Abstract
The El Niño–Southern Oscillation (ENSO) is a major driver of Northern Hemisphere wintertime variability and, generally, the key ingredient used in seasonal forecasts of wintertime surface climate. Modeling studies have recently suggested that ENSO teleconnections might involve both a tropospheric pathway and a stratospheric one. Here, using reanalysis data, we carefully distinguish between the two. We first note that the temperature and circulation anomalies associated with the tropospheric pathway are nearly equal and opposite during the warm (El Niño) and cold (La Niña) phases of ENSO, whereas those associated with the stratospheric pathway are of the same sign, irrespective of the ENSO phase. We then exploit this fact to isolate the two pathways. Our decomposition reveals that ENSOs climate impacts over North America are largely associated with the tropospheric pathway, whereas ENSOs climate impacts over the North Atlantic and Eurasia are greatly affected by the stratospheric pathway. The stratospheric pathway, which we here define on the basis of the occurrence of one or more sudden stratospheric warmings in a given winter, and whose signature projects very strongly on the North Atlantic Oscillation, is found to be present 60% of the time during ENSO winters (of either phase): it therefore likely plays an important role in improving seasonal forecasts, notably over the North Atlantic and the Eurasian continent.
Highlights
The geopotential height anomalies following stratospheric warmings (SSWs) closely resemble the negative phase of the North Atlantic Oscillation (NAO) (Baldwin and Dunkerton 2001), with positive heights over Greenland and the Arctic, and negative heights over the North Atlantic and extending across Europe; we note significant positive heights over subtropical Asia
The temperature patterns following SSWs (figure 2(a), top panel) likewise resemble what is typically seen in a negative NAO phase, with cold anomalies over northern Europe, Asia, and the eastern United States, and warm anomalies over eastern Canada and parts of Greenland, and over much of China, the Middle East, and North Africa
We have demonstrated that the presence—or absence—of the stratospheric pathway during El Nino–Southern Oscillation (ENSO) winters makes a very significant difference in the surface climate response over large portions of the Arctic, North Atlantic and Eurasia
Summary
Horel and Wallace (1981) showed that ENSO teleconnections resemble tropospheric Rossby wave trains forced in the tropical Pacific Ocean by slowly evolving anomalous sea surface temperatures (SSTs) via changes in precipitation. Many ENSO induced climate anomalies are, to first order, linear in character, 1748-9326/14/024014+09$33.00 c 2014 IOP Publishing Ltd Printed in the UK. Over the Pacific and North American sectors, ENSO impacts can be largely accounted for with linear wave theory and simple ray tracing in the troposphere (Hoskins and Karoly 1981, Horel and Wallace 1981, Sardeshmukh and Hoskins 1988). That over Europe and Asia the precise mechanism for ENSO impacts remains less clear (Greatbatch et al 2004, Toniazzo and Scaife 2006, Bronnimann et al 2007)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
