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>

scholarly journals Influence of Pacific Meridional Mode on ENSO evolution and predictability: Asymmetric modulation and ocean preconditioning

2020 ◽  
pp. 1-61
Author(s):  
Hanjie Fan ◽  
Bohua Huang ◽  
Song Yang ◽  
Wenjie Dong
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Enso Event ◽  
La Niña ◽  
Enso Events ◽  
La Nina ◽  
Meridional Mode ◽  
Pacific Meridional Mode

AbstractThis study investigates the mechanisms behind the Pacific Meridional Mode (PMM) in influencing the development of El Niño-Southern Oscillation (ENSO) event and its seasonal predictability. To examine the relative importance of various factors that may modulate the efficiency of the PMM influence, a series of experiments are conducted for selected ENSO events with different intensity using the Community Earth System Model, in which ensemble predictions are made from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. Overall, 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 cases, a positive PMM event enhances an El Niño more strongly than a negative PMM event enhances a La Niña. This asymmetry in influencing ENSO largely originates from the asymmetry in intensity 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 anomalies of sea surface temperature (SST) and surface zonal wind through both wind-evaporation-SST feedback and summer deep convection response. Our model results also indicate that the PMM acts as a modulator rather than a trigger for the occurrence of ENSO event. 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.

scholarly journals Linking the Pacific Meridional Mode to ENSO: Coupled Model Analysis

2009 ◽  
Vol 22 (12) ◽  
pp. 3488-3505 ◽  
Author(s):  
Li Zhang ◽  
Ping Chang ◽  
Link Ji
Keyword(s):  
Southern Oscillation ◽  
Coupled Model ◽  
Enso Event ◽  
Boreal Spring ◽  
Enso Events ◽  
Maximum Variance ◽  
Surface Circulation ◽  
The Pacific ◽  
Anomalous Surface ◽  
Thermodynamic Coupling

Abstract The occurrence of a boreal spring phenomenon referred to as the Pacific meridional model (MM) is shown to be intimately linked to the development of El Niño–Southern Oscillation (ENSO) in a long simulation of a coupled model. The MM, characterized by an anomalous north–south SST gradient and anomalous surface circulation in the northeasterly trade regime with maximum variance in boreal spring, is shown to be inherent to thermodynamic ocean–atmosphere coupling in the intertropical convergence zone (ITCZ) latitude, and the MM existence is independent of ENSO. The thermodynamic coupling enhances the persistence of the anomalous winds in the deep tropics, forcing energetic equatorially trapped oceanic waves to occur in the central western Pacific, which in turn initiate an ENSO event. The majority of ENSO events in both nature and the coupled model are preceded by MM events.

Simulating ENSO SSTAs from TAO/TRITON Winds: The Impacts of 20 Years of Buoy Observations in the Pacific Waveguide and Comparison with Reanalysis Products

2017 ◽  
Vol 30 (3) ◽  
pp. 1041-1059 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
Southern Oscillation ◽  
Surface Wind ◽  
Major Elements ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Wind Fields ◽  
Enso Events ◽  
The Pacific ◽  
The Impact

Abstract The fundamental importance of near-equatorial zonal wind stress in the evolution of the tropical Pacific Ocean’s seasonal cycle and El Niño–Southern Oscillation (ENSO) events is well known. It has been two decades since the TAO/TRITON buoy array was deployed, in part to provide accurate surface wind observations across the Pacific waveguide. It is timely to revisit the impact of TAO/TRITON winds on our ability to simulate and thereby understand the evolution of sea surface temperature (SST) in this region. This work shows that forced ocean model simulations of SST anomalies (SSTAs) during the periods with a reasonably high buoy data return rate can reproduce the major elements of SSTA variability during ENSO events using a wind stress field computed from TAO/TRITON observations only. This demonstrates that the buoy array usefully fulfills its waveguide-wind-measurement purpose. Comparison of several reanalysis wind fields commonly used in recent ENSO studies with the TAO/TRITON observations reveals substantial biases in the reanalyses that cause substantial errors in the variability and trends of the reanalysis-forced SST simulations. In particular, the negative trend in ERA-Interim is much larger and the NCEP–NCAR Reanalysis-1 and NCEP–DOE Reanalysis-2 variability much less than seen in the TAO/TRITON wind observations. There are also mean biases. Thus, even with the TAO/TRITON observations available for assimilation into these wind products, there remain oceanically important differences. The reanalyses would be much more useful for ENSO and tropical Pacific climate change study if they would more effectively assimilate the TAO/TRITON observations.

