Warm Season Subseasonal Variability and Climate Extremes in the Northern Hemisphere: The Role of Stationary Rossby Waves

Abstract

This study examines the nature of boreal summer subseasonal atmospheric variability based on the new NASA Modern-Era Retrospective analysis for Research and Applications (MERRA) for the period 1979-2010. An analysis of the June, July and August subseasonal 250hPa v-wind anomalies shows distinct Rossby wave-like structures that appear to be guided by the mean jets.On monthly subseasonal time scales, the leading waves (the first 10 rotated empirical orthogonal functions or REOFs of the 250hPa v-wind) explain about 50% of the Northern Hemisphere vwind variability, and account for more than 30% (60%) of the precipitation (surface temperature) variability over a number of regions of the northern middle and high latitudes, including the U.S.northern Great Plains, parts of Canada, Europe, and Russia. The first REOF in particular, consists of a Rossby wave that extends across northern Eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability, and played an important role in the 2003 European and 2010 Russian heat waves. While primarily subseasonal in nature, the Rossby waves can at times have a substantial seasonal mean component. This is exemplified by REOF 4 which played a major role in the development of the most intense anomalies of the U.S. 1988 drought (during June) and the 1993 flooding (during July), though differed in the latter event by also making an important contribution to the seasonal mean anomalies. A stationary wave model (SWM) is used to reproduce some of the basic features of the observed waves and provide insight into the nature of the forcing. In particular, the responses to a set of idealized forcing functions are used to map the optimal forcing patterns of the leading waves. Also, experiments to reproduce the observed waves with the SWM using MERRA-based estimates of the forcing indicate that the wave forcing is dominated by sub-monthly vorticity transients.

The Asian–Bering–North American teleconnection: seasonality, maintenance, and climate impact on North America

“…Thus North American winter temperature is mostly controlled by these three atmospheric teleconnection patterns. It is noted that stationary Rossby waves, which play an important role in interannual variability of the teleconnections spanning from Eurasia to North America, are observed not only in winter but also in summer (e.g., Schubert et al 2011;Ding et al 2011;Wu et al 2009. Therefore, this study extends our previous analysis by characterizing the seasonality of the ABNA pattern.…”

Quasiresonant amplification of planetary waves and recent Northern Hemisphere weather extremes

“…In the meantime, several other unusually strong regional summer extremes already have occurred in recent years that make it questionable that only a purely stochastic mechanism of extremes is at work (8). The global observations attest that these extremes, such as the Russian heat wave in 2010 and the record heat wave in the United States in 2011, persisted over nearly the whole summer-which is not inherent in ordinary blockings with a characteristic e-folding time of about 5-7 d-and were in fact of hemispheric scale: a stable anomalous atmospheric circulation pattern enveloped the whole NH (4,(9)(10)(11)(12)(13)(14).…”

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

“…was subsequently applied to explain several important features of some of the recent summer extremes (18)(19)(20)(21)27 Petoukhov et al (34) proposed a common mechanism for generating persistent high-amplitude quasibarotropic planetaryscale wave patterns of the NH midlatitude atmospheric circulation with zonal wave numbers m = 6, 7, and 8 that can explain a number of the major NH summer extremes over the 1980-2011 period (34,35). Petoukhov et al (34) showed that these patterns could result from the trapping of free quasistationary barotropic Rossby waves with zonal wave numbers k equal or close to the three integer values indicated above, within the predominantly zonally oriented midlatitude waveguides.…”

“…However, a number of severe summer extremes have already occurred since then in the NH, particularly in Europe. The anomalous atmospheric circulation patterns accompanying these extremes were of hemispheric scale (14)(15)(16)(17)(18)(19)(20)(21)(22). They encircled the entire NH and persisted over nearly the whole summer, which is fundamentally different from conventional regional blocking events with about a 10-d life span (23).…”