Abstract

Over recent decades the Arctic has warmed about three times as much as the global average, a phenomenon known as Arctic amplification (AA). There has been much interest in the extent to which AA can influence mid-latitude climate, with some studies suggesting that it may drive more frequent or long-lived weather extremes. However, general circulation models (GCMs) simulate widely diverging responses to polar heating, both in the mean atmospheric circulation and its variability. In this talk I will present two examples of recent work from my group, in which an idealised model, Isca, helps to explain some of the causes of this uncertainty. In the first, I will discuss the response of the persistence of surface temperature anomalies to AA. I will show that this response is large but absent in most GCM experiments due to the method by which they remove sea-ice. The persistence response is largest in the Arctic, but extends to mid-latitudes, where it is dynamically-driven, caused by a slowing of meridional wind anomalies. In the second example, I will discuss the ‘stratospheric pathway’, by which AA may dynamically impact lower latitudes. I will show that, by varying a single parameter that controls the mean strength of the stratospheric polar vortex, a range of stratospheric responses (both a strengthening and a weakening of the polar vortex) can be obtained, similar to the range seen in GCMs. These range of stratospheric responses, in turn, significantly impact the magnitude of the shift of the eddy-driven jet.