Generation of layering in the upper Arctic troposphere away from the jet stream

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Ozone sounding databases for two stations, Sodankylä (67° N, 27° E) and Ny-Ålesund (79° N, 12° E) wereused in order to investigate the generation of layering in the upper and middle troposphere ofthe Arctic. We concentrated on dry, ozone-rich and stable layers observed below the thermal tropopauseunder light wind conditions. This condition ensures that the observed layer is not a tropopause fold, awell-known phenomenon that develops within frontal zones near the jet stream. Selection criteria for ozone,humidity and stability anomalies of the tropopause fold detection algorithm were used here to pick out fordetailed studies the most pronounced examples of laminae. For all these cases the meteorological situationswere investigated in order to establish the origin of the observed layers. We found that layers could beclassified into two groups. Laminae of the first group were observed equatorward of the jet stream and thoseof a second group were observed poleward of the jet. The meteorological situation for the first groupresembles that for equatorward stratospheric streamer propagation. It was found that this group accounts foronly a small fraction of the layers observed at Sodankylä and for none of those observed at Ny-Ålesundduring the period investigated. A large case-to-case variability in the synoptic situation was observed for thesecond group of laminae, which were detected northward of the jet stream. Nevertheless, in about half ofthe cases, streamers of tropospheric air were found in the vicinity of the stations on the isentropic surfacesjust above the detected stratospheric layers. Back trajectory analyses showed that these layers originated inthe vicinity of the polar jet stream. We suppose that laminae-like structures in the troposphere were caused,in both groups, by equatorward (poleward) advection of the stratospheric (tropospheric) air, together withdifferential vertical shear. Forward-trajectory calculations suggest that, subsequently, a part of thestratospheric layers can mix irreversibly into the troposphere.

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Karpetchko, A. , Kyro, E. and von der Gathen, P. (2003): Generation of layering in the upper Arctic troposphere away from the jet stream , Annales Geophysicae, 21 , pp. 1653-1665 .

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