Impact of ENSO longitudinal position on teleconnections to the NAO

Abstract

While significant improvements have been made in understanding how the El Niño-Southern Oscillation (ENSO) impacts both North American and Asian climate, its relationship with the North Atlantic Oscillation (NAO) remains less clear. Observations indicate that ENSO exhibits a highly complex relationship with the NAO-associated atmospheric circulation. One critical contribution to this ambiguous ENSO/NAO relationship originates from ENSO's diversity in its spatial structure. In general, both eastern (EP) and central Pacific (CP) El Niño events tend to be accompanied by a negative NAO-like atmospheric response. However, for two different types of La Niña the NAO response is almost opposite. Thus, the NAO responses for the CP ENSO are mostly linear, while nonlinear NAO responses dominate for the EP ENSO. These contrasting extra-tropical atmospheric responses are mainly attributed to nonlinear air-sea interactions in the tropical eastern Pacific. The local atmospheric response to the CP ENSO sea surface temperature (SST) anomalies is highly linear since the air-sea action center is located within the Pacific warm pool, characterized by relatively high climatological SSTs. In contrast, the EP ENSO SST anomalies are located in an area of relatively low climatological SSTs in the eastern equatorial Pacific. Here only sufficiently high positive SST anomalies during EP El Niño events are able to overcome the SST threshold for deep convection, while hardly any anomalous convection is associated with EP La Niña SSTs that are below this threshold. This ENSO/NAO relationship has important implications for NAO seasonal prediction and places a higher requirement on models in reproducing 3 the full diversity of ENSO.

Asymmetric responses of the Philippine Sea anomalous anticyclone/cyclone to two types of El Niño–Southern Oscillation during the boreal winter

“…Previous works have also shown that EP ENSO generates teleconnections with much stronger asymmetric features than those under CP ENSO (Frauen et al ., ; Feng et al ., ; Zhang et al ., ). In comparison to CP ENSO, the strong asymmetric impacts caused by EP ENSO are inherently unavoidable, because the preference location that EP ENSO often occurs is over the eastern Pacific, where the zonal climatological SST is characterized by strong asymmetry.…”

Impacts of Different Types of ENSO Events on Thermocline Variability in the Southern Tropical Indian Ocean

“…Here the indices of Ren and Jin (2011) are used in correlation analysis because the EP and CP ENSO based on their indices can be better separated due to their low correlation. In addition, these previously mentioned indices could identify two types of El Niño but fail to distinguish different La Niña types (Zhang, Wang, Xiang, et al, 2015), including the indices of Ren and Jin (2011 1982, 1986, 1991, 1997, and 2015 (1994, 2002, 2004, and 2009), and the EP (CP) La Niña years are 1984, 1985, 1995, 1999, 2005, and 2007 (1983, 1988, 1998, 2000, 2008, 2010, and 2011). Please note that our qualitative conclusions remain the same if we use the other EP/CP index mentioned above.…”

“…During past decades, ENSO events have been divided into two different types: the central-Pacific (CP) and the eastern-Pacific (EP) El Niño/La Niña, with maximum positive/negative SST anomalies (SSTA) located in the central Pacific and the eastern equatorial Pacific, respectively (Ashok et al, 2007;Kao & Yu, 2009;Kug et al, 2009;Lee & McPhaden, 2010;Pan et al, 2018;Ren & Jin, 2011;Yu et al, 2011;Zhang, Wang, Xiang, et al, 2015, Zhang, Wang, Jin, et al, 2015. These two types of ENSO events are different in terms of their formation mechanisms and teleconnection signals (Ashok & Yamagata, 2009; and may induce different impacts on Z20 variability in the Indian Ocean, especially in the STIO region.…”

“…Furthermore, the method ofZhang et al (2019) is used in composite analysis because it can effectively distinguish two types for both El Niño and La Niña events. Furthermore, the method ofZhang et al (2019) is used in composite analysis because it can effectively distinguish two types for both El Niño and La Niña events.…”

“…). Furthermore, the method ofZhang et al (2019) is used in composite analysis because it can effectively distinguish two types for both El Niño and La Niña events. This criterion classifies different ENSO types based on the boreal winter (December-January-February; DJF) Niño3.4 index (5°S-5°N and 120-170°W).…”