scholarly journals El Niño Effects and Upwelling off South Australia

2007 ◽  
Vol 37 (10) ◽  
pp. 2458-2477 ◽  
Author(s):  
John F. Middleton ◽  
Craig Arthur ◽  
Paul Van Ruth ◽  
Tim M. Ward ◽  
Julie L. McClean ◽  
...  
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
South Australia ◽  
Ocean Model ◽  
Global Ocean ◽  
Shelf Edge ◽  
The West ◽  
Enso Events

Abstract To determine the possible importance of ENSO events along the coast of South Australia, an exploratory analysis is made of meteorological and oceanographic data and output from a global ocean model. Long time series of coastal sea level and wind stress are used to show that while upwelling favorable winds have been more persistent since 1982, ENSO events (i) are largely driven by signals from the west Pacific Ocean shelf/slope waveguide and not local meteorological conditions, (ii) can account for 10-cm changes in sea level, and (iii) together with wind stress, explain 62% of the variance of annual-averaged sea level. Thus, both local winds and remote forcing from the west Pacific are likely important to the low-frequency shelf edge circulation. Evidence also suggests that, since 1983, wintertime downwelling during the onset of an El Niño is reduced and the following summertime upwelling is enhanced. In situ data show that during the 1998 and 2003 El Niño events anomalously cold (10.5°–11.5°C) water is found at depths of 60–120 m and is more than two standard deviations cooler than the mean. A regression showed that averaged sea level can provide a statistically significant proxy for these subsurface temperature changes and indicates a 2.2°C decrease in temperature for the 10-cm decrease in sea level that was driven by the 1998 El Niño event. Limited current- meter observations, long sea level records, and output from a global ocean model were also examined and provide support for the hypothesis that El Niño events substantially reduce wintertime (but not summertime) shelf-edge currents. Further research to confirm this asymmetric response and its cause is required.

scholarly journals El Niño, La Niña, and the global sea level budget

Ocean Science ◽  
2016 ◽  
Vol 12 (6) ◽  
pp. 1165-1177 ◽  
Author(s):  
Christopher G. Piecuch ◽  
Katherine J. Quinn
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Hydrological Cycle ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Global Ocean ◽  
Surface Warming ◽  
Enso Events ◽  
The Pacific

Abstract. Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño–Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth's hydrological cycle and radiation imbalance.

scholarly journals A Mechanistic Analysis of Tropical Pacific Dynamic Sea Level in GFDL-OM4 under OMIP-I and OMIP-II Forcings

2020 ◽  
Author(s):  
Chia-Wei Hsu ◽  
Jianjun Yin ◽  
Stephen M. Griffies ◽  
Raphael Dussin
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Global Ocean ◽  
Eastern Tropical Pacific ◽  
The Core ◽  
Mean State ◽  
Dynamic Sea Level

Abstract. The sea level over the tropical Pacific is a key indicator reflecting vertically integrated heat distribution over the ocean. Here we use the Geophysical Fluid Dynamics Laboratory OM4 (GFDL-OM4) global ocean-sea ice model forced by both the CORE and JRA55-do atmospheric states (OMIP-I and OMIP-II) to evaluate the model performance and biases compared against available observations. We find persisting mean state dynamic sea level (DSL) bias along 9° N even with updated wind forcing in JRA55-do relative to CORE. The mean state bias is related to biases in wind stress forcing and geostrophic currents in the 4° N to 9° N latitudinal band. The simulation forced by JRA55-do significantly reduces the bias in DSL trend over the northern tropical Pacific relative to CORE. In the CORE forcing, the anomalous westerly wind trend in the eastern tropical Pacific causes an underestimated DSL trend across the entire Pacific basin along 10° N. The simulation forced by JRA55-do significantly reduces the bias in DSL trend over the northern tropical Pacific relative to CORE. We also identify a bias in the easterly wind trend along 20° N in both JRA55-do and CORE, thus motivating future improvement. In JRA55-do, an accurate Rossby wave initiated in the eastern tropical Pacific at seasonal time scale corrects a biased seasonal variability of the northern equatorial counter-current in the CORE simulation. Both CORE and JRA55-do generate realistic DSL variation during El Nino. We find an asymmetry in the DSL pattern on two sides of the equator is strongly related to wind stress curl that follows the sea level pressure evolution during El Niño.

