アイテム詳細

要旨

The Asian monsoon anticyclone (AMA) during northern summer is thought to be a major contributor for transport of tropospheric air masses, rich in water vapor, 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. During the StratoClim and ACCLIP campaigns the composition and aerosol content of the interior of the AMA could be characterized. From previous HALO missions TACTS/ESMVal and WISE a significant impact of the monsoon export on the background composition of the lowermost stratosphere (LMS) was observed.Observations and model simulations suggest that the so-called eddy shedding is of major importance for the export of AMA air masses into the LMS. Particularly, over the northern Pacific dynamical and diabatic forcings lead to a subsequent erosion of these eddies and to mixing into the background lower stratosphere. Furthermore, there is a high potential for impact from the Canadian wild fires on the composition of the UTLS in this region.We will present first results from the PHILEAS mission, which took place between August and October 2023 over Anchorage bracketed by a European measurement phase prior and after the Alaska phase. During PHILEAS, HALO was equipped by a combination of remote sensing and high resolution trace gas instruments as well as aerosol particle composition measurements. Flights covered the northern Pacific and Arctic region as well as the European-Mediterranean sector and the results aim to address the following 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? 3) What is the large scale impact of the AMA on the LMS background state?