scholarly journals An Interhemispheric Tropical Sea Level Seesaw due to El Niño Taimasa

2014 ◽  
Vol 27 (3) ◽  
pp. 1070-1081 ◽  
Author(s):  
Matthew J. Widlansky ◽  
Axel Timmermann ◽  
Shayne McGregor ◽  
Malte F. Stuecker ◽  
Wenju Cai
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Pacific Islands ◽  
El Nino ◽  
Ocean Model ◽  
Trade Winds ◽  
Sea Levels ◽  
Sea Level Anomalies ◽  
El Niño Events ◽  
El Nino Events

Abstract During strong El Niño events, sea level drops around some tropical western Pacific islands by up to 20–30 cm. Such events (referred to as taimasa in Samoa) expose shallow reefs, thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls. During the termination of strong El Niño events, a southward movement of weak trade winds and the development of an anomalous anticyclone in the Philippine Sea are shown to force an interhemispheric sea level seesaw in the tropical Pacific that enhances and prolongs extreme low sea levels in the southwestern Pacific. Spectral features, in addition to wind-forced linear shallow water ocean model experiments, identify a nonlinear interaction between El Niño and the annual cycle as the main cause of these sea level anomalies.

scholarly journals Higher Sea Levels at Hawaii Caused by Strong El Niño and Weak Trade Winds

2020 ◽  
Vol 33 (8) ◽  
pp. 3037-3059 ◽  
Author(s):  
Xiaoyu Long ◽  
Matthew J. Widlansky ◽  
Fabian Schloesser ◽  
Philip R. Thompson ◽  
H. Annamalai ◽  
...  
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Ocean Model ◽  
Surface Cooling ◽  
Trade Winds ◽  
Sea Levels ◽  
El Niño Events ◽  
El Nino Events

AbstractHawaii experienced record-high sea levels during 2017, which followed the 2015 strong El Niño and coincided with weak trade winds in the tropical northeastern Pacific. The record sea levels were associated with a combination of processes, an important contributing factor of which was the persistent high sea level (~10 cm above normal) over a large region stretching between Hawaii and Mexico. High sea levels at Mexico are known to occur during strong El Niño as the coastal thermocline deepens. Planetary wave theory predicts that these coastal anomalies propagate westward into the basin interior; however, high sea levels at Hawaii do not occur consistently following strong El Niño events. In particular, Hawaii sea levels remained near normal following the previous strong El Niño of 1997. The processes controlling whether Hawaii sea levels rise after El Niño have so far remained unknown. Atmosphere-forced ocean model experiments show that anomalous surface cooling, controlled by variable trade winds, impacts sea level via mixed layer density, explaining much of the difference in Hawaiian sea level response after the two recent strong El Niño events. In climate model projections with greenhouse warming, more frequent weak trade winds following El Niño events are expected, suggesting that the occurrence of high sea levels at Hawaii will increase as oceanic anomalies more often traverse the basin.

scholarly journals On the role of the south Pacific subtropical high at the onset of El Niño events

2018 ◽  
Author(s):  
Youjia Zou ◽  
Xiangying Xi
Keyword(s):  
El Niño ◽  
El Nino ◽  
South Pacific ◽  
Warm Pool ◽  
Equatorial Pacific ◽  
Subtropical High ◽  
Trade Winds ◽  
Southward Shift ◽  
El Niño Events ◽  
El Nino Events

Abstract. Previous studies have suggested that an eastward propagation of the warm pool in the western Pacific during El Niño events may be induced by a weakening of the easterly Trade Winds (Alexander et al., 2002; Bjerknes, 1969). However, the dynamic mechanism of the Trade Winds weakening is not well understood. Here we use a model and other published proxy records to demonstrate that the anomalous southward shift of the south Pacific subtropical high (SPSH) may play a crucial role at the onset of El Niño events. By analyzing the relationship between the Trade Winds, the Equatorial Currents, the Eastern Boundary Currents and the SPSH, we find that an anomalous southward shift of the SPSH can result in a weakening of the SE Trade Winds and a southward intrusion of the NE Trade Winds, leading to a southward migration of the Trade Wind-induced Equatorial Currents, including the Equatorial Countercurrent (from ~5°–8° N to ~0°). The warm pool in the western equatorial Pacific is therefore forced to propagate eastward by the enhanced Equatorial Countercurrent and, thus, a warm phase in the central or the eastern equatorial Pacific. Moreover, the equatorward upwelling in the eastern South Pacific, usually recurving along the equator, shifts southward along with the SPSH, in turn diverts towards the west at ~15° S to feed the westward South Equatorial Currents, resulting in a failure of cooling sea surface in the eastern tropical Pacific, thus a flattening of the thermocline. The model experiments indicate that the meridional position and intensity of the Equatorial Countercurrent in the Pacific are some of the determining factors in giving rise to El Niño diversity, suggesting that there should be more frequent warm events due to a meridional expansion of the warm pool under global warming.

