Recurrent Synoptic-Scale Rossby Wave Patterns and Their Effect on the Persistence of Cold and Hot Spells

Abstract

The persistence of surface weather during several recent high-impact weather events has been pivotal in generating their societal impact. Here we examine Hovmöller diagrams of the 250-hPa meridional wind during several periods with particularly persistent surface weather and find a common pattern in these Hovmöller diagrams. This pattern can be characterized as a “recurrent Rossby wave pattern” (RRWP), arising from multiple transient synoptic-scale wave packets. During such RRWP periods, individual troughs and ridges forming the wave packets repeatedly amplify in the same geographical region. We discuss the synoptic evolution of two RRWP periods, in February–March 1987 and July–August 1994, and illustrate how the recurrence of the transient wave packets led to unusually long-lasting cold and hot spells, which occurred simultaneously in several regions, each separated by roughly one synoptic wavelength. Furthermore, a simple index termed R is proposed to identify RRWPs, which is based on both a time and wavenumber filter applied to conventional Hovmöller diagrams. A Weibull regression analysis then shows that large values of R are statistically significantly linked to increased durations of winter cold and summer hot spells in large areas of the Northern Hemisphere midlatitudes. Traditionally, persistent high-impact surface weather has often been linked to the occurrence of proximate atmospheric blocking. In contrast to blocking, RRWPs affect persistent surface temperature anomalies over multiple synoptic wavelengths. We therefore argue that, in addition to blocking, RRWPs should be considered as an important flow feature leading to persistent high-impact surface weather.

Quantifying the Local Effect of Northern Hemisphere Atmospheric Blocks on the Persistence of Summer Hot and Dry Spells

“…These regions can thus be considered as hot spots for long‐lasting compound hot and dry spells associated with blocking. Interestingly, western North America and central Europe are also areas where recurrent Rossby wave patterns (RRWPs) foster particularly long‐lasting summer hot spells (Röthlisberger et al, ). These areas might thus be particularly prone to persistent heat induced by both blocks and RRWPs.…”

“…However, also synoptic to hemispheric-scale atmospheric circulation patterns play a pivotal role in generating long-lasting heat waves and droughts. Recent studies have therefore investigated the atmospheric dynamics mechanisms leading to persistent hot surface weather for several recent examples of extremely long-lasting heat waves (Barriopedro et al, 2011;Black et al, 2004;Dole et al, 2011;Fink et al, 2004;Parker et al, 2014;Schneidereit et al, 2012;Xu et al, 2019;Zschenderlein et al, 2018) as well as from a climatological point of view (Kornhuber et al, 2017;Röthlisberger et al, 2019).…”

Dynamics of concurrent and sequential Central European and Scandinavian heatwaves

“…(2018) showed that in southern Europe narrow subtropical ridges rather than blocking lead to extremely warm conditions. Rossby‐wave packets (Fragkoulidis et al ., 2018), recurrent (Röthlisberger et al ., 2019) or stationary (Kornhuber et al ., 2019) Rossby waves have also been linked to high temperature extremes. Further, Drouard and Woollings (2018) revealed a regional dependence of the formation and maintenance mechanisms of blocking and their connection to the North Atlantic storm track.…”

Potential-Vorticity Dynamics of Troughs and Ridges within Rossby Wave Packets during a 40-year reanalysis period

“…Specifically, RWPs organize the formation, intensification, and movement of weather systems and special attention has been given to RWPs as precursors to extreme weather events (e.g., Shapiro and Thorpe, 2004;Martius et al, 2008;Wirth and Eichhorn, 2014;Piaget et al, 2015;Grazzini et al, 2020). Beyond individual weather systems, the recurrent occurrence of RWPs has been associated with periods of temperature extremes (Röthlisberger et al, 2019). And from a climatological perspective, the dynamics of midlatitude storm tracks can be described in terms of the excitation, propagation, and decay of RWPs (Chang and Orlanski, 1993;Chang et al, 2002).…”