scholarly journals Role of Low-Frequency Wind Variability in Inducing WWBs during the onset of super El Niños

2021 ◽  
Author(s):  
Yi-Kai Wu ◽  
Chi-Cherng Hong ◽  
Tim Li ◽  
An-Yi Huang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Low Frequency ◽  
Wind Fields ◽  
Wind Variability ◽  
The Pacific ◽  
Sst Anomaly ◽  
Wind Bursts

Abstract In this study, the effect of multiple timescale wind fields on the westerly wind bursts (WWBs) was investigated during the onset of super (1982, 1997, and 2015) and moderate El Niño events. The results revealed that extreme WWBs during the onset of the super El Niño group were attributed to low-frequency westerly (≥90 days, LFW), medium-frequency westerly (20–90 days, MFW, or intraseasonal) and high-frequency westerly (≤10 days, HFW) components, accounting for approximately 51%, 33% and 16%, respectively. Thus, the extreme WWBs during the onset of super El Niños were primarily contributed by LFWs and MFWs. By contrast, the WWBs during the onset of moderate El Niños were determined primarily by MFWs (38%) and HFWs (35%), whereas the LFW contribution is relatively small (27%). A further analysis indicated that LFWs during the onset of the super El Niños were primarily a response to a positive SST anomaly in the tropical to eastern North Pacific resembling the Pacific Meridional Mode (PMM), which had persisted during the preceding 9–12 months in the extratropical eastern North Pacific. A significant lagged correlation between the tropical and extratropical North Pacific SST was identified, and their correlation has become stronger since the late 1980s. MFWs during the onset of the super El Niños were primarily associated with the Madden-Julian Oscillation.

scholarly journals ENSO’s Modulation of Water Vapor Transport over the Pacific–North American Region

2015 ◽  
Vol 28 (9) ◽  
pp. 3846-3856 ◽  
Author(s):  
Hye-Mi Kim ◽  
Michael A. Alexander
Keyword(s):  
United States ◽  
El Niño ◽  
North Pacific ◽  
Moisture Transport ◽  
El Nino ◽  
Tropical Pacific ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Southwestern United States ◽  
The Pacific

Abstract The vertically integrated water vapor transport (IVT) over the Pacific–North American sector during three phases of ENSO in boreal winter (December–February) is investigated using IVT values calculated from the Climate Forecast System Reanalysis (CFSR) during 1979–2010. The shift of the location and sign of sea surface temperature (SST) anomalies in the tropical Pacific Ocean leads to different atmospheric responses and thereby changes the seasonal mean moisture transport into North America. During eastern Pacific El Niño (EPEN) events, large positive IVT anomalies extend northeastward from the subtropical Pacific into the northwestern United States following the anomalous cyclonic flow around a deeper Aleutian low, while a southward shift of the cyclonic circulation during central Pacific El Niño (CPEN) events induces the transport of moisture into the southwestern United States. In addition, moisture from the eastern tropical Pacific is transported from the deep tropical eastern Pacific into Mexico and the southwestern United States during CPEN. During La Niña (NINA), the seasonal mean IVT anomaly is opposite to that of two El Niño phases. Analyses of 6-hourly IVT anomalies indicate that there is strong moisture transport from the North Pacific into the northwestern and southwestern United States during EPEN and CPEN, respectively. The IVT is maximized on the southeastern side of a low located over the eastern North Pacific, where the low is weaker but located farther south and closer to shore during CPEN than during EPEN. Moisture enters the southwestern United States from the eastern tropical Pacific during NINA via anticyclonic circulation associated with a ridge over the southern United States.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

The essential role of early-spring westerly wind burst in generating the centennial extreme 1997/98 El Niño

2021 ◽  
pp. 1-38
Author(s):  
Tao Lian ◽  
Dake Chen
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Coupled Model ◽  
Early Spring ◽  
Strong Nonlinearity ◽  
Westerly Wind ◽  
Enso Dynamics

AbstractWhile both intrinsic low-frequency atmosphere–ocean interaction and multiplicative burst-like event affect the development of the El Niño–Southern Oscillation (ENSO), the strong nonlinearity in ENSO dynamics has prevented us from separating their relative contributions. Here we propose an online filtering scheme to estimate the role of the westerly wind bursts (WWBs), a type of aperiodic burst-like atmospheric perturbation over the western-central tropical Pacific, in the genesis of the centennial extreme 1997/98 El Niño using the CESM coupled model. This scheme highlights the deterministic part of ENSO dynamics during model integration, and clearly demonstrates that the strong and long-lasting WWB in March 1997 was essential for generating the 1997/98 El Niño. Without this WWB, the intrinsic low-frequency coupling would have only produced a weak warm event in late 1997 similar to the 2014/15 El Niño.