scholarly journals Influence of Arctic sea-ice variability on Pacific trade winds

2020 ◽  
Vol 117 (6) ◽  
pp. 2824-2834 ◽  
Author(s):  
Charles F. Kennel ◽  
Elena Yulaeva
Keyword(s):  
Sea Ice ◽  
El Niño ◽  
El Nino ◽  
Arctic Sea Ice ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Trade Winds ◽  
Upper Troposphere ◽  
El Niño Events ◽  
El Nino Events

A conceptual model connecting seasonal loss of Arctic sea ice to midlatitude extreme weather events is applied to the 21st-century intensification of Central Pacific trade winds, emergence of Central Pacific El Nino events, and weakening of the North Pacific Aleutian Low Circulation. According to the model, Arctic Ocean warming following the summer sea-ice melt drives vertical convection that perturbs the upper troposphere. Static stability calculations show that upward convection occurs in annual 40- to 45-d episodes over the seasonally ice-free areas of the Beaufort-to-Kara Sea arc. The episodes generate planetary waves and higher-frequency wave trains that transport momentum and heat southward in the upper troposphere. Regression of upper tropospheric circulation data on September sea-ice area indicates that convection episodes produce wave-mediated teleconnections between the maximum ice-loss region north of the Siberian Arctic coast and the Intertropical Convergence Zone (ITCZ). These teleconnections generate oppositely directed trade-wind anomalies in the Central and Eastern Pacific during boreal winter. The interaction of upper troposphere waves with the ITCZ air–sea column may also trigger Central Pacific El Nino events. Finally, waves reflected northward from the ITCZ air column and/or generated by triggered El Nino events may be responsible for the late winter weakening of the Aleutian Low Circulation in recent years.

scholarly journals Variability of the Mindanao Current Induced by El Niño Events

2020 ◽  
Vol 50 (6) ◽  
pp. 1753-1772 ◽  
Author(s):  
Qiuping Ren ◽  
Yuanlong Li ◽  
Fan Wang ◽  
Jing Duan ◽  
Shijian Hu ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Wind Forcing ◽  
Ekman Pumping ◽  
El Niño Events ◽  
Mindanao Current ◽  
El Nino Events

AbstractHistorical observations have documented prominent changes of the Mindanao Current (MC) during El Niño events, yet a systematic understanding of how El Niño modulates the MC is still lacking. Mooring observations during December 2010–August 2014 revealed evident year-to-year variations of the MC in the upper 400 m that were well reproduced by the Hybrid Coordinate Ocean Model (HYCOM). Composite analysis was conducted for 10 El Niño events during 1980–2015 using five model-based datasets (HYCOM, OFES, GEOS-ODA, SODA2.2.4, and SODA3.3.1). A consensus is reached in suggesting that a developing (decaying) El Niño strengthens (weakens) the MC, albeit with quantitative differences among events and datasets. HYCOM experiments demonstrate that the MC variability is mainly a first baroclinic mode response to surface wind forcing of the tropical Pacific, but the specific mechanism varies with latitude. The upstream part of the MC north of 7.5°N is controlled by wind forcing between 6° and 9°N through Ekman pumping, whereas its downstream part south of 7.5°N is greatly affected by equatorial winds. Prevailing westerly winds and Ekman upwelling in the developing stage cause cyclonic anomalous circulation in the northwest tropical Pacific that strengthens the MC, and the opposite surface wind forcing effect in the decaying stage weakens the MC. Although ocean models show difficulties in realistically representing the northward-flowing Mindanao Undercurrent (MUC) beneath the MC and its seasonal and interannual variations, all five products suggest an enhancement of the MUC during the decaying stage of El Niño.

