Absorbing and reflecting sudden stratospheric warming events and their relationship with tropospheric circulation

Abstract

Sudden stratospheric warming (SSW) events have received increased attention since their impacts on the troposphere became evident recently. Studies of SSW usually focus on polar stratospheric conditions; however, understanding the global impact of these events requires studying them from a wider perspective. Case studies are used to clarify the characteristics of the stratosphere-troposphere dynamical coupling, and the meridional extent of the phenomena associated with SSW. Results show that differences in the recovery phase can be used to classify SSW events into two types. The first is the absorbing type of SSW, which has a longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere. The absorbing type of SSW is related to the annular mode on the surface through poleward and downward migration of the deceleration region of the polar night jet. The other is the reflecting type. This is characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves inducing strong westerlies over the North Atlantic and blocking over the North Pacific sector. Differences in the tropospheric impact of the absorbing and reflecting SSWs are also confirmed with composite analysis of 22 major SSWs.

Observed and Simulated Teleconnections Between the Stratospheric Quasi‐Biennial Oscillation and Northern Hemisphere Winter Atmospheric Circulation

“…Connections between the AO/NAO and the stratosphere in wintertime are a two‐way interaction. The stratospheric polar vortex responds to tropospheric weather patterns via rapid upward planetary wave propagation (on a timescale of a day or two; e.g., Kodera et al, ). Changes in the stratospheric vortex, meanwhile, produce a slower downward influence (days to weeks; Baldwin & Dunkerton, ) that affects surface weather patterns, influencing the AO and NAO (Kidston et al, ).…”

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

“…It has been found that the circulation anomalies of SSWs have influence on surface weather and climate (e.g., Baldwin and Dunkerton, 2001;Kodera et al, 2016), as well as on sea surface temperature (O'Callaghan et al, 2014). Near-surface effects of SSWs are not limited to the polar region, but can also extend to low latitudes (e.g., Hitchcock and Simpson, 2014).…”

Stratospheric tropical warming event and its impact on the polar and tropical troposphere

“…Such a change in the wave structure is similar to that observed following planetary wave reflection events (Shaw and Perlwitz, 2013;Kodera et al, 2008Kodera et al, , 2013, although the pattern was somewhat shifted eastward in the present case. In the usual case, an initial change in the zonal-mean zonal wind field in the stratosphere is created by a stronger upward propagation of planetary waves from the troposphere (Kodera et al, 2016a). In the present case, reflection occurred without the preceding enhanced upward propagation of planetary waves from the troposphere, but it was attributed to the deflection of waves in the upper stratosphere by MASTJ.…”

“…The influence of downward penetration of zonal winds from the polar stratosphere, such as the annular modes (Baldwin and Dunkerton, 1999;Thompson and Wallace, 2001) or the polar night jet (PNJ) oscillation (PJO) Kodera, 1999, 2004;Hitchcock et al, 2013), has been well documented. More recently, the connection between tropospheric weather and changes in planetary wave structure in the polar region, due to reflection or downward propagation in the polar region, has also been reported (Perlwitz and Harnik, 2003;Shaw and Perlwitz, 2013;Kodera et al, 2008Kodera et al, , 2013Kodera et al, , 2016a. Although stratosphere-troposphere coupling in the tropical region is more controversial, a possible connection has been proposed based on the modulation of deep convective activity by the stratospheric quasi-biennial oscillation (QBO) (Collimore et al, 2003;Liess and Geller, 2012;Yoo and Son, 2016) and sudden stratospheric warming (SSW) (Kodera, 2006;Eguchi and Kodera, 2010;Kodera et al, 2015;Eguchi et al, 2016).…”