scholarly journals On the Role of Westerly Wind Anomalies in the Development of the 1982–1983 El Niño

2021 ◽  
Author(s):  
David J. Webb
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Initial Conditions ◽  
El Nino ◽  
Ocean Model ◽  
Global Ocean ◽  
Westerly Wind ◽  
The North ◽  
North Equatorial Counter Current ◽  
Counter Current

Abstract. A recent study of two strong El Niños highlighted the potential importance of a region of low sea level that developed in the western equatorial Pacific prior to the El Niños of 1982–1983 and 1997–1998. Here the cause of the low sea level in 1982 is investigated using a series of runs of a global ocean model with different wind fields and initial conditions. The results indicate that the low sea level was due to the increased wind shear that developed just north of the Equator during 1982. This generated Ekman divergence at the latitudes of the North Equatorial Trough, raising the underlying density surfaces and increasing the depth of the trough. This also increased the strength of the North Equatorial Counter Current which lies on the southern slope of the trough. The anomalous westerly winds associated with Madden Julian Oscillations are often held responsible for triggering El Niños through the generation of westerly wind bursts and the resulting equatorial Kelvin waves in the ocean. However if Webb (2018) is correct, the present results imply that a different physical process was involved in which Ekman divergence due to the same winds, increased the heat transported by the North Equatorial Counter Current early in the year and ultimately caused the strong 1982–1983 El Niño.

scholarly journals El Niño, La Niña, and the global sea level budget

2016 ◽  
Author(s):  
Christopher G. Piecuch ◽  
Katherine J. Quinn
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Hydrological Cycle ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Global Ocean ◽  
Surface Warming ◽  
Enso Events ◽  
The Pacific

Abstract. Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño-Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth's hydrological cycle and radiation imbalance.

scholarly journals Extended ENSO Predictions Using a Fully Coupled Ocean–Atmosphere Model

2008 ◽  
Vol 21 (1) ◽  
pp. 84-93 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Swadhin K. Behera ◽  
Toshio Yamagata
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Ocean ◽  
Enso Events ◽  
The Past ◽  
Ocean Atmosphere ◽  
First Time ◽  
Fully Coupled

Abstract Using a fully coupled global ocean–atmosphere general circulation model assimilating only sea surface temperature, the authors found for the first time that several El Niño–Southern Oscillation (ENSO) events over the past two decades can be predicted at lead times of up to 2 yr. The El Niño condition in the 1997/98 winter can be predicted to some extent up to about a 1½-yr lead but with a weak intensity and large phase delay in the prediction of the onset of this exceptionally strong event. This is attributed to the influence of active and intensive stochastic westerly wind bursts during late 1996 to mid-1997, which are generally unpredictable at seasonal time scales. The cold signals in the 1984/85 and 1999/2000 winters during the peak phases of the past two long-lasting La Niña events are predicted well up to a 2-yr lead. Amazingly, the mild El Niño–like event of 2002/03 is also predicted well up to a 2-yr lead, suggesting a link between the prolonged El Niño and the tropical Pacific decadal variability. Seasonal climate anomalies over vast parts of the globe during specific ENSO years are also realistically predicted up to a 2-yr lead for the first time.

Observed El Niño SSTA Development and the Effects of Easterly and Westerly Wind Events in 2014/15

2017 ◽  
Vol 30 (4) ◽  
pp. 1505-1519 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Ocean Model ◽  
Equatorial Pacific ◽  
Westerly Wind ◽  
Easterly Wind ◽  
Model Studies ◽  
Wind Events ◽  
Westerly Wind Events

