Suppressed eddy driving during southward excursions of the North Atlantic jet on synoptic to seasonal time scales

• Published in: Atmospheric science letters Vol. 20; no. 9
• Main Authors: Madonna, Erica, Li, Camille, Wettstein, Justin J.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-09-2019; John Wiley & Sons, Inc; Wiley
• Subjects: Atmospheric sciences; Bridges; Climate; Climate models; Climate variability; Computer simulation; eddy‐mean flow interactions; Heating; Induction heating; Jet stream; Jet streams (meteorology); North Atlantic; Ocean currents; Regional climate models; Regional climates; Seasons; Time; Tropical climate; Variability; Weather; Winter
• ISSN: 1530-261X; 1530-261X
• DOI: 10.1002/asl.937

Jet streams shape midlatitude weather and climate. The North Atlantic jet is mainly eddy‐driven, with frequent north–south excursions on synoptic time scales arising from eddy forcings and feedbacks. There are, however, special periods during which the underlying dynamics appear to change—for example, winter 2009/2010, when the jet was persistently southward‐shifted, extremely zonal, and more thermally driven. This study shows evidence that the southern jet configuration exhibits altered dynamical behavior involving a shift in the balance of thermal and eddy‐driving processes, independent of timescale. Specifically, southern jets exhibit weaker eddy feedbacks and are associated with enhanced heating in the tropical Pacific. During winter 2009/2010, a remarkably frequent (66 days out of the 90‐day winter season) and persistent southern jet shaped the unusual seasonal signature. These results bridge the synoptic and climate perspectives of jet variability, with potential to help understand and reduce biases in regional climate variability as simulated by models.
Southward excursions of the North Atlantic jet (contours) on weather to climate time scales reflect altered dynamical behavior, with weaker eddy driving (locally) and enhanced thermal driving from convective heating in the tropical Pacific. Special seasonal signatures like the southward‐shifted jet of winter 2009/2010 can be seen as the result of an unusually high occurrence of “typical” synoptic southern jets.