scholarly journals Dynamics of Upwelling Annual Cycle in the Equatorial Pacific Ocean

2019 ◽  
Vol 11 (18) ◽  
pp. 5038
Author(s):  
Li-Chiao Wang ◽  
Jia-Yuh Yu
Keyword(s):  
Annual Cycle ◽  
Equatorial Pacific ◽  
Thermocline Depth ◽  
Equatorial Pacific Ocean ◽  
Equatorial Atlantic ◽  
Local Wind ◽  
Simple Formulation ◽  
Annual Cycles ◽  
Equatorial Thermocline ◽  
Ekman Upwelling

A recent work proposed a simple theory based on the framework of Zebiak–Cane (ZC) ocean model, and successfully characterized the equatorial Atlantic upwelling annual cycle as a combination of the local wind-driven Ekman upwelling and nonlocal wind-driven wave upwelling. In the present work, utilizing the same simple framework, we examined the fidelity of the upwelling Pacific annual cycle using observations and simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). We demonstrated that the theoretical upwelling annual cycles generally match the original upwelling annual cycles in the equatorial Pacific in both observations and CMIP5 simulations. Therefore, this simple formulation can be used to represent the upwelling annual cycle in the equatorial Pacific. Observationally, the equatorial Pacific upwelling annual cycle is dominated by the local wind-driven Ekman upwelling, while the remote wave upwelling is confined near the eastern boundary with little contribution. In CMIP5 simulations, though the theoretical-reconstructed upwelling well-reproduces the original upwelling, the contribution is totally different compared to the observation. The wave upwelling serves as the main contributor instead of the Ekman upwelling. We further demonstrated that such discrepancy is attributable to the bias of the central to eastern equatorial thermocline depth patterns. This amplified, westward-shift wave upwelling weakened the impacts of the Ekman upwelling, and contributes to the entire Pacific equatorial upwelling annual cycle substantially. This implies that a realistic simulation of the equatorial Pacific upwelling annual cycle in models is very sensitive to the careful simulation of the equatorial thermocline depth annual evolutions.

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.

Inter-basin interactions between the Pacific and Atlantic Oceans depending on the phase of Pacific decadal Oscillation and Atlantic multi-decadal oscillation

2021 ◽  
pp. 1-38
Keyword(s):  
Pacific Ocean ◽  
Atlantic Ocean ◽  
Pacific Decadal Oscillation ◽  
Walker Circulation ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Equatorial Atlantic ◽  
The Pacific ◽  
Equatorial Atlantic Ocean ◽  
Relationship Of

Abstract The authors investigated the inter-basin interactions between the Pacific and Atlantic Oceans depending on the phase relationship of Pacific decadal oscillation (PDO)/Atlantic multi-decadal oscillation (AMO) based on observations and idealized model experiments. When the AMO and the PDO are in-phase (i.e., +PDO/+AMO or −PDO/-AMO), the Pacific Ocean regulates the SST anomalies in the equatorial Atlantic Ocean with altering a Walker circulation. During this period, there is a negative SST-precipitation relationship in the equatorial Atlantic Ocean where the atmosphere forces the ocean. In contrast, when they are out-of-phase (i.e., either +PDO/-AMO or −PDO/+AMO), the Atlantic Ocean influences the equatorial Pacific Ocean by modifying Walker circulation, resulting in a westward shift of a center of convective forcing in the equatorial Pacific Ocean compared to that during an inphase relationship of PDO/AMO. During this period, a positive SST-precipitation relationship is dominant in the equatorial Atlantic Ocean where the ocean forces the atmosphere. To verify this result, we conducted pacemaker experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM3). Model results supported our findings obtained from the observations. We infer that the characteristics of the Pacific-Atlantic inter-basin interactions depend on whether the PDO and AMO phases are either in-phase or out of phase.

scholarly journals Influence of Recent Stratification Changes on ENSO Stability in a Conceptual Model of the Equatorial Pacific

2013 ◽  
Vol 26 (13) ◽  
pp. 4790-4802 ◽  
Author(s):  
Sulian Thual ◽  
Boris Dewitte ◽  
Soon-Il An ◽  
Serena Illig ◽  
Nadia Ayoub
Keyword(s):  
Linear Stability ◽  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Equatorial Pacific ◽  
Thermocline Depth ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Equatorial Pacific Ocean ◽  
Decadal Modulation ◽  
The Mean

Abstract Changes in the mean circulation of the equatorial Pacific Ocean partly control the strong decadal modulation of El Niño–Southern Oscillation (ENSO). This relationship is considered from the linear stability of a conceptual recharge/discharge model with parameters tuned from the observed mean state. Whereas decadal changes in the mean thermocline depth alone are usually considered in conceptual ENSO models, here focus is given to decadal changes in the mean stratification of the entire upper ocean (e.g., the mean thermocline depth, intensity, and thickness). Those stratification changes modify the projection of wind stress forcing momentum onto the gravest ocean baroclinic modes. Their influence on the simulated frequency and growth rate is comparable in intensity to the one of usual thermodynamic and atmospheric feedbacks, while they have here a secondary effect on the spatial structure and propagation of SST anomalies. This sensitivity is evidenced in particular for the climate shift of the 1970s in the Simple Ocean Data Assimilation (SODA) dataset, as well as in a preindustrial simulation of the Geophysical Fluid Dynamics Laboratory (GFDL) model showing stratification changes similar to the ones after 2000. Despite limitations of the linear stability approach, conclusions on the sensitivity to stratification may be extended to interpret the modulation and diversity of ENSO in observations and in general circulation models.

scholarly journals Subduction of South Pacific Tropical Water and Its Equatorward Pathways as Shown by a Simulated Passive Tracer*

2013 ◽  
Vol 43 (8) ◽  
pp. 1551-1565 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao ◽  
Rana A. Fine
Keyword(s):  
South Pacific ◽  
Equatorial Region ◽  
Equatorial Pacific ◽  
Western Boundary ◽  
Passive Tracer ◽  
Tropical Water ◽  
South Pacific Ocean ◽  
Equal Importance ◽  
Equatorial Thermocline ◽  
South Pacific Tropical Water

Abstract This study investigates the subduction of South Pacific Tropical Water (SPTW) and its equatorward pathways using a simulated passive tracer of the consortium Estimating the Circulation & Climate of the Ocean (ECCO). The results show that approximately 5.8 Sv (1 Sv ≡ 106 m3 s−1) of the SPTW is formed in the subtropical South Pacific Ocean within the density range between 24.0 and 25.0 kg m−3, of which about 87% is due to vertical pumping and 13% is due to lateral induction, comparing reasonably well with estimates from climatological data. Once subducted, most SPTW spreads in the subtropical South Pacific. Because of the presence of mixing, some portion of the water is transformed, and its tracer-weighted density steadily increases from an initial value of 24.4 to nearly 25.0 kg m−3 after 13 years of integration. Approximately 42% of the water makes its way into the equatorial Pacific, either through the western boundary or interior pathway. The two equatorward pathways are essentially of equal importance. A large (~70%) portion of the SPTW entering the equatorial region resurfaces in the central equatorial Pacific. The potential impacts of the resurfacing SPTW on the equatorial thermocline and surface stratification are discussed.

Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean

Nature ◽  
1994 ◽  
Vol 371 (6493) ◽  
pp. 123-129 ◽  
Author(s):  
J. H. Martin ◽  
K. H. Coale ◽  
K. S. Johnson ◽  
S. E. Fitzwater ◽  
R. M. Gordon ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean

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.

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