Relationships between Extratropical Sea Level Pressure Variations and the Central Pacific and Eastern Pacific Types of ENSO

Abstract

This study examines the linkages between leading patterns of interannual sea level pressure (SLP) variability over the extratropical and the eastern Pacific (EP) and central Pacific (CP) types of El Niñ o-Southern Oscillation (ENSO). The first empirical orthogonal function (EOF) mode of the extratropical SLP anomalies represents variations of the Aleutian low, and the second EOF mode represents the North Pacific Oscillation (NPO) and is characterized by a meridional SLP anomaly dipole with a nodal point near 508N. It is shown that a fraction of the first SLP mode can be excited by both the EP and CP types of ENSO. The SLP response to the EP type is stronger and more immediate. The tropical-extratropical teleconnection appears to act more slowly for the CP ENSO. During the decay phase of EP events, the associated extratropical SLP anomalies shift from the first SLP mode to the second SLP mode. As the second SLP mode grows, subtropical SST anomalies are induced beneath via surface heat flux anomalies. The SST anomalies persist after the peak in strength of the second SLP mode, likely because of the seasonal footprinting mechanism, and lead to the development of the CP type of ENSO. This study shows that the CP ENSO is an extratropically excited mode of tropical Pacific variability and also suggests that the decay of an EP type of ENSO can lead to the onset of a CP type of ENSO with the aid of the NPO. This extratropical linking mechanism appears to be at work during the 1972, 1982, and 1997 strong El Niñ o events, which were all EP events and were all followed by strong CP La Niñ a events after the NPO was excited in the extratropics. This study concludes that extratropical SLP variations play an important role in exciting the CP type of ENSO and in linking the transitions from the EP to CP events.

Recent climate variation in the Bering and Chukchi Seas and its linkages to large-scale circulation in the Pacific

“…Di Lorenzo et al (2010) suggested that the CP El Niño is tightly linked to the NPGO pattern via atmospheric teleconnection of the NPO. More recent studies have noted that the mid-latitude NPO forcing is particularly influential in the initial establishment of SSTA in the tropical central Pacific for CP El Niño events (Furtado et al 2011;Kim et al 2012;Yu and Kim 2011). This covariability of the NPO, NPGO and CP El Niño is clearly demonstrated in the regression patterns over the Pacific basin in connection with the warming of the Bering and Chukchi Seas during 1999-2010 (Figs.…”

“…Furthermore, several recent studies argued that the initial establishment of SST anomalies in the tropical central Pacific is intimately tied to mid-latitude atmospheric variability, that is, the NPO pattern (Furtado et al 2011;Kim et al 2012;Yu and Kim 2011). The important links between the CP El Niño, the NPO and the NPGO constitute a prominent lowfrequency variability in the Pacific basin in the recent decade.…”

Asymmetry of the winter extra-tropical teleconnections in the Northern Hemisphere associated with two types of ENSO

“…It is completely different from the conventional ENSO with warming (cooling) SST anomalies in the tropical eastern Pacific (i.e., eastern-Pacific (EP) ENSO) in both the spatial pattern and climate impacts (Feng et al 2010(Feng et al , 2011Weng et al 2007;Wang and Wang 2014;Yang and Jiang 2014;Yu and Kim 2011;Zhang et al 2013; among others). For example, Weng et al (2007Weng et al ( , 2009 gave us a general comparison of the impacts of CP and EP El Niño on the Pacific rim regions for the winter and summer seasons.…”

“…For the CP-ENSO conditions, the atmospheric teleconnections exhibit a distinctive feature compared with those for the EP ENSO due to the different location of warming (cooling) SST anomalies (e.g., Li and Zhou 2012;Yu and Kim 2011;Weng et al 2009;Zhang et al 2014a, b). Do the impacts of CP El Niño and CP La Niña on the circulation anomalies have strong asymmetric signals just as the aforementioned conditions for the EP ENSO?…”

The salience of nonlinearities in the boreal winter response to ENSO: North Pacific and North America

“…Specifically, several papers have argued that the atmospheric response to EN events that peak in the central equatorial Pacific (CP EN events), also called dateline or Modoki EN events (Larkin and Harrison 2005;Ashok et al 2007), differs from that in response to EN events that peak in the eastern equatorial Pacific (EP EN events; see the recent review by Capotondi et al 2015). While all EN types lead to a deepened Aleutian low (Weng et al 2009;Yu and Kim 2011), it has been suggested that central Pacific (CP) EN leads to a westward and southward displacement of the deepened Aleutian low and different impacts on United States precipitation and temperature (Larkin and Harrison 2005;Weng et al 2009). …”