Decadal Sea level Variability in the subtropical South Pacific

2020 ◽  
Author(s):  
Frauke Albrecht ◽  
Oscar Pizarro ◽  
Eduardo Zorita
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
South Pacific ◽  
Ekman Transport ◽  
Cmip5 Models ◽  
Altimetry Data ◽  
Sea Level Variability ◽  
The North

<p>Observational altimetry data and data of 18 phase 5 of the Coupled Model Intercomparison Project (CMIP5) are investigated to analyze decadal sea level variability for the subtropical South Pacific. The altimetry data covers the period 1993 to 2017. In order to analyze decadal variability yearly means of detrended data are considered. An Empirical Orthogonal Function (EOF) analysis of the Region 20°S to 60°S is performed in to analyze sea level variablility in the subtropics. The tropical region has been omitted in order to avoid the strong El Niño Southern Oscillation (ENSO) signal masking other subtropical variability in the analysis. The first EOF of the altimetry data shows a clear pattern with a North-South dipole explaining 30% of the variance and the corresponding time series shows a decadal periodicity. The decadal variability of this pattern is reproduced by the CMIP5 models. Analyzing model ocean circulation data show consistent decadal variability in the North-South velocity. As a possible forcing zonal (westerly) surface winds are analyzed. Their pattern confirm Ekman transport to the North (South) in the lower (higher) latitudes, leading to a convergence zone and therefore explaining the sea level rise as seen in the EOF pattern, consistently with the Ekman transport a deep compensatory poleward flow is observed.</p>

Decadal Sea Level Variability in the South Pacific in a Global Eddy-Resolving Ocean Model Hindcast

2008 ◽  
Vol 38 (8) ◽  
pp. 1731-1747 ◽  
Author(s):  
Yoshi N. Sasaki ◽  
Shoshiro Minobe ◽  
Niklas Schneider ◽  
Takashi Kagimoto ◽  
Masami Nonaka ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
General Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Circulation Model ◽  
South Pacific ◽  
The South ◽  
Sea Level Variability ◽  
The Impact

Abstract Sea level variability and related oceanic changes in the South Pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy-resolving ocean general circulation model (OGCM) for the Earth Simulator (OFES), along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992. The first empirical orthogonal function mode of sea level anomalies (SLAs) of OFES exhibits broad positive SLAs over the central and western South Pacific. The corresponding principal component indicates roughly stable high, low, and high SLAs, separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s, consistent with tide gauge and satellite observations. These decadal changes are accompanied by circulation changes of the subtropical gyre at 1000-m depth, and changes of upper-ocean zonal current and eddy activity around the Tasman Front. In general agreement with previous related studies, it is found that sea level variations in the Tasman Sea can be explained by propagation of long baroclinic Rossby waves forced by wind stress curl anomalies, if the impact of New Zealand is taken into account. The corresponding atmospheric variations are associated with decadal variability of El Niño–Southern Oscillation (ENSO). Thus, decadal sea level variability in the western and central South Pacific in the past three and half decades and decadal ENSO variability are likely to be connected. The sea level rise in the 1990s, which attracted much attention in relation to the global warming, is likely associated with the decadal cooling in the tropical Pacific.

Tropical Pacific Decadal Variability and ENSO Precursor in CMIP5 Models

2021 ◽  
Vol 34 (3) ◽  
pp. 1023-1045
Author(s):  
Yingying Zhao ◽  
Emanuele Di Lorenzo ◽  
Daoxun Sun ◽  
Samantha Stevenson
Keyword(s):  
Decadal Variability ◽  
South Pacific ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
The North ◽  
Enso Teleconnections ◽  
Pacific Decadal Variability ◽  
Basin Scale ◽  
The Tropics ◽  
North And South

AbstractObservational analyses suggest that a significant fraction of the tropical Pacific decadal variability (TPDV) (~60%–70%) is energized by the combined action of extratropical precursors of El Niño–Southern Oscillation (ENSO) originating from the North and South Pacific. Specifically, the growth and decay of the basin-scale TPDV pattern (time scale = ~1.5–2 years) is linked to the following sequence: ENSO precursors (extratropics, growth phase) → ENSO (tropics, peak phase) → ENSO successors (extratropics, decay phase) resulting from ENSO teleconnections. This sequence of teleconnections is an important physical basis for Pacific climate predictability. Here we examine the TPDV and its connection to extratropical dynamics in 20 models from phase 5 of the Coupled Model Intercomparison Project (CMIP). We find that most models (~80%) can simulate the observed spatial pattern (R > 0.6) and frequency characteristics of the TPDV. In 12 models, more than 65% of the basinwide Pacific decadal variability (PDV) originates from TPDV, which is comparable with observations (~70%). However, despite reproducing the basic spatial and temporal statistics, models underestimate the influence of the North and South Pacific ENSO precursors to the TPDV, and most of the models’ TPDV originates in the tropics. Only 35%–40% of the models reproduce the observed extratropical ENSO precursor patterns (R > 0.5). Models with a better representation of the ENSO precursors show 1) better basin-scale signatures of TPDV and 2) stronger ENSO teleconnections from/to the tropics that are consistent with observations. These results suggest that better representation of ENSO precursor dynamics in CMIP may lead to improved Pacific decadal variability dynamics and predictability.

