The Pacific Meridional Mode as a trigger for ENSO in a high-resolution coupled model

2013 ◽  
Vol 40 (12) ◽  
pp. 3189-3194 ◽  
Author(s):  
Sarah Larson ◽  
Ben Kirtman
Keyword(s):  
High Resolution ◽  
Coupled Model ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

scholarly journals Modeling the Mechanisms of Linear and Nonlinear ENSO Responses to the Pacific Meridional Mode

2016 ◽  
Vol 29 (24) ◽  
pp. 8745-8761 ◽  
Author(s):  
Erin E. Thomas ◽  
Daniel J. Vimont
Keyword(s):  
Southern Oscillation ◽  
Surface Wind ◽  
Coupled Model ◽  
Enso Event ◽  
Ocean Dynamics ◽  
Large Variability ◽  
Enso Events ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

Abstract Interactions between the Pacific meridional mode (PMM) and El Niño–Southern Oscillation (ENSO) are investigated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) and an intermediate coupled model (ICM). The two models are configured so that the CESM simulates the PMM but not ENSO, and the ICM simulates ENSO but not the PMM, allowing for a clean separation between the PMM evolution and the subsequent ENSO response. An ensemble of CESM simulations is run with an imposed surface heat flux associated with the North Pacific Oscillation (NPO) generating a sea surface temperature (SST) and wind response representative of the PMM. The PMM wind is then applied as a forcing to the ICM to simulate the ENSO response. The positive (negative) ensemble-mean PMM wind forcing results in a warm (cold) ENSO event although the responses are not symmetric (warm ENSO events are larger in amplitude than cold ENSO events), and large variability between ensemble members suggests that any individual ENSO event is strongly influenced by natural variability contained within the CESM simulations. Sensitivity experiments show that 1) direct forcing of Kelvin waves by PMM winds dominates the ENSO response, 2) seasonality of PMM forcing and ENSO growth rates influences the resulting ENSO amplitude, 3) ocean dynamics within the ICM dominate the ENSO asymmetry, and 4) the nonlinear relationship between PMM wind anomalies and surface wind stress may enhance the La Niña response to negative PMM variations. Implications for ENSO variability are discussed.

Influence of Pacific meridional mode on ENSO evolution and predictability: asymmetric modulation and ocean preconditioning

2020 ◽  
Author(s):  
Hanjie Fan ◽  
Bohua Huang ◽  
Song Yang
Keyword(s):  
Deep Convection ◽  
Low Frequency ◽  
Heat Content ◽  
Coupled Model ◽  
Enso Event ◽  
Ensemble Prediction ◽  
Enso Events ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

<p>This study investigates the mechanisms for the Pacific meridional mode (PMM) to influence the development of an ENSO event and its seasonal predictability. To examine the relative importance of several factors that might modulate the efficiency of the PMM influence, we conduct a series of prediction experiments to selected ENSO events with different intensity from a long simulation of the Community Earth System Model (CESM). Using the same coupled model, each of the ensemble prediction is conducted from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. In general, the matched PMM forcing to ENSO, i.e., a positive (negative) PMM prior to an El Niño (a La Niña), plays an enhancing role while a mismatched PMM forcing plays a damping role. For the matched PMM-ENSO events, the positive PMM exerts greater influence than its negative counterpart does, with stronger enhancement of positive PMM events on an El Niño than that of negative PMM events on a La Niña. This asymmetry in ENSO influence largely originates from the intensity asymmetry between the positive and negative PMM events in the tropics, which can be explained by the nonlinearity in the growth and equatorward propagation of the PMM-related SST and surface zonal wind anomalies through both wind-evaporation-SST (WES) feedback and summer deep convection (SDC) response. Furthermore, the response of ENSO to an imposed PMM forcing is modulated by the preconditioning of the upper ocean heat content, which provides the memory for the coupled low-frequency evolution in the tropical Pacific.</p>

Impacts of the Pacific Meridional Mode on June-August precipitation in the Amazon River Basin

2017 ◽  
Vol 143 (705) ◽  
pp. 1936-1945 ◽  
Author(s):  
Wei Zhang ◽  
Gabriele Villarini ◽  
Gabriel A. Vecchi
Keyword(s):  
River Basin ◽  
Amazon River ◽  
Amazon River Basin ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

scholarly journals Strong Modulation of the Pacific Meridional Mode on the Occurrence of Intense Tropical Cyclones over the Western North Pacific