scholarly journals Influence of the 2015–2016 El Niño on the record-breaking mangrove dieback along northern Australia coast

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Abhik ◽  
Pandora Hope ◽  
Harry H. Hendon ◽  
Lindsay B. Hutley ◽  
Stephanie Johnson ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Multiple Linear Regression Model ◽  
Frequency Component ◽  
Enso Cycle ◽  
Northern Australia ◽  
Climate Conditions

AbstractThis study investigates the underlying climate processes behind the largest recorded mangrove dieback event along the Gulf of Carpentaria coast in northern Australia in late 2015. Using satellite-derived fractional canopy cover (FCC), variation of the mangrove canopies during recent decades are studied, including a severe dieback during 2015–2016. The relationship between mangrove FCC and climate conditions is examined with a focus on the possible role of the 2015–2016 El Niño in altering favorable conditions sustaining the mangroves. The mangrove FCC is shown to be coherent with the low-frequency component of sea level height (SLH) variation related to the El Niño Southern Oscillation (ENSO) cycle in the equatorial Pacific. The SLH drop associated with the 2015–2016 El Niño is identified to be the crucial factor leading to the dieback event. A stronger SLH drop occurred during austral autumn and winter, when the SLH anomalies were about 12% stronger than the previous very strong El Niño events. The persistent SLH drop occurred in the dry season of the year when SLH was seasonally at its lowest, so potentially exposed the mangroves to unprecedented hostile conditions. The influence of other key climate factors is also discussed, and a multiple linear regression model is developed to understand the combined role of the important climate variables on the mangrove FCC variation.

The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

2019 ◽  
Vol 32 (22) ◽  
pp. 7643-7661 ◽  
Author(s):  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Wenyu Zhou ◽  
Yu Zhang ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Deep Convection ◽  
Boreal Summer ◽  
Enso Events ◽  
The North ◽  
The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

scholarly journals PDO–ENSO Effects in the Climate of Mexico

2006 ◽  
Vol 19 (24) ◽  
pp. 6433-6438 ◽  
Author(s):  
Edgar G. Pavia ◽  
Federico Graef ◽  
Jorge Reyes
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Climate Anomalies ◽  
Enso Events ◽  
La Nina ◽  
Mean Temperature ◽  
The Pacific

Abstract The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.

scholarly journals The Role of Tropical Mean-State Biases in Modeled Winter Northern Hemisphere El Niño Teleconnections

2020 ◽  
Vol 33 (11) ◽  
pp. 4751-4768 ◽  
Author(s):  
Samantha Ferrett ◽  
Matthew Collins ◽  
Hong-Li Ren ◽  
Bo Wu ◽  
Tianjun Zhou
Keyword(s):  
Northern Hemisphere ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Teleconnection Pattern ◽  
The North ◽  
Precipitation Response ◽  
The North Pacific ◽  
Mean State

AbstractThe role of tropical mean-state biases in El Niño–Southern Oscillation teleconnections in the winter Northern Hemisphere is examined in coupled general circulation models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The main North Pacific teleconnection pattern, defined here by the strengths of the anomalous Kuroshio anticyclone and North Pacific cyclone, is linked to two anomalous Rossby wave sources that occur during El Niño: a negative source over East Asia and a positive source to the west of the North Pacific. Errors in the teleconnection pattern in models are associated with spatial biases in mean atmospheric ascent and descent and the strength of the corresponding forcing of Rossby waves via suppressed or enhanced El Niño precipitation responses in the tropical western North Pacific (WNP) and the equatorial central Pacific (CP). The WNP El Niño precipitation response is most strongly linked to the strength of the Kuroshio anticyclone and the CP El Niño precipitation response is most strongly linked to the strength of the North Pacific cyclone. The mean state and corresponding El Niño precipitation response can have seemingly distinct biases. A bias in the WNP does not necessarily correspond to a bias in the CP, suggesting that improvement of biases in both tropical WNP and equatorial CP regions should be considered for an accurate teleconnection pattern.

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