Observed and simulated precursors of stratospheric polar vortex anomalies in the Northern Hemisphere

Abstract

The Northern Hemisphere stratospheric polar vortex is linked to surface weather. After Stratospheric Sudden Warmings in winter, the tropospheric circulation is often nudged towards the negative phase of the Northern Annular Mode (NAM) and the North Atlantic Oscillation (NAO). A strong stratospheric vortex is often associated with subsequent positive NAM/NAO conditions. For stratosphere-troposphere associations to be useful for forecasting purposes it is crucial that changes to the stratospheric vortex can be understood and predicted. Recent studies have proposed that there exist tropospheric precursors to anomalous vortex events in the stratosphere and that these precursors may be understood by considering the relationship between stationary wave patterns and regional variability. Another important factor is the extent to which the inherent variability of the stratosphere in an atmospheric model influences its ability to simulate stratosphere-troposphere links. Here we examine the lower stratosphere variability in 300-year pre-industrial control integrations from 13 coupled climate models. We show that robust precursors to stratospheric polar vortex anomalies are evident across the multi-model ensemble. The most significant tropospheric component of these precursors consists of a height anomaly dipole across northern Eurasia and large anomalies in upward stationary wave fluxes in the lower stratosphere over the continent. The strength of the stratospheric variability in the models was found to depend on the variability of the upward stationary wave fluxes and the amplitude of the stationary waves.

On the Predictability of the Winter Euro-Atlantic Climate: Lagged Influence of Autumn Arctic Sea Ice

“…8c), once the negative NAO is established (Figs. 3b and 4b propagation of planetary waves (Kuroda and Kodera 1999;Garfinkel et al 2010;Kolstad and Charlton-Perez 2011), producing circulation anomalies in the stratospheric polar vortex that subsequently descend to the troposphere and project on the NAO (e.g., Polvani and Waugh 2004). Different mechanisms have been proposed to explain this downward propagation of anomalies (see Gerber et al 2012;Tomassini et al 2012 for review).…”

“…When tropospheric anomalies reinforce (i.e., are in phase with) the climatological wave pattern, wave driving of the polar vortex is expected to increase, and conversely when the tropospheric anomalies are out of phase with the climatological wave pattern (Garfinkel et al 2010;Kolstad and Charlton-Perez 2011). Climatological planetary waves are enhanced by a low over the eastern Eurasian sector, where the climatological wavenumber 1 and wavenumber 2 are both low, and by a high over the western Eurasian sector, where climatological wavenumber 1 and wavenumber 2 are both high (Garfinkel et al 2010).…”

“…9b, contours) constructively interferes with the climatological wave pattern over Eurasia. This enhancement in amplitude would lead to amplified meridional heat fluxes, thereby increasing the upward propagation of wave activity into the stratosphere (Kolstad and Charlton-Perez 2011). The spatial distribution of November y*T* depicts the key regions in the tropospheric wave driving of the stratospheric polar vortex.…”

A comparative study of the major sudden stratospheric warmings in the Arctic winters 2003/2004–2009/2010

“…Bancalá et al, 2012;Butler and Polvani, 2011;Cohen and Jones, 2011;Kolstad and Charlton-Perez, 2011;Manney et al, 2009;Charney and Drazin, 1961). The MW periods normally preceded by high wave activity at the tropopause, in which more than one planetary wave (generally waves 1 and 2) will be present.…”

The Relevance of the Location of Blocking Highs for Stratospheric Variability in a Changing Climate

“…Blocking highs (BHs) constitute one of the clearest examples of tropospheric precursors of wintertime polar stratospheric variability (e.g., Martius et al 2009;Kolstad and Charlton-Perez 2011). They consist of anticyclonic quasi-stationary anomalies in the tropospheric pressure field that persist for several days to weeks, obstructing the westerly winds and midlatitude weather systems (Rex 1950).…”