Stratospheric water vapour as tracer for Vortex filamentation in the Arctic winter 2002/2003

[摘要] Balloon-borne frost point hygrometers measured three high-resolution profiles ofstratospheric water vapour above Ny-Ålesund, Spitsbergen during winter 2002/2003. Theprofiles obtained on 12 December 2002 and on 17 January 2003 provide an insight into thevertical distribution of water vapour in the core of the polar vortex. The water vapour sounding on 11 February 2003 was obtained within the vortex edge regionof the lower stratosphere. Here, a significant reduction of water vapour mixing ratio wasobserved between 16 and 19 km. The stratospheric temperatures indicate that this dehydrationwas not caused by the presence of polar stratospheric clouds or earlier PSC particlesedimentation.

Ozone observations on this day indicate a large scale movement of the polar vortex and showlaminae in the same altitude range as the water vapour profile. The link between the observedwater vapour reduction and filaments in the vortex edge region is indicated in the results ofthe semi-lagrangian advection model MIMOSA, which show that adjacent filaments of polarand mid latitude air can be identified above the Spitsbergen region. A vertical cross-sectionproduced by the MIMOSA model reveals that the water vapour sonde flew through polar airin the lowest part of the stratosphere below 425 K, then passed through filaments of midlatitude air with lower water vapour concentrations, before it finally entered the polar vortexabove 450 K. These results indicate that on 11 February 2003 the frost point hygrometermeasured different water vapour concentrations as the sonde detected air with differentorigins. Instead of being linked to dehydration due to PSC particle sedimentation, the localreduction in the stratospheric water vapour profile was in this case caused by dynamical processesin the polar stratosphere.

[学科分类] 大气科学