixing into the background stratosphere. Furthermore, the UTLS trace gas composition over the Pacific is affected by additional pathways in late summer and autumn: i) quasi-horizontal transport across the subtropical jet ii) convective transport by tropical typhoons eventually moving towards the extratropics, and iii) transport within extratropical weather systems. These combined processes impact the composition of the UTLS over the northern Pacific. We will investigate the relative importance of these processes contributing to the chemical gas-phase and aerosol composition of the UTLS. We will particularly characterize the dynamical and chemical evolution of the filaments formerly shed from the monsoon anticyclone during their transition into the stratosphere over the Pacific to estimate their impact on the overall gas phase and aerosol composition of the northern LMS.Summarizing, there are three major open scientific questions that motivate the PHILEAS project.1) What are the pathways, time scales and dynamical processes of air mass transport from the Asian summer monsoon into the extratropical UTLS?2) How do gas-phase and particulate constituents evolve in large-scale eddies which are shed from the monsoon anticyclone?3) How does eddy shedding from the monsoon impact the extratropical LMS composition in particular the water vapor and radiatively active species?