scholarly journals Observed equatorial Rossby waves and ENSO-related warm water volume changes in the equatorial Pacific Ocean

2008 ◽  
Vol 113 (C6) ◽  
Author(s):  
Christelle Bosc ◽  
Thierry Delcroix
Keyword(s):  
Pacific Ocean ◽  
Rossby Waves ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Equatorial Pacific Ocean ◽  
Volume Changes ◽  
Warm Water Volume ◽  
Equatorial Rossby Waves

scholarly journals Effect of the Variability of Wind Forcing on ENSO Simulation in an OGCM: Case of Canonical and Protracted Event

2021 ◽  
Author(s):  
Anika Arora
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
Ocean Model ◽  
Equatorial Pacific ◽  
Wind Forcing ◽  
Water Volume ◽  
Equatorial Pacific Ocean ◽  
Warm Water Volume

Abstract This study is an attempt to understand the onset and evolution of canonical El Niño (~ 18–24 months; CE) and protracted El Niño (> greater than 3 years; PE) compared to the normal state (NS) in an ocean model. Indo-Pacific warm pool indicates higher values of SST before the onset of strong canonical El Niño compared to the normal state and protracted El Niño. The ocean model used in the study shows systematic SST bias in the Indo-Pacific Ocean with higher (cooler) values of temperature in western (eastern) Pacific during NS, CE, and PE exhibiting La Niña like conditions. The ocean model exhibits deeper thermocline depth in the western equatorial Pacific Ocean (PO) during PE and CE compared to NS indicating higher values of heat content (warm water volume). Despite the presence of higher warm water volume in the western PO before the onset of El Niño, the difference in the variability of surface wind forcing during the preceding months determines the type of El Niño. The interplay of surface wind forcing among the NS, PE, and CE states without altering the ocean state can modify the subsurface propagation in the equatorial Pacific Ocean. A change in longitudinal extent of upwelling Kelvin waves towards eastern PO along with the change in surface wind forcing decides the fate of El Niño in the eastern Pacific.

scholarly journals Effect of the Variability of Wind Forcing on ENSO Simulation in an OGCM: Case of Canonical and Protracted Event

2021 ◽  
Author(s):  
Anika Arora
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
Ocean Model ◽  
Equatorial Pacific ◽  
Wind Forcing ◽  
Water Volume ◽  
Equatorial Pacific Ocean ◽  
Warm Water Volume

Abstract This study is an attempt to understand the onset and evolution of canonical El Niño (~ 18–24 months; CE) and protracted El Niño (> greater than 3 years; PE) compared to the normal state (NS) in an ocean model. Indo-Pacific warm pool indicates higher values of SST before the onset of strong canonical El Niño compared to the normal state and protracted El Niño. The ocean model used in the study shows systematic SST bias in the Indo-Pacific Ocean with higher (cooler) values of temperature in western (eastern) Pacific during NS, CE, and PE exhibiting La Niña like conditions. The ocean model exhibits deeper thermocline depth in the western equatorial Pacific Ocean (PO) during PE and CE compared to NS indicating higher values of heat content (warm water volume). Despite the presence of higher warm water volume in the western PO before the onset of El Niño, the difference in the variability of surface wind forcing during the preceding months determines the type of El Niño. The interplay of surface wind forcing among the NS, PE, and CE states without altering the ocean state can modify the subsurface propagation in the equatorial Pacific Ocean. A change in longitudinal extent of upwelling Kelvin waves towards eastern PO along with the change in surface wind forcing decides the fate of El Niño in the eastern Pacific.

