Probing High Latitute Export of Air from the Asian Summer Monsoon (PHILEAS)

The Asian summer monsoon provides a strong link between the near-surface pollution and the global circulation. It affects both the composition of the deep stratosphere and of the extratropical lowermost stratosphere (LMS). To evaluate the associated global effects on climate, a detailed understanding of the associated pathways is essential. The extratropical upper troposphere / lower stratosphere (UT/LS) is mainly influenced by quasi-horizontal export of polluted and moist air from the high-level Asian Monsoon anticyclone, which is facilitated by frequent eddy shedding events. Previous High Altitude and Longe Range Research Aircraft (HALO) aircraft observations of anomalies in pollutants such as N₂O and CO over the Atlantic Ocean underlined the significant influence of the Asian monsoon on the composition of the extratropical LMS during summer and early autumn.

The recent HALO campaign PHILEAS (Probing high latitude export of air from the Asian summer monsoon) took place from August to October 2023. The focus was on three scientific questions: 1) How do gas-phase and particulate constituents evolve in large-scale eddies which are shed from the monsoon anticyclone? 2) How does eddy shedding from the monsoon impact the extratropical LMS composition in particular the water vapor and radiatively active species? and 3) What is the large-scale impact of the AMA on the LMS background state? These questions were addressed by numerous scientific flights from the campaign bases in Anchorage/Alaska and Oberpfaffenhofen/Germany. In our presentation, we give an overview on the campaign and discuss some early results.