Publication Date:
2016-02-01
Description:
This paper presents a set of observations by the CRISTA infrared limb sounder in low-earth orbit taken in August 1997 and analyses of trace-gases in the Asian Summer Monsoon (ASM) region. 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 within the ASM originating in India and China. Comparing the retrieved PAN VMRs with potential vorticity (PV) on isentropes reveals that the PAN VMRs exhibit the strongest decrease at each isentrope for an increasing value of PV which may 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 its location agrees well with the limits of the area of increased PAN VMRs both horizontally on isentropes and vertically within the 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 parcels, whereas the region in between the anticyclone and the eddy contains many mixed 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 time scale of only a few days.
Electronic ISSN:
1680-7375
Topics:
Geosciences
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