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Conditions for activation and transport

The geopotential height at 500 mb and 30 mb has been studied during the period corresponding to the filamentary structure on February 1996. A geopotential ridge, located at 135°W is remarkably correlated on both height levels. In the stratosphere it corresponds to the elongation of the polar vortex. Such structure is related to high ground pressure above Iceland and subsequent adiabatic lift and hence cooling of the airmasses. So this meteorological pattern is related to the formation of PSC, and the transport of airmasses outside the polar vortex. In fact, the polar vortex is displaced northern of Iceland. Airmasses are activated outside the polar vortex, or at his edge and hence more subject to filamentary transport. This circulation pattern in the troposphere is identified as Arctic Oscillation anomaly, related to low frequency variability in the atmosphere (Appenzeller et al., 2000).