Articles | Volume 16, issue 13
Atmos. Chem. Phys., 16, 8389–8403, 2016
https://doi.org/10.5194/acp-16-8389-2016
Atmos. Chem. Phys., 16, 8389–8403, 2016
https://doi.org/10.5194/acp-16-8389-2016

Research article 12 Jul 2016

Research article | 12 Jul 2016

Observations of PAN and its confinement in the Asian summer monsoon anticyclone in high spatial resolution

Jörn Ungermann, Mandfred Ern, Martin Kaufmann, Rolf Müller, Reinhold Spang, Felix Ploeger, Bärbel Vogel, and Martin Riese Jörn Ungermann et al.
  • Institut für Energie- und Klimaforschung – Stratosphäre (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germany

Abstract. This paper presents an analysis of trace gases in the Asian summer monsoon (ASM) region on the basis of observations by the CRISTA infrared limb sounder taken in low-earth orbit in August 1997. The spatially highly resolved measurements of peroxyacetyl nitrate (PAN) and O3 allow a detailed analysis of an eddy-shedding event of the ASM anticyclone. We identify enhanced PAN volume mixing ratios (VMRs) within the main anticyclone and within the eddy, which are suitable as a tracer for polluted air originating in India and China. Plotting the retrieved PAN VMRs against potential vorticity (PV) and potential temperature reveals that the PV value at which the PAN VMRs exhibit the strongest decrease with respect to PV increases with potential temperature. These PV values might be used to identify the extent of the ASM. Using temperature values also derived from CRISTA measurements, we also computed the location of the thermal tropopause according to the WMO criterion and find that it confines the PAN anomaly vertically within the main ASM anticyclone. In contrast, the shed eddy exhibits enhanced PAN VMRs for 1 to 2 km above the thermal tropopause. Using the relationship between PAN as a tropospheric tracer and O3 as a stratospheric tracer to identify mixed air parcels, we further found the anticyclone to contain few such air parcels, whereas the region between the anticyclone and the eddy as well as the eddy itself contains many mixed air parcels. In combination, this implies that while the anticyclone confines polluted air masses well, eddy shedding provides a very rapid horizontal transport pathway of Asian pollution into the extratropical lowermost stratosphere with a timescale of only a few days.

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This paper presents an analysis of temperature and the trace gases PAN and O3 in the Asian Summer Monsoon (ASM) region. The positive PAN anomaly consisting of polluted air is confined vertically within the main ASM anticyclone, whereas a recently shed eddy exhibits enhanced PAN VMRs for 1 to 2 km above the thermal tropopause. This implies that eddy shedding provides a very rapid horizontal transport pathway of Asian pollution into the extratropical lowermost stratosphere.
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