Abstract The unexpected halt of warm sea surface temperature anomaly (SSTA) growth in 2014 and development of a major El Niño in 2015 has drawn attention to our ability to understand and predict El Niño development. Wind stress–forced ocean model studies have satisfactorily reproduced observed equatorial Pacific SSTAs during periods when data return from the TAO/TRITON buoy network was high. Unfortunately, TAO/TRITON data return in 2014 was poor. To study 2014 SSTA development, the observed wind gaps must be filled. The hypothesis that subseasonal wind events provided the dominant driver of observed waveguide SSTA development in 2014 and 2015 is used along with the available buoy winds to construct an oceanic waveguide-wide surface stress field of westerly wind events (WWEs) and easterly wind surges (EWSs). It is found that the observed Niño-3.4 SSTA development in 2014 and 2015 can thereby be reproduced satisfactorily. Previous 2014 studies used other wind fields and reached differing conclusions about the importance of WWEs and EWSs. Experiment results herein help explain these inconsistencies, and clarify the relative importance of WWEs and EWSs. It is found that the springtime surplus of WWEs and summertime balance between WWEs and EWSs (yielding small net wind stress anomaly) accounts for the early development and midyear reversal of El Niño–like SSTA development in 2014. A strong abundance of WWEs in 2015 accounts for the rapid SSTA warming observed then. Accurately forecasting equatorial Pacific SSTA in years like 2014 and 2015 may require learning to predict WWE and EWS occurrence characteristics.

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 Wind Stress Curl and ENSO Discharge/Recharge in the Equatorial Pacific

2007 ◽  
Vol 37 (4) ◽  
pp. 1077-1091 ◽  
Author(s):  
Allan J. Clarke ◽  
Stephen Van Gorder ◽  
Giuseppe Colantuono
Keyword(s):  
Wind Stress ◽  
Positive Constant ◽  
El Niño ◽  
El Nino ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Atmospheric Convection ◽  
Wind Stress Curl ◽  
The West ◽  
West Central

Abstract Discharge and recharge of the warm water volume (WWV) above the 20°C isotherm in an equatorial Pacific Ocean box extending across the Pacific from 156°E to the eastern ocean boundary between latitudes 5°S and 5°N are key variables in ENSO dynamics. A formula linking WWV anomalies, zonally integrated wind stress curl anomalies along the northern and southern edges of the box, and flow into the western end of the box is derived and tested using monthly data since 1993. Consistent with previous work, a WWV balance can only be achieved if the 20°C isotherm surface is not a material surface; that is, warm water can pass through it. For example, during El Niño, part of the WWV anomaly entering the box is cooled so that it is less than 20°C and therefore passes out of the bottom of the box, the 20°C isotherm surface. The observations suggest that the anomalous volume passing through the 20°C isotherm is approximately the same as T ′W, the anomalous WWV entering the western end of the box. Therefore the observed WWV anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box. The curl anomaly changes the WWV both by divergent meridional flow at the edges of the box and vortex stretching; that is, the Sverdrup balance does not hold in the upper ocean. A typical amplitude for the rate of change of WWV for the 5°S–5°N box is 9.6 Sv (Sv ≡ 106 m3 s−1). The wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the El Niño index Niño-3.4 [the average sea surface temperature anomaly (SSTA) over the region 5°S–5°N, 170°–120°W] and Niño-3.4 leads minus the WWV anomaly by one-quarter of a cycle. Based on the preceding results, a simple discharge/recharge coupled ENSO model is derived. Only water warmer than about 27.5°–28°C can give rise to deep atmospheric convection, so, unlike past discharge/recharge oscillator models, the west-central rather than eastern equatorial SSTAs are emphasized. The model consists of two variables: T ′, the SSTA averaged over the region of strong ENSO air–sea interaction in the west-central Pacific equatorial strip 5°S–5°N, 156°E–140°W and D′, the 20°C isotherm depth anomaly averaged over the same region. As in the observations, T ′ lags D′ by one-quarter of a cycle; that is, ∂T ′/∂t = νD′ for some positive constant ν. Physically, when D′ > 0, the thermocline is deeper and warmer water is entrained through the base of the mixed layer, the anomalous heat flux causing ∂T ′/∂t > 0. Also, when D′ > 0, the eastward current anomaly is greater than zero and warm water is advected into the region, again causing ∂T ′/∂t > 0. Opposite effects occur for D′ < 0. A second relationship between T ′ and D′ results because the water is warm enough that T ′ causes deep atmospheric convection anomalies that drive the wind stress curl anomalies that change the heat storage ∂D′/∂t. The atmosphere responds essentially instantly to the T ′ forcing and the curl causes a discharge of WWV during El Niño (T ′ > 0) and recharge during La Niña (T ′ < 0), so ∂D′/∂t = −μT ′ for some positive constant μ. The two relationships between T ′ and D′ result in a harmonic oscillator with period 2π/νμ ≈ 51 months.

