17.01.2013: FB1-Seminar

new place and time!!
now: 14:00 h in Hörsaal (West), Düsternbrooker Weg 20

Abstract:
The onset of the stratospheric final warming marks the winter-to-summer transition in the Arctic stratosphere, when the summer easterly circulation begins to develop. During this transition, the polar vortex breaks up into "remnants" which can persist as coherent vortices for several months. Recent studies have shown that following the spring onset, tropical/subtropical air could similarly be transported to high latitudes and remain confined, persisting for a long time within a stable "Frozen-In AntiCylone" (FrIAC) embedded in the summer easterlies. This work focuses on FrIAC occurrences and inter-annual variability to examine the processes driving such events. The MLS-AURA and MIPAS-ENVISAT satellite data, as well as the high-resolution advection contour model MIMOSA are used to characterize FrIACs and their life cycle. The model is driven by ERA-40 and the ERA-Interim reanalyses. In addition, we developed a method to detect the spatial extent of low-latitude intrusions into the polar region at the time of the spring transition. This allowed performing a FrIAC climatology over the period 1960-2011. During the 52 analysed years, 9 events have been identified: 1 in the 1960s, 1 in the 1980s, 2 in the 1990s and 5 from 2002. The 2011 FrIAC has been the strongest recorded in terms of spatial extent and origin of air masses trapped within. FrIACs are predominantly long-lived intrusions, which occur in association with abrupt and early reversal to summer easterlies with a strong enhancement of the wave activity around the date of this wind reversal. We also found that these events are favored if (i) no intense major warming occurs during wintertime and (ii) the quasi-bienniale oscillation is on its easterly phase.