scholarly journals The Difference of Sea Level Variability by Steric Height and Altimetry in the North Pacific

2020 ◽  
Vol 12 (3) ◽  
pp. 379
Author(s):  
Qianran Zhang ◽  
Fangjie Yu ◽  
Ge Chen
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
North Pacific ◽  
Two Dimensions ◽  
Sea Level Variability ◽  
The North ◽  
Relationship Of ◽  
Along Track ◽  
The Relationship ◽  
The North Pacific

Sea level variability, which is less than ~100 km in scale, is important in upper-ocean circulation dynamics and is difficult to observe by existing altimetry observations; thus, interferometric altimetry, which effectively provides high-resolution observations over two swaths, was developed. However, validating the sea level variability in two dimensions is a difficult task. In theory, using the steric method to validate height variability in different pixels is feasible and has already been proven by modelled and altimetry gridded data. In this paper, we use Argo data around a typical mesoscale eddy and altimetry along-track data in the North Pacific to analyze the relationship between steric data and along-track data (SD-AD) at two points, which indicates the feasibility of the steric method. We also analyzed the result of SD-AD by the relationship of the distance of the Argo and the satellite in Point 1 (P1) and Point 2 (P2), the relationship of two Argo positions, the relationship of the distance between Argo positions and the eddy center and the relationship of the wind. The results showed that the relationship of the SD-AD can reach a correlation coefficient of ~0.98, the root mean square deviation (RMSD) was ~1.8 cm, the bias was ~0.6 cm. This proved that it is feasible to validate interferometric altimetry data using the steric method under these conditions.

scholarly journals Subtropical Forcing of Tropical Pacific Climate and Decadal ENSO Modulation

2008 ◽  
Vol 21 (18) ◽  
pp. 4691-4709 ◽  
Author(s):  
Daniela Matei ◽  
Noel Keenlyside ◽  
Mojib Latif ◽  
Johann Jungclaus
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Circulation Model ◽  
South Pacific ◽  
Tropical Pacific ◽  
Ocean Dynamics ◽  
The North ◽  
The North Pacific

Abstract The relative impact of the subtropical North and South Pacific Oceans on the tropical Pacific climate mean state and variability is estimated using an ocean–atmosphere–sea ice coupled general circulation model. Tailored experiments are performed in which the model is forced by idealized sea surface temperature anomalies (SSTAs) in the subtropics of both hemispheres. The main results of this study suggest that subtropical South Pacific climate variations play a dominant role in tropical Pacific decadal variability and in the decadal modulation of El Niño–Southern Oscillation (ENSO). In response to a 2°C warming in the subtropical South Pacific, the equatorial Pacific SST increases by about 0.6°C, approximately 65% larger than the change in the North Pacific experiment. The subtropics affect equatorial SST mainly through atmosphere–mixed layer interactions in the South Pacific experiments; the response is mostly accomplished within a decade. The “oceanic tunnel” dominates in the North Pacific experiments; the response takes at least 100 yr to be accomplished. Similar sensitivity experiments conducted with the stand-alone atmosphere model showed that both air–sea interactions and ocean dynamics are crucial in shaping the tropical climate response. The statistics of ENSO exhibit significant changes in amplitude and frequency in response to a warming/cooling of the subtropical South Pacific: a 2°C warming (cooling) of subtropical South Pacific SST reduces (increases) the interannual standard deviation by about 30% (20%) and shortens (lengthens) the ENSO period. The simulated changes in the equatorial zonal SST gradient are the main contributor to the modulation of ENSO variability. The simulated intensification (weakening) of the annual cycle in response to an enhanced warming (cooling) in subtropical South Pacific partly explains the shifts in frequency, but may also lead to a weaker (stronger) ENSO. The subtropical North Pacific thermal forcing did not change the statistical properties of ENSO as strongly.

scholarly journals Sea-state contributions to sea-level variability in the European Seas

2020 ◽  
Vol 70 (12) ◽  
pp. 1547-1569
Author(s):  
Antonio Bonaduce ◽  
Joanna Staneva ◽  
Sebastian Grayek ◽  
Jean-Raymond Bidlot ◽  
Øyvind Breivik
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Ocean Circulation ◽  
Ocean Wave ◽  
Sea State ◽  
Sea Level Variability ◽  
The North ◽  
The North Sea ◽  
The Baltic ◽  
Wave Induced

AbstractThe contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (> 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.

Annual and inter-annual sea-level variability from coastal altimetry and tide gauge data

2021 ◽  
Author(s):  
Anara Kudabayeva ◽  
Michael Schindelegger ◽  
Rui M. Ponte ◽  
Bernd Uebbing
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
Tide Gauge ◽  
Low Frequency ◽  
Altimeter Data ◽  
Altimetry Data ◽  
Tide Gauges ◽  
Sea Level Variability ◽  
Short Scale ◽  
The Impact

<p> <span>Accurate long-term measurements of coastal sea level are fundamental for understanding changes in ocean circulation and assessing the impact of low-frequency sea-level variability on, e.g., near-shore ecosystems, groundwater dynamics, and coastal flooding. However, tide gauges are sparsely distributed in space and the extent to which satellite altimetry data can be used to infer the complex patterns of sea level near the coast is a subject of debate. Here, we revisit earlier attempts of connecting tide gauge and altimetry observations of low-frequency sