A Nonstationary ENSO–NAO Relationship Due to AMO Modulation

Abstract

Many previous studies have demonstrated a high uncertainty in the relationship between El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). In the present work, decadal modulation by the Atlantic multidecadal oscillation (AMO) is investigated as a possible cause of the nonstationary ENSO–NAO relationship based on observed and reanalysis data. It is found that the negative ENSO–NAO correlation in late winter is significant only when ENSO and the AMO are in phase (AMO+/El Niño and AMO−/La Niña). However, no significant ENSO-driven atmospheric anomalies can be observed over the North Atlantic when ENSO and the AMO are out of phase (AMO−/El Niño and AMO+/La Niña). Further analysis indicates that the sea surface temperature anomaly (SSTA) in the tropical North Atlantic (TNA) plays an essential role in this modulating effect. Because of broadly analogous TNA SSTA responses to both ENSO and the AMO during late winter, a warm SSTA in the TNA is evident when El Niño occurs during a positive AMO phase, resulting in a significantly weakened NAO, and vice versa when La Niña occurs during a negative AMO phase. In contrast, neither the TNA SSTA nor the NAO shows a prominent change under out-of-phase combinations of ENSO and AMO. The AMO modulation and the associated effect of the TNA SSTA are shown to be well reproduced by historical simulations of the HadCM3 coupled model and further verified by forced experiments using an atmospheric circulation model. These offer hope that similar models will be able to make predictions for the NAO when appropriately initialized.

Simulated coordinated impacts of the previous autumn North Atlantic Oscillation (NAO) and winter El Niño on winter aerosol concentrations over eastern China

“…For example, it is reported that variation in boreal spring NAO influenced the subsequent intensity of the EASM from 1979 to 2006 (Wu et al, 2009). The linkage between the EASM and NAO has been further explored but on the interdecadal scale (Wu and Lin, 2012;Zuo et al, 2013), and it is suggested that the preceding spring NAO dominated the relationship of the NAO-EASM more than the simultaneous summer NAO; a similar result is seen in Zheng et al (2016). Xu et al (2013) presented the previous boreal summer NAO as significantly influencing the following September rainfall over central China.…”

Periodicity in Extreme Weather in the ‘Maritime Region’ of Eastern North America

“…Interactions between the cycles described above and their resultant in uence on climate are welldocumented. For example, AMO is known to weaken the effects of ENSO, NAO, and AO during its positive phase and amplify them during its negative phase (Zhang et al 2012;Kang et al 2014;Park and Li 2019;Zhang et al 2019;Chen et al 2020). Other climate oscillations thought to in uence weather only weakly in uence climate in the region, or occur with frequencies of hundreds or thousands of years, well beyond the instrumental records examined in this study (Mann et al 1995;Domínguez-Villar et al 2017).…”

“…AMO positive phases have been associated with several changes in climate, such as decreased precipitation, increased temperature, and droughts in North America (En eld et al 2001;Hodson 2005, 2007;Nigam et al 2011). However, in reference to extreme temperatures and precipitation, the AMO has a more prevalent impact on North America by modulating the effects of other climate phenomena (Mo et al 2009;Zhang et al 2012;Kang et al 2014;Park and Li 2019;Zhang et al 2019).…”

Nonlinearity in the Tropospheric Pathway of ENSO to the North Atlantic

“…Another important factor that can impact the ENSO teleconnection to the North Atlantic is decadal variability such as the Pacific Decadal Oscillation (PDO) (Rao et al, 2019) and the Atlantic Mutidecadal Oscillation (AMO) (Zhang et al, 2018).…”