Atmospheric Forcing of the Pacific Meridional Mode: Tropical Pacific‐Driven Versus Internal Variability

Zhang, Yu; Yu, Shiyun; Amaya, Dillon J.; Kosaka, Yu; Stuecker, Malte F.; Yang, Jun‐Chao; Lin, Xiaopei; Fan, Lei

doi:10.1029/2022gl098148

Cited by 12 publications

(9 citation statements)

References 28 publications

(50 reference statements)

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“…Here we identify that the PMM mechanism (emphasizing its crucial role) is more important than the OHC mechanism in generating multi-year LN events. The PMM mechanism not only influences tropical Pacific variability and triggers ENSO events but can also be triggered by ENSO events 9 , 10 , 44 , 45 , leading to another ENSO event with the same phase and resulting in a multi-year event 9 – 12 , 17 , 46 .…”

Section: Resultsmentioning

confidence: 99%

Overemphasized role of preceding strong El Niño in generating multi-year La Niña events

Kim,

Yu,

Tian

2023

Nat Commun

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Previous studies have emphasized the significance of a strong El Niño preceding La Niña (LN) in the formation of multi-year LN events due to the slow recharge-discharge ocean heat content process. However, observational analyses from 1900 to 2022 reveal that the majority (64%) of multi-year LN events did not necessitate a preceding strong El Niño to generate their second LN, suggesting an overemphasis on traditional views. Instead, here we show that a negative phase of the North Pacific Meridional Mode (PMM) during spring, when the first LN begins to decay, activates the mechanism responsible for triggering another LN and producing a multi-year event. The westward extension of the first LN’s cold anomalies, which interact directly with the eastern edge of the western Pacific warm pool, is highlighted as a crucial factor in the occurrence of a negative PMM. Additionally, the PMM mechanism can create a third LN, leading to triple-dip events.

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Section: Resultsmentioning

confidence: 99%

Overemphasized role of preceding strong El Niño in generating multi-year La Niña events

Kim,

Yu,

Tian

2023

Nat Commun

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“…For convenience, when the pattern has negative SLP anomalies to the south and positive to the north, it is defined as the positive NPO phase. Previous studies have suggested that the ENSO can influence the NPO [55][56][57][58] . To minimize the possible simultaneous ENSO impact on NPO, we linearly removed the ENSO signal 59,60 , which is represented by the Niño3.4 index, from both NPO and circulation fields, before conducting further analyses.…”

Section: Observational Analysis and Definitionsmentioning

confidence: 97%

Part I observational study on a new mechanism for North Pacific Oscillation influencing the tropics

et al. 2023

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The North Pacific Oscillation (NPO), a representative midlatitude atmospheric variability, plays an important role in the development of the El Niño-Southern Oscillation (ENSO). To explain this extratropical–tropical linkage, previous studies have focused on the atmospheric boundary layer processes coupled with the mixed-layer ocean. Different from the existing hypothesis, in this study, we propose a new mechanism to link the NPO to ENSO via upper-tropospheric teleconnections. Analyses of the wave activity flux show that wave energy associated with the NPO directly propagates from midlatitude to the tropics, modulating the tropical circulation. During the NPO event, this equatorward energy flux becomes pronounced after the NPO peak phase and persists for more than two weeks. As a result, when a positive NPO grows (here, north anticyclonic–south cyclonic circulation), upper-level easterly wind anomalies are situated along the equatorial Pacific. Accordingly, anomalous lower-level westerly winds simultaneously occur in the equatorial Pacific, contributing to the development of El Niño events. To demonstrate the wave energy propagation via the upper-level troposphere, a stationary wave model experiment was performed with an NPO-like barotropic vorticity forcing. The results show equatorward wave propagation consistent with the observation.

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“…In these studies, the PMM‐ENSO connection is a one‐way relationship (i.e., the PMM influences ENSO). Whereas recently, more and more investigations have pointed out that the preceding ENSO‐related SST anomaly in the central tropical Pacific (CTP) can in turn promote the occurrence and development of an in‐phase PMM event by exciting poleward atmospheric wave responses (Di Lorenzo et al., 2015; Fan et al., 2023; Fang & Yu, 2020; Stuecker, 2018; Yeh et al., 2018; Zhang et al., 2022). Now then, PMM events can accordingly be divided into two types: “stochastic” events forced by occasional extratropical atmospheric anomalies and “successive” events forced by ENSO‐related tropical SST anomaly.…”

Section: Introductionmentioning

confidence: 99%

Asymmetry Between Positive and Negative Phases of the Pacific Meridional Mode: A Contributor to ENSO Transition Complexity

Fan

Wang

Yang

2023

Geophysical Research Letters

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The Pacific Meridional Mode (PMM) is a leading mode of ocean-atmospheric coupled variability in the North Pacific, which is characterized by warm sea-surface temperature (SST) and overlaying southwesterly wind anomalies that extend from Baja California to the central equatorial Pacific in its positive phase (Chiang & Vimont, 2004). It is well documented that the PMM is an important modulator for El Niño-Southern Oscillation (ENSO) development and prediction (

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Atmospheric Forcing of the Pacific Meridional Mode: Tropical Pacific‐Driven Versus Internal Variability

Cited by 12 publications

References 28 publications

Overemphasized role of preceding strong El Niño in generating multi-year La Niña events

Overemphasized role of preceding strong El Niño in generating multi-year La Niña events

Part I observational study on a new mechanism for North Pacific Oscillation influencing the tropics

Asymmetry Between Positive and Negative Phases of the Pacific Meridional Mode: A Contributor to ENSO Transition Complexity

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