Wavelet Analysis of the Polar Vortex and Linkages to Climate Change

Extreme weather events have been linked to unusually amplified atmospheric waves (Screen and Simmons, Nature Clim. Change, 2014). Changes in Rossby wave properties may be linked to changes in climate; hence, an increase in the frequency of extreme weather events may be an indication of a large-scale change in wave properties and thereby large scale climatic changes. Arctic amplification and the related ice-albedo feedback mechanism make this issue more pressing in the polar north, where the rate and magnitude of climate change has been most pronounced (Serreze et al, The Cryosphere, 2009). While there is debate over whether a tipping point will be reached (Tietsche et al, GRL, 2011), dramatic change would be difficult to slow or stop should that occur. In this study, wavelet analysis is applied to time series of zonal phase speeds of Rossby waves at high latitudes. A strong annual signal is found; this signal has tended to increase in power since approximately 1940. It is demonstrated that signals at larger time scales at these latitudes are more isolated, although there may be a westerly propagation pattern. Significant correlations between wavelet power and albedo, snow cover, atmospheric ozone levels, and surface temperature are found at shorter scales. At longer scales there is more ambiguity, but significant correlations with those factors and carbon dioxide levels seem likely. The analysis suggests that patterns of Rossby wave speeds have undergone considerable intensification since 1940. This intensification may have a link to the ice-albedo feedback mechanism, potentially hastening a tipping point in the retreat of the cryosphere.