An alterative effect by the tropical North Atlantic SST in intraseasonally varying El Niño teleconnection over the North Atlantic

Mi-Kyung Sung,Soon-Il An,Yoo-Geun Ham,Jong-Seong Kug

doi:10.3402/tellusa.v65i0.19863

Abstract

ABSTRACTIt is known that there is a distinct intraseasonal variation in wintertime atmospheric responses to El Niño over the North Atlantic, namely a positive North Atlantic Oscillation (NAO)-like response during early winter (November to December) and a negative NAO-like response during late winter (January to March). In this article, we suggest that the tropical North Atlantic (TNAL) sea surface temperatures (SSTs) significantly alter the North Atlantic atmospheric response to El Niño: the warm TNAL SST condition intensifies the negative NAO-like response and vice versa. During late El Niño winters, the TNAL SST tends to increase due to the atmospheric bridge between the tropical Pacific and the Atlantic oceans. The warm tendency in the TNAL SST can intensify the height contrast in the El Niño teleconnection between early and late winter. During early winter (when the response of the TNAL SST to El Niño has not been established yet), atmospheric circulation over the North Atlantic varies widely under various TNAL conditions. Consequently, the average influence of El Niño over the North Atlantic region becomes weaker in the early winter. By contrast, the overall warming over the TNAL region during the late El Niño winter is conducive to the formation of a negative NAO pattern. As a result, the climatic impact becomes stronger during the late winter.

Highlights

El Nino has been of interest to researchers due to its considerable impact on the global climate
Pozo-Vazquez et al (2001) reported that no statistically significant sea level pressure (SLP) anomaly patterns were found to be associated with El Nino, while a statistically significant pattern resembling the positive phase of the North Atlantic Oscillation (NAO) was found during La Nina events
Studies have shown that the remote effect of El Nino differs markedly between early and late winter over the North American and North Atlantic regions (Montroy, 1997; Montroy et al, 1998; Wang and Fu, 2000; Moron and Gouirand, 2003)

Summary

Introduction

El Nino has been of interest to researchers due to its considerable impact on the global climate. By contrast, Mathieu et al (2004) argued that the El Nino-Southern Oscillation (ENSO) event has significantly influenced the climates of the North Atlantic and European regions, but the impact of the ENSO varies between individual events They suggested that differences in individual ENSO events arise partly from differences in Indo-Pacific sea surface temperatures (SSTs), and partly from differences in Atlantic SSTs. Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The stratospheric response to El Nino has been identified to be attributed to the seasonal dependency of the remote impact over the North Atlantic region (Sassi et al, 2004; Bell et al, 2009; Cagnazzo and Manzini, 2009; Ineson and Scaife, 2009) According to these studies, a weakened stratospheric polar vortex can initiate a negative NAO pattern in the troposphere during late winter.

Data and methodologies

Results

Discussion

Summary and conclusion