Defining Sudden Stratospheric Warmings

Abstract

Sudden stratospheric warmings (SSWs) are large, rapid temperature rises in the winter polar stratosphere, occurring predominantly in the Northern Hemisphere. Major SSWs are also associated with a reversal of the climatological westerly zonal-mean zonal winds. Circulation anomalies associated with SSWs can descend into the troposphere with substantial surface weather impacts, such as wintertime extreme cold air outbreaks. After their discovery in 1952, SSWs were classified by the World Meteorological Organization. An examination of literature suggests that a single, original reference for an exact definition of SSWs is elusive, but in many references a definition involves the reversal of the meridional temperature gradient and, for major warmings, the reversal of the zonal circulation poleward of 60° latitude at 10 hPa. Though versions of this definition are still commonly used to detect SSWs, the details of the definition and its implementation remain ambiguous. In addition, other SSW definitions have been used in the last few decades, resulting in inconsistent classification of SSW events. We seek to answer the questions: How has the SSW definition changed, and how sensitive is the detection of SSWs to the definition used? For what kind of analysis is a “standard” definition useful? We argue that a standard SSW definition is necessary for maintaining a consistent and robust metric to assess polar stratospheric wintertime variability in climate models and other statistical applications. To provide a basis for, and to encourage participation in, a communitywide discussion currently underway, we explore what criteria are important for a standard definition and propose possible ways to update the definition.

Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings

“…A classification of SSWs can also be found in Chandran et al (2014), including their type. Of course, the classification of SSWs into major and minor SSWs somewhat depends on the data, as well as on the criterion used (e.g., Charlton and Polvani, 2007;Butler et al, 2015).…”

Impact of the 2009 major sudden stratospheric warming on the composition of the stratosphere

“…The definitions for SSW and classifications are extensively discussed by Butler et al (2015). According to commonly used criteria (Christiansen, 2001;Charlton and Polvani, 2007), we identify the warming event on 24 January by the reversal of 60 • N westerly zonal-mean wind at 10 hPa.…”

Residual Mean Circulation and Temperature Changes during the Evolution of Stratospheric Sudden Warming Revealed in MERRA

“…Various definitions of SSW have been suggested recently (Butler et al, 2015). According to Charlton and Polvani (2007) (hereafter CP07), one of the most commonly used definitions, SSW occurs when zonal-mean zonal wind at 60° N and 30 2 SSW events have usually been classified into two types according to changes in the polar vortex structure during the evolution of SSW events (Yoden et al, 1999;Ryoo and Chun, 2005;CP07).…”