scholarly journals Global runoff over 1993–2009 estimated from coupled land-ocean-atmosphere water budgets and its relation with climate variability

2012 ◽  
Vol 9 (4) ◽  
pp. 4633-4665 ◽  
Author(s):  
S. Munier ◽  
H. Palanisamy ◽  
P. Maisongrande ◽  
A. Cazenave ◽  
E. F. Wood
Keyword(s):  
Thermal Expansion ◽  
El Niño ◽  
El Nino ◽  
Global Ocean ◽  
Climate Indices ◽  
Water Budgets ◽  
Enso Events ◽  
Ocean Mass ◽  
Ocean Atmosphere ◽  
The Difference

Abstract. Whether the global runoff (or freshwater discharge from land to the ocean) is currently increasing and the global water cycle is intensifying is still a controversial issue. Here we compute land-atmosphere and ocean-atmosphere water budgets and derive two independent estimates of the global runoff over the period 1993–2009. Water storage variations in the land, ocean and atmosphere reservoirs are estimated from different types of datasets: atmospheric reanalyses, land surface models, satellite altimetry and in situ ocean temperature data (the difference between altimetry based global mean sea level and ocean thermal expansion providing an estimate of the ocean mass component). Results for the global runoff from the two methods show a very good correlation between both estimates. More importantly, no significant trend is observed over the whole period. Besides, the global runoff appears to be clearly impacted by large-scale climate phenomena such as major ENSO events. To infer this, we compute the zonal runoff over four latitudinal bands and set up for each band a new index (Combined Runoff Index) obtained by optimization of linear combinations of various climate indices. Results show that, in particular, the intertropical and northern mid-latitude runoffs are mainly driven by ENSO and the Atlantic Multidecadal Oscillation (AMO) with opposite behavior. Indeed, the zonal runoff in the intertropical zone decreases during major El Niño events whereas it increases in the northern mid-latitudes, suggesting that water masses over land are shifted northward/southward during El Niño/La Niña. In addition to this study, we propose an innovative method to estimate the global ocean thermal expansion. The method is based on the assumption that the difference between both runoff estimates is mainly due the thermal expansion term not accounted for in the estimation of the ocean mass. Comparison of our reconstructed thermal expansion with two existing datasets shows the relevance of this new method.

scholarly journals The ENSO-Related West Pacific Sea Surface Temperature Gradient

2013 ◽  
Vol 26 (23) ◽  
pp. 9545-9562 ◽  
Author(s):  
Andrew Hoell ◽  
Chris Funk
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Central Pacific ◽  
The West ◽  
West Pacific ◽  
Enso Events ◽  
West Pacific Ocean ◽  
La Nina

El Niño–Southern Oscillation (ENSO) events are accompanied by an anomalous zonal sea surface temperature (SST) gradient over the west Pacific Ocean, defined here as the west Pacific SST gradient (WPG). The WPG is defined as the standardized difference between area-averaged SST over the central Pacific Ocean (Niño-4 region) and west Pacific Ocean (0°–10°N, 130°–150°E). While the direction of the WPG follows ENSO cycles, the magnitude of the gradient varies considerably between individual El Niño and La Niña events. In this study, El Niño and La Niña events are grouped according to the magnitude of the WPG, and tropical SST, circulations, and precipitation are examined for the period 1948–2011. Until the 1980s the WPG showed little trend as the west and central Pacific warmed at similar rates; however, the west Pacific has recently warmed faster than the central Pacific, which has resulted in an increased WPG during La Niña events. The temporal evolution and distribution of tropical Pacific SST as well as the near-surface tropical Pacific zonal wind, divergence, and vertical velocity are considerably different during ENSO events partitioned according to the strength of the WPG. Modifications to the tropical circulation, resulting in changes to Indo– west Pacific precipitation, are linked to strong and consistent circulation and precipitation modifications throughout the Northern Hemisphere during winter.

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