Ocean Response to Wind Variations, Warm Water Volume, and Simple Models of ENSO in the Low-Frequency Approximation

2010 ◽  
Vol 23 (14) ◽  
pp. 3855-3873 ◽  
Author(s):  
Alexey V. Fedorov
Keyword(s):  
Low Frequency ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Thermocline Depth ◽  
Phase Lag ◽  
Eastern Equatorial Pacific ◽  
The Pacific ◽  
Warm Water Volume ◽  
Frequency Approximation

Abstract Physical processes that control ENSO are relatively fast. For instance, it takes only several months for a Kelvin wave to cross the Pacific basin (Tk ≈ 2 months), while Rossby waves travel the same distance in about half a year. Compared to such short time scales, the typical periodicity of El Niño is much longer (T ≈ 2–7 yr). Thus, ENSO is fundamentally a low-frequency phenomenon in the context of these faster processes. Here, the author takes advantage of this fact and uses the smallness of the ratio ɛk = Tk/T to expand solutions of the ocean shallow-water equations into power series (the actual parameter of expansion also includes the oceanic damping rate). Using such an expansion, referred to here as the low-frequency approximation, the author relates thermocline depth anomalies to temperature variations in the eastern equatorial Pacific via an explicit integral operator. This allows a simplified formulation of ENSO dynamics based on an integro-differential equation. Within this formulation, the author shows how the interplay between wind stress curl and oceanic damping rates affects 1) the amplitude and periodicity of El Niño and 2) the phase lag between variations in the equatorial warm water volume and SST in the eastern Pacific. A simple analytical expression is derived for the phase lag. Further, applying the low-frequency approximation to the observed variations in SST, the author computes thermocline depth anomalies in the western and eastern equatorial Pacific to show a good agreement with the observed variations in warm water volume. Ultimately, this approach provides a rigorous framework for deriving other simple models of ENSO (the delayed and recharge oscillators), highlights the limitations of such models, and can be easily used for decadal climate variability in the Pacific.

scholarly journals One plausible reason for the change in ENSO characteristics in the 2000s

2013 ◽  
Vol 10 (4) ◽  
pp. 951-984
Author(s):  
V. N. Stepanov
Keyword(s):  
Southern Ocean ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Atmospheric Conditions ◽  
Enso Events ◽  
Wind Variability ◽  
Western Equatorial Pacific ◽  
Warm Water Volume ◽  
The Tropics

Abstract. It is well known that El Niño Southern Oscillation (ENSO) causes floods, droughts and the collapse of fisheries, therefore forecasting of ENSO is an important task in climate researches. Variations in the equatorial warm water volume of the tropical Pacific and wind variability in the western equatorial Pacific has been considered to be a good ENSO predictor. However, in the 2000s, the interrelationship between these two characteristics and ENSO onsets became weak. This article attempts to find some plausible explanation for this. The results presented here demonstrate a possible link between the variability of atmospheric conditions over the Southern Ocean and their impact on the ocean circulation leading to the amplifying/triggering of ENSO events. It is shown that the variability of the atmospheric conditions upstream of Drake Passage can strongly influence ENSO events. The interrelationship between ENSO and variability in the equatorial warm water volume of the equatorial Pacific, together with wind variability in the western equatorial Pacific has recently weakened. It can be explained by the fact that the process occurred in the Southern Ocean recently became a major contributor amplifying ENSO events (in comparison with the processes of interaction between the atmosphere and the ocean in the tropics of the Pacific). Likely it is due to a warmer ocean state observed from the end of the 1990s that led to smaller atmospheric variability in the tropics and insignificant their changes in the Southern Ocean.

scholarly journals On the Physics of the Warm Water Volume and El Niño/La Niña Predictability

2019 ◽  
Vol 49 (6) ◽  
pp. 1541-1560 ◽  
Author(s):  
Allan J. Clarke ◽  
Xiaolin Zhang
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Equatorial Pacific ◽  
La Niña ◽  
Warm Water ◽  
Water Volume ◽  
La Nina ◽  
Eastern Equatorial Pacific ◽  
Warm Water Volume

