What Is the Polar Vortex and How Does It Influence Weather?

T he term polar vortex has become part of the everyday vocabulary after the widespread media coverage of the extreme cold events over the United States during the early winter of 2014. However, there is some confusion in the media, general public, and even within the science community regarding what polar vortices are and how they are related to various weather events. This confusion is illustrated by the fact that the polar vortex entry in the American Meteorological Society (AMS) glossary was revised in 2000, 2014, and again in October 2015 (AMS 2015). Much of the confusion stems from the fact that polar vortex is used in the literature to explain two different features of the atmospheric circulation: one in the troposphere and the other in the stratosphere. The distinction between them is not always made clear in discussions of extreme cold events. Another source of confusion stems from the fact that these polar vortices are neither unusual nor extreme; they are simply basic features of Earth’s climatology. While some extreme weather events at some locations are related to transient displacements of the edge of the tropospheric polar vortex, these events are in no way a manifestation of major changes in the global atmospheric circulation. Here, we clarify the different structures, seasonality, and dynamics of the stratospheric and tropospheric polar vortices and discuss the connections of both to extreme weather events at Earth’s surface.