Assessing the Impacts of Arctic Amplification on the Midlatitude Circulation with a Hierarchy of Atmospheric General Circulation Models

Arctic amplification refers to the tendency of the high latitudes of the Northern Hemisphere to warm faster than the rest of the globe. This effect has been documented both in the warming trends of recent decades and in climate model simulations of greenhouse gas-induced climate change, and is closely related to the decline of Arctic sea ice and reductions in Fall snow cover over northern Eurasia.

This project addresses the potential for Arctic amplification to influence the weather and atmospheric circulation of the middle latitudes of the Northern Hemisphere. Motivation for the work comes from recent simulations which suggest that reductions in Arctic sea ice in late Summer and early Fall promotes the negative phase of the Northern Annular Mode, in which sea level pressure is high over the Arctic and the Northern Hemisphere jet streams and storm tracks are shifted southward. Further motivation comes from recent claims that Arctic amplification has resulted in an increase in the frequency of atmospheric blocking events, which are associated with extreme weather events including the cold air outbreaks over the US during the winter of 2013/2014 as well as recent summer heat waves over Europe.

The research examines the effect of Arctic amplification on atmospheric circulation, including jet streams, storm tracks, and blocking events, using a hierarchy of models of varying levels of complexity. In this modeling approach, the simplest models are used to isolate and study the fundamental dynamical mechanisms responsible for the behaviors found in more complex and realistic simulations. A key concern of the research is that Arctic amplification will act in concert with other consequences of global warming, including the warming of tropical upper troposphere, and previous work suggests that the warming of the tropical upper troposphere leads to a poleward shift of jets and storm tracks which will somewhat offset the impact of Arctic amplification. A second concern is the possible role of the stratosphere in mediating connections between the Arctic and the midlatitude circulation. Previous work shows that circulation changes at stratospheric levels over the polar cap can influence midlatitude weather, and that these influences can propagate slowly downward, resulting in time lags up to a few months between high-latitude forcing and midlatitude response.

As noted above, the topic of this research has societal broader impacts due to the potential for Arctic amplification to produce changes in the weather patterns of the Northern Hemisphere midlatitudes, in particular over the populous regions of the US and Europe. Even subtle shifts of jet streams and storm tracks can yield significant changes in rainfall and available water resources, and blocking events are an important source of extreme winter cold and summer heat waves. The research conducted here may be of value for both long-term climate projections and near-term weather forecasting.