2018 ◽  
Vol 31 (19) ◽  
pp. 7739-7749 ◽  
Author(s):  
Si Gao ◽  
Langfeng Zhu ◽  
Wei Zhang ◽  
Zhifan Chen
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Vertical Wind Shear ◽  
Low Level ◽  
The Pacific ◽  
Main Development ◽  
Development Region ◽  
Meridional Mode ◽  
Pacific Meridional Mode

This study finds a significant positive correlation between the Pacific meridional mode (PMM) index and the frequency of intense tropical cyclones (TCs) over the western North Pacific (WNP) during the peak TC season (June–November). The PMM influences the occurrence of intense TCs mainly by modulating large-scale dynamical conditions over the main development region. During the positive PMM phase, anomalous off-equatorial heating in the eastern Pacific induces anomalous low-level westerlies (and cyclonic flow) and upper-level easterlies (and anticyclonic flow) over a large portion of the main development region through a Matsuno–Gill-type Rossby wave response. The resulting weaker vertical wind shear and larger low-level relative vorticity favor the genesis of intense TCs over the southeastern part of the WNP and their subsequent intensification over the main development region. The PMM index would therefore be a valuable predictor for the frequency of intense TCs over the WNP.

Does the Pacific meridional mode dominantly affect tropical cyclogenesis in the western North Pacific?

2020 ◽  
Vol 55 (11-12) ◽  
pp. 3469-3483
Author(s):  
Hongjie Zhang ◽  
Liang Wu ◽  
Ronghui Huang ◽  
Jau-Ming Chen ◽  
Tao Feng
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Tropical Cyclogenesis ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

scholarly journals Linking the North American Dipole to the Pacific Meridional Mode

2019 ◽  
Vol 124 (6) ◽  
pp. 3020-3034 ◽  
Author(s):  
Ruiqiang Ding ◽  
Jianping Li ◽  
Yu‐heng Tseng ◽  
Cheng Sun ◽  
Yang Li ◽  
...  
Keyword(s):  
North American ◽  
The North ◽  
The Pacific ◽  
Meridional Mode ◽  
Pacific Meridional Mode

scholarly journals Summer High Temperature Extremes over China Linked to the Pacific Meridional Mode

2020 ◽  
Vol 33 (14) ◽  
pp. 5905-5917
Author(s):  
Ming Luo ◽  
Ngar-Cheung Lau ◽  
Wei Zhang ◽  
Qiang Zhang ◽  
Zhen Liu
Keyword(s):  
High Temperature ◽  
Land Surface ◽  
Southern China ◽  
Eastern China ◽  
Northern China ◽  
Temperature Extremes ◽  
The Pacific ◽  
Meridional Mode ◽  
High Temperature Extremes ◽  
Pacific Meridional Mode

AbstractThis study investigates the association between summer high temperature extremes (HTEs) over China and the Pacific meridional mode (PMM) that is characterized by an anomalous north–south sea surface temperature gradient and an anomalous surface circulation over the northeastern subtropical Pacific. It is found that the HTE activities over most parts of southern China (particularly eastern China) are prominently intensified during the positive PMM phase and weakened during the negative phase. Further examinations suggest that the PMM is linked with HTEs in China through processes that entail both eastward and westward development of signals emanating from the PMM site. The westward development is associated with the formation of an anomalous low-level cyclone over the western North Pacific (WNP), which may be viewed as a Matsuno–Gill-type response to the off-equatorial heating in the eastern Pacific. This circulation change is accompanied by anomalous ascent over WNP and northern China, and subsidence over eastern China. On the other hand, the eastward development process is linked to the PMM-induced displacement of the East Asian jet stream and the generation of a midlatitude Rossby wave train. In the positive PMM phase, the above circulation changes are accompanied by anomalous air subsidence and enhanced adiabatic heating, reduced precipitation, anomalous lower-level anticyclone, and rising surface pressure over the eastern part of China. Moreover, the land surface of that region receives more solar radiation. Opposite changes are discernible over northern China. These changes are favorable for the occurrence and persistence of HTEs over eastern China and tend to suppress HTEs over northern China.

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