Dynamics of Arctic-Midlatitude Teleconnections: mechanisms, robustness and tropical modulation

Global warming has accelerated in the last decade. Nowhere is this more apparent than in the Arctic, where rising temperatures and shrinking sea ice cover have garnered much media attention. These Arctic changes could have important impacts away from the Arctic as well, and these are less well understood. One pressing question is whether Arctic warming has altered midlatitude weather patterns, increasing the likelihood of extreme events such as persistent cold snaps, droughts, floods and heat waves in some of the most highly populated regions of the world. Though there are many theories for Arctic-midlatitude linkages, there is as of yet no consensus. And while Arctic warming could be one driver of changes in midlatitude weather, there is strong evidence that the stratosphere and tropical variability also play important roles. DynAMiTe will explore the dynamical origins of Arctic-midlatitude teleconnections, aiming to challenge and clarify the role of the Arctic in determining regional climate variability. It will achieve this goal using observations, comprehensive climate model simulations, and experiments using a hierarchy of simplified dynamical models. The integrated framework is grounded in fundamental dynamics but exploits high-resolution reanalysis data sets and large ensemble climate model output that have only become available in recent years. We expect DynAMiTe to yield new insight into Arctic-midlatitude teleconnections, which in turn will help resolve confusing messages about the topic in mainstream media. Results from the project: - In climate models, subpolar atmosphere-ocean interactions appear to contribute to how much Arctic amplification of warming is simulated. - Linkages between Arctic sea ice and North Atlantic climate can be identified in observations, but they are intermittent. The dynamical pathway seems to be active only under special conditions, both in climate models and the real world. - ENSO teleconnections from the tropical Pacific to the Euro-Atlantic sector evolve through the year, and appear to be most robust in autumn. - The large-scale flow over the North Atlantic more than sea ice extent is most important for determining the path of moisture-laden cyclones to the Arctic. - Estimates of future changes in ENSO teleconnections are highly uncertain due to the presence of atmospheric internal variability.

The project has contributed meaningfully to clarifying the characteristics and origins of Arctic-midlatitude teleconnections, including: the important role of internal atmospheric variability in modulating linkages from the Arctic to the midlatitudes; the possibility of reducing uncertainty in teleconnections from the tropical Pacific to the North Atlantic by accounting for the evolution of the teleconnections from late autumn to late winter; clarifying atmospheric and oceanic mechanisms of energy transport that affect Arctic surface climate; clarifying the role of the stratospheric pathway in Arctic teleconnections; enhancing collaboration across partner institutions of the Bjerknes Center for Climate Research, with other national research institutions, and with leading research institutions in the US, Canada and UK.

DynAMiTe takes a dynamics-based approach to answer one of the most pressing questions in climate science today: Is the rapidly changing climate in the Arctic altering midlatitude atmospheric circulation? The answer to this question is essential for understanding both year-to-year variations in regional climate and weather extremes, and projecting how these will change in a warming world. Though there are many theories for how Arctic-midlatitude teleconnections operate, there is as of yet no consensus. Many of the proposed mechanisms point to Arctic Amplification (AA) of global warming as a driver of the midlatitude changes, but there is strong evidence that the stratosphere and tropical variability also play important roles. An ongoing challenge is identifying robust, physical pathways by which the AA can affect the midlatitude circulation, and evaluating their importance relative to other influences on the midlatitudes. This innovative collaboration will explore the dynamical origins of Arctic-midlatitude teleconnections by combining key and complementary expertise from the University of Bergen and Uni Climate with international partners at the Lamont-Doherty Earth Observatory at Columbia University (USA), the National Center for Atmospheric Research (USA) and the University of Toronto (Canada). The central goal of the collaboration is to challenge and clarify the role of AA in determining regional climate variability by combining new analyses of comprehensive climate model simulations and observations with experiments using a hierarchy of simplified dynamical models. The integrated framework is grounded in fundamental dynamics but exploits high-resolution reanalysis data sets and large ensemble climate model output that have only become available in recent years. We expect DynAMiTe to yield new insight into Arctic-midlatitude teleconnections, which in turn will help resolve confusing messages about the topic in mainstream media.