scholarly journals Optimally growing initial errors of El Niño events in the CESM

2021 ◽  
Author(s):  
Hui Xu ◽  
Lei Chen ◽  
Wansuo Duan
Keyword(s):  
El Niño ◽  
El Nino ◽  
Equatorial Pacific ◽  
Initial Error ◽  
Initial Errors ◽  
El Niño Events ◽  
Type 3 ◽  
El Nino Events

AbstractThe optimally growing initial errors (OGEs) of El Niño events are found in the Community Earth System Model (CESM) by the conditional nonlinear optimal perturbation (CNOP) method. Based on the characteristics of low-dimensional attractors for ENSO (El Niño Southern Oscillation) systems, we apply singular vector decomposition (SVD) to reduce the dimensions of optimization problems and calculate the CNOP in a truncated phase space by the differential evolution (DE) algorithm. In the CESM, we obtain three types of OGEs of El Niño events with different intensities and diversities and call them type-1, type-2 and type-3 initial errors. Among them, the type-1 initial error is characterized by negative SSTA errors in the equatorial Pacific accompanied by a negative west–east slope of subsurface temperature from the subsurface to the surface in the equatorial central-eastern Pacific. The type-2 initial error is similar to the type-1 initial error but with the opposite sign. The type-3 initial error behaves as a basin-wide dipolar pattern of tropical sea temperature errors from the sea surface to the subsurface, with positive errors in the upper layers of the equatorial eastern Pacific and negative errors in the lower layers of the equatorial western Pacific. For the type-1 (type-2) initial error, the negative (positive) temperature errors in the eastern equatorial Pacific develop locally into a mature La Niña (El Niño)-like mode. For the type-3 initial error, the negative errors in the lower layers of the western equatorial Pacific propagate eastward with Kelvin waves and are intensified in the eastern equatorial Pacific. Although the type-1 and type-3 initial errors have different spatial patterns and dynamic growing mechanisms, both cause El Niño events to be underpredicted as neutral states or La Niña events. However, the type-2 initial error makes a moderate El Niño event to be predicted as an extremely strong event.

scholarly journals Studies of the seasonal prediction of heavy late spring rainfall over southeastern China

2021 ◽  
Author(s):  
Shouwen Zhang ◽  
Hui Wang ◽  
Hua Jiang ◽  
Wentao Ma
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Lead Time ◽  
Heavy Rainfall ◽  
El Nino ◽  
Late Spring ◽  
Southeastern China ◽  
River Region ◽  
El Niño Events ◽  
El Nino Events

AbstractThe late spring rainfall may account for 15% of the annual total rainfall, which is crucial to early planting in southeastern China. A better understanding of the precipitation variations in the late spring and its predictability not only greatly increase our knowledge of related mechanisms, but it also benefits society and the economy. Four models participating in the North American Multi-Model Ensemble (NMME) were selected to study their abilities to forecast the late spring rainfall over southeastern China and the major sources of heavy rainfall from the perspective of the sea surface temperature (SST) field. We found that the models have better abilities to forecast the heavy rainfall over the middle and lower reaches of the Yangtze River region (MLYZR) with only a 1-month lead time, but they failed for a 3-month lead time since the occurrence of the heavy rainfall was inconsistent with the observations. The observations indicate that the warm SST anomalies in the tropical eastern Indian Ocean are vital to the simultaneously heavy rainfall in the MLYZR in May, but an El Niño event is not a necessary condition for determining the heavy rainfall over the MLYZR. The heavy rainfall over the MLYZR in May is always accompanied by warming of the northeastern Indian Ocean and of the northeastern South China Sea (NSCS) from April to May in the models and observations, respectively. In the models, El Niño events may promote the warming processes over the northeastern Indian Ocean, which leads to heavy rainfall in the MLYZR. However, in the real world, El Niño events are not the main reason for the warming of the NSCS, and further research on the causes of this warming is still needed.

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