AbstractPrevious work has shown that warm water volume (WWV), usually defined as the volume of equatorial Pacific warm water above the 20°C isotherm between 5°S and 5°N, leads El Niño. In contrast to previous discharge–recharge oscillator theory, here it is shown that anomalous zonal flow acceleration right at the equator and the movement of the equatorial warm pool are crucial to understanding WWV–El Niño dynamics and the ability of WWV to predict ENSO. Specifically, after westerly equatorial wind anomalies in a coupled ocean–atmosphere instability push the warm pool eastward during El Niño, the westerly anomalies follow the warmest water south of the equator in the Southern Hemisphere summer in December–February. With the wind forcing that causes El Niño in the eastern Pacific removed, the eastern equatorial Pacific sea level and thermocline anomalies decrease. Through long Rossby wave dynamics this decrease results in an anomalous westward equatorial flow that tends to push the warm pool westward and often results in the generation of a La Niña during March–June. The anomalously negative eastern equatorial Pacific sea level typically does not change as much during La Niña, the negative feedback is not as strong, and El Niños tend to not follow La Niñas the next year. This El Niño/La Niña asymmetry is seen in the WWV/El Niño phase diagram and decreased predictability during “La Niña–like” decades.

scholarly journals Interdecadal Sea Surface Temperature Variability in the Equatorial Pacific Ocean. Part I: The Role of Off-Equatorial Wind Stresses and Oceanic Rossby Waves

2007 ◽  
Vol 20 (11) ◽  
pp. 2643-2658 ◽  
Author(s):  
Shayne McGregor ◽  
Neil J. Holbrook ◽  
Scott B. Power
Keyword(s):  
Pacific Ocean ◽  
Wind Stress ◽  
Rossby Waves ◽  
Wave Reflection ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Thermocline Depth ◽  
Equatorial Pacific Ocean ◽  
Equatorial Thermocline ◽  
The Western Pacific

Abstract The Australian Bureau of Meteorology Research Centre CGCM and a linear first baroclinic-mode ocean shallow-water model (SWM) are used to investigate ocean dynamic forcing mechanisms of the equatorial Pacific Ocean interdecadal sea surface temperature (SST) variability. An EOF analysis of the 13-yr low-pass Butterworth-filtered SST anomalies from a century-time-scale CGCM simulation reveals an SST anomaly spatial pattern and time variability consistent with the interdecadal Pacific oscillation. Results from an SWM simulation forced with wind stresses from the CGCM simulation are shown to compare well with the CGCM, and as such the SWM is then used to investigate the roles of “uncoupled” equatorial wind stress forcing, off-equatorial wind stress forcing (OffEqWF), and Rossby wave reflection at the western Pacific Ocean boundary, on the decadal equatorial thermocline depth anomalies. Equatorial Pacific wind stresses are shown to explain a large proportion of the overall variance in the equatorial thermocline depth anomalies. However, OffEqWF beyond 12.5° latitude produces an interdecadal signature in the Niño-4 (Niño-3) region that explains approximately 10% (1.5%) of the filtered control simulation variance. Rossby wave reflection at the western Pacific boundary is shown to underpin the OffEqWF contribution to these equatorial anomalies. The implications of this result for the predictability of the decadal variations of thermocline depth are investigated with results showing that OffEqWF generates an equatorial response in the Niño-3 region up to 3 yr after the wind stress forcing is switched off. Further, a statistically significant correlation is found between thermocline depth anomalies in the off-equatorial zone and the Niño-3 region, with the Niño-3 region lagging by approximately 2 yr. The authors conclude that there is potential predictability of the OffEqWF equatorial thermocline depth anomalies with lead times of up to 3 yr when taking into account the amplitudes and locations of off-equatorial region Rossby waves.

scholarly journals Mechanisms controlling warm water volume interannual variations in the equatorial Pacific: diabatic versus adiabatic processes

2011 ◽  
Vol 38 (5-6) ◽  
pp. 1031-1046 ◽  
Author(s):  
M. Lengaigne ◽  
U. Hausmann ◽  
G. Madec ◽  
C. Menkes ◽  
J. Vialard ◽  
...  
Keyword(s):  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Interannual Variations ◽  
Warm Water Volume ◽  
Adiabatic Processes
Sign in / Sign up

Export Citation Format

Share Document