scholarly journals Linking the Pacific Meridional Mode to ENSO: Utilization of a Noise Filter

2009 ◽  
Vol 22 (4) ◽  
pp. 905-922 ◽  
Author(s):  
Li Zhang ◽  
Ping Chang ◽  
Michael K. Tippett
Keyword(s):  
Heat Flux ◽  
Wind Stress ◽  
Surface Wind ◽  
Atmospheric Variability ◽  
Surface Wind Stress ◽  
Noise Filter ◽  
The Pacific ◽  
Meridional Mode ◽  
The Impact ◽  
Pacific Meridional Mode

Abstract A novel noise filter is used to effectively reduce internal atmospheric variability in the air–sea fluxes of a coupled model. This procedure allows for a test of the impact of the internal atmospheric variability on ENSO through its effect on the Pacific meridional mode (MM). Three 100-yr coupled experiments are conducted, where the filter is utilized to suppress internal atmospheric variability in 1) both the surface wind stress and the heat flux (fully filtered run), 2) only the surface heat flux (filtered-flux run), and 3) only the surface wind stress (filtered-wind run). The fully filtered run indicates that suppressing internal atmospheric variability weakens the MM, which in turn results in substantially reduced ENSO variability. ENSO is no longer phase locked to the boreal winter. The filtered-flux and filtered-wind experiments reveal that different types of noise affect ENSO in different ways. The noise in the wind stress does not have a significant impact on the MM and its relationship to ENSO. This type of noise, however, tends to broaden the spectral peak of ENSO while shifting it toward lower frequencies. The noise in the heat flux, on the other hand, has a direct impact on the strength of the MM and consequently its ability to influence ENSO. Reducing the effect of heat flux noise yields substantially weakened MM activity and a weakened relationship to ENSO, which leads to altered seasonal phase-locking characteristics.

scholarly journals The Linear Response of ENSO to the Madden–Julian Oscillation

2005 ◽  
Vol 18 (13) ◽  
pp. 2441-2459 ◽  
Author(s):  
J. Zavala-Garay ◽  
C. Zhang ◽  
A. M. Moore ◽  
R. Kleeman
Keyword(s):  
Large Fraction ◽  
Surface Wind ◽  
Low Frequency ◽  
Coupled Model ◽  
Cumulative Effect ◽  
Enso Event ◽  
Kelvin Waves ◽  
Madden Julian Oscillation ◽  
Coupled Models ◽  
Stochastic Forcing

Abstract The possibility that the tropical Pacific coupled system linearly amplifies perturbations produced by the Madden–Julian oscillation (MJO) is explored. This requires an estimate of the low-frequency tail of the MJO. Using 23 yr of NCEP–NCAR reanalyses of surface wind and Reynolds SST, we show that the spatial structure that dominates the intraseasonal band (i.e., the MJO) also dominates the low-frequency band once the anomalies directly related to ENSO have been removed. This low-frequency contribution of the intraseasonal variability is not included in most ENSO coupled models used to date. Its effect in a coupled model of intermediate complexity has, therefore, been studied. It is found that this “MJO forcing” (τMJO) can explain a large fraction of the interannual variability in an asymptotically stable version of the model. This interaction is achieved via linear dynamics. That is, it is the cumulative effect of individual events that maintains ENSOs in this model. The largest coupled wind anomalies are initiated after a sequence of several downwelling Kelvin waves of the same sign have been forced by τMJO. The cumulative effect of the forced Kelvin waves is to persist the (small) SST anomalies in the eastern Pacific just enough for the coupled ocean–atmosphere dynamics to amplify the anomalies into a mature ENSO event. Even though τMJO explains just a small fraction of the energy contained in the stress not associated with ENSO, a large fraction of the modeled ENSO variability is excited by this forcing. The characteristics that make τMJO an optimal stochastic forcing for the model are discussed. The large zonal extent is an important factor that differentiates the MJO from other sources of stochastic forcing.

