Bulletin of the American Meteorological Soceity, in press.
Darryn W. Waugh
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD.
Adam H. Sobel and Lorenzo M. Polvani
Department of Applied Physics and Applied Mathematics and Lamont-Doherty Earth Observatory, Columbia University, New York, NY.
The term “polar vortex” has become part of the everyday vocabulary, but there is some confusion in the media, general public, and science community regarding what polar vortices are and how they are related to various weather events. Here we clarify what is meant by polar vortices in the atmospheric science literature. It is important to recognize the existence of two separate planetary-scale circumpolar vortices: one in the stratosphere and the other troposphere. These vortices have different structure, seasonality, dynamics, and impacts on extreme weather. The tropospheric vortex is much larger than its stratospheric counterpart and exists year-round, whereas the stratospheric polar vortex forms in fall but disappears in the spring of each year. Both vortices can, in some circumstances, play a role in extreme weather events at the surface, such as cold air outbreaks, but these events are not the consequence of either the existence or gross properties of these two vortices. Rather, cold air outbreaks are most directly related to transient, localized displacements of the edge of the tropospheric polar vortex which may, in some circumstances, be related to the stratospheric polar vortex: but there is no known one-to-one connection between these phenomena.