The Polar Vortex (PN-PV)

Principal Participants: Manson, Sica, Shepherd, Ward, Manney; Stakeholders: Brunet, Denis, Jean, Methot; Canadian Gov't Departments: EC, CSA; International Orgs: CAWSES-II of SCOSTEP; HQP: PDF + 2 graduate students.

Rationale The polar vortex, the dominant organizing structure in the atmosphere during Arctic night, extends from the middle troposphere to the mesopause region (5-95km (Xu et al., 2009)). It forms as a result of the autumnal cooling of the atmosphere at higher latitudes, which produces a strong westerly wind vortex and also tends to isolate the air of the Middle Atmosphere (~15 to~95km) from ~60°N to the pole from its surroundings. While the breaking (as in oceanic ‘surf’) of large-scale waves, associated with the longitudinal structure of the weather patterns at middle latitudes, is consistent with the meridional winds and vertical structure of the vortex in the stratosphere, the large continents of the Northern Hemisphere (NH) lead to longitudinal thermal and dynamical asymmetries; the resulting largest planetary-scale waves in turn distort the shape and location of the Arctic Vortex (Xu et al., 2009; Manson et al., 2008; Chshyolkova et al., 2007). From December, the vortex-edge and even centre often slides into the Scandinavian-Atlantic sectors; the Canadian Eastern Arctic, including Eureka, may thus be inside or outside of the vortex, especially during Sudden Stratospheric Warmings (SSW) (Lindenmaier et al., 2012; Chshyolkova et al., 2007) that may cause complete breakdown (Major Stratospheric Warming, MSW) of the vortex. Ozone, within the stratosphere of a displaced vortex, may be destroyed during the coldest days of winter (Lindenmaier et al., 2012; Kvissel et al., 2012) when there is local sunlight, unless regional or MSWs (Manson et al., 2008) protect the ozone from depletion until the spring (Manney et al., 2011). Smaller-scale waves, so-called Gravity Waves (GW), are also intrinsically involved within the vortex and undergo large changes in flux during the SSW (Becker and Fritts, 2006, Limpasuvan et al., 2011). The greater symmetry of Antarctica leads to a vortex that seldom experiences such disturbances. The summer westward circulation of the NH is less energetic, and is coupled to the Antarctic southern polar vortex (Xu et al., 2009; Becker and Fritts, 2006; Limpasuvan et al., 2011) by way of southward flows from the Arctic mesosphere. The variability of the extension of the polar vortex above the stratopause (55-60km) (Xu et al., 2009; Chshyolkova et al., 2007) is thus also relevant to this Proposal; studies of the ‘upper branch’ of the vortex are also included in the International CAWSES-II (Climate And Weather of the Sun-Earth System) Program and will be related to future SCOSTEP (Scientific Committee on Solar-Terrestrial Physics) programs.

The coupling between the Arctic troposphere and stratosphere, or the coherent extension of the Arctic vortex into the troposphere, is also of great importance and complexity; studies continue and understanding improves (Kolstad and Charlton-Perez, 2011; Kolstad et al., 2010; Alexander and Shepherd, 2010; Hardiman et al., 2011). In recent early winters (Dec-Jan) the outbreaks of frigid Arctic air [due to lower vortex-breakdown] to middle latitudes of Russia, Europe and Canada-US, raises concern and scientific engagement (Kolstad et al., 2010; Seager et al., 2010); variations of radiation-budgets, related to diminishing ice-coverage in the Arctic Ocean, are occurring. The other manifestations of Arctic variability are the internal breakdowns (SSW, MSW) or vortex changes associated with equatorial-subtropical systems: Quasi-Biennial Oscillation (QBO) (Seager et al., 2010; Inoue et al., 2011; Lu and Jarvis, 2011; Anstey and Shepherd, 2008; Xu et al., 2011a), El Nino Southern Oscillation (ENSO)(Seager et al., 2010; Ren et al., 2012; Lin et al., 2010), the North Atlantic Oscillation (NAO) (Seager et al., 2010; Lin et al., 2010; Hurrell and van Loon, 1997; Baldwin and Dunkerton, 1999; Cohen et al., 2010), and chemicals as tracers, and ozone loss (Lindenmaier et al., 2012; Kvissel et al., 2012; Manney et al., 2011; Verronen et al., 2011). Solar cycles also affect the occurrence of the SSW and equatorial systems (Lu and Jarvis, 2011; Labitzke et al., 2006; Labitzke et al., 2008). Improved understanding of these coupling processes, as well as placing lower atmospheric measurements made from PEARL in better physical context, is an inherent objective; it provides the pathway to improved weather forecasts, at longer time scales (weeks, months to interannual; e.g., Kolstad and Charlton-Perez, 2011; Kolstad et al., 2010; Hardiman et al., 2011; Seager et al., 2010; Lin et al., 2010).