scholarly journals LINEARIZATION OF RELATIVE HUMIDITY OVER THE PACIFIC OCEAN ON THE EQUATORIAL LINE

2019 ◽  
Vol 16 (33) ◽  
pp. 630-640
Author(s):  
C. M. DÍEZ ◽  
C. J. SOLANO
Keyword(s):  
Pacific Ocean ◽  
Relative Humidity ◽  
Earth Science ◽  
Southern Oscillation ◽  
Correlation Coefficients ◽  
East Side ◽  
The West ◽  
Enso Events ◽  
The Pacific ◽  
The Pacific Ocean

The atmosphere system is ruled by the interaction of many meteorological parameters, causing a dependency between them, i.e., moisture and temperature, both suitable in front of any anomaly, such as storms, hurricanes, El Niño-Southern Oscillation (ENSO) events. So, understanding perturbations of the variation of moistness along the time may provide an indicator of any oceanographic phenomenon. Annual relative humidity data around the Equatorial line of the Pacific Ocean were processed and analyzed to comprehend the time evolution of each dataset, appreciate anomalies, trends, histograms, and propose a way to predict anomalous episodes such ENSO events, observing abnormality of lag correlation coefficients between every pair of buoys. Datasets were taken from the Tropical Atmosphere Ocean / Triangle Trans-Ocean Network (TAO/TRITON) project, array directed by Pacific Environmental Laboratory (PMEL) of the National Oceanic and Atmospheric Administration (NOAA), and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). All the datasets were processed, and the code was elaborated by the author or adapted from Mathworks Inc. Even occurrences of relative humidity in the east side of the Pacific Ocean seem to oscillate harmonically, while occurrences in the west side, do not, because of the size of their amplitudes of oscillations. This fact can be seen in the histograms that show Peak shapes in the east side of the ocean, and Gaussians in the west; lag correlation functions show that no one pair of buoys synchronize fluctuations, but western buoys are affected in front of ENSO events, especially between 1997-98. Definitely, lag correlations in western buoys are determined to detect ENSO events.

On the influence of ENSO complexity on Pan-Pacific coastal wave extremes

2021 ◽  
Vol 118 (47) ◽  
pp. e2115599118
Author(s):  
Julien Boucharel ◽  
Rafael Almar ◽  
Elodie Kestenare ◽  
Fei-Fei Jin
Keyword(s):  
Southern Oscillation ◽  
Wave Activity ◽  
Spatial Behavior ◽  
Coastal Hazards ◽  
Climate Control ◽  
Enso Events ◽  
The Pacific ◽  
Coastal Impacts ◽  
Climate Mode

Wind-generated waves are dominant drivers of coastal dynamics and vulnerability, which have considerable impacts on littoral ecosystems and socioeconomic activities. It is therefore paramount to improve coastal hazards predictions through the better understanding of connections between wave activity and climate variability. In the Pacific, the dominant climate mode is El Niño Southern Oscillation (ENSO), which has known a renaissance of scientific interest leading to great theoretical advances in the past decade. Yet studies on ENSO’s coastal impacts still rely on the oversimplified picture of the canonical dipole across the Pacific. Here, we consider the full ENSO variety to delineate its essential teleconnection pathways to tropical and extratropical storminess. These robust seasonally modulated relationships allow us to develop a mathematical model of coastal wave modulation essentially driven by ENSO’s complex temporal and spatial behavior. Accounting for this nonlinear climate control on Pan-Pacific wave activity leads to a much better characterization of waves’ seasonal to interannual variability (+25% in explained variance) and intensity of extremes (+60% for strong ENSO events), therefore paving the way for significantly more accurate forecasts than formerly possible with the previous baseline understanding of ENSO’s influence on coastal hazards.

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