Persistent Extratropical Regimes and Climate Extremes

Abstract

Some studies have suggested a recent increase in high-impact persistent circulation regimes in the extratropics. In this brief review paper, we discuss some aspects of this work and also consider more broadly how regimes such as blocking and stationary Rossby wave patterns may be altered under climate change. The amplified Arctic warming is discussed as one of several factors influencing the atmospheric dynamics from the equator to the poles. Some theoretical arguments are given alongside discussion of observational and modelling results. We include consideration of climate model skill and statistical aspects of the problem linking the distribution of climate variables to the extremes.

Role of quasiresonant planetary wave dynamics in recent boreal spring-to-autumn extreme events

“…This attests that the QRA, as described here in a quasilinear approximation, is not, of course, the only mechanism for generating regimes of high-amplitude midlatitude waves with m = 6, 7, and 8. Other important competing mechanisms exist that can drive highamplitude midlatitude extratropical planetary waves, like the Branstator mechanism (26), El Niño−Southern Oscillation (51), and North Atlantic Oscillation (NAO) (37). The choice of the mean flow and the scale separation between the mean flow and the stationary waves is critical.…”

A Review of Recent Advances in Research on Extreme Heat Events

“…This suggests that warming could lead to more diabatic heating within moister air, bringing stronger blocks thereafter [35]. However, Hoskins and Woollings [40] hypothesize that because blocking is favored downstream from storm tracks (e.g., [41]), and a weakening equator-to-pole temperature gradient can mean weaker storm tracks [23], downstream blocking could decrease in a future climate [42]. CMIP3 and CMIP5 models generally project fewer blocking events in the future, although Hoskins and Woolings note that midlatitude blocking could change due to a feature not captured by general circulation models (GCMs), such as changes in tropical forcing [40].…”

“…However, Hoskins and Woollings [40] hypothesize that because blocking is favored downstream from storm tracks (e.g., [41]), and a weakening equator-to-pole temperature gradient can mean weaker storm tracks [23], downstream blocking could decrease in a future climate [42]. CMIP3 and CMIP5 models generally project fewer blocking events in the future, although Hoskins and Woolings note that midlatitude blocking could change due to a feature not captured by general circulation models (GCMs), such as changes in tropical forcing [40]. It remains that the theoretical basis for future changes in blocking variability is not established and the scientific debate surrounding blocking is emblematic of debates about future changes in midlatitude circulation more generally.…”

Extreme drought in the recent two decades in northern China resulting from Eurasian warming

“…Previous studies suggest that Eurasian droughts are strongly linked to the development of blocking and stationary Rossby waves (e.g., Scaife et al 2010;Schubert et al 2014). Specifically, the stationary wave anomaly is an important component of Eurasian temperature and rainfall variability in summer, associated with wave propagation patterns (Ambrizzi et al 1995;Hoskins and Woollings 2015), such as the wave anomaly related to the European heat wave in 2003 and Russian heat wave in 2010 (Schubert et al 2014). Therefore, stationary wave anomaly is worth exploration, because it will lead to amplitude, E-W location and N-S location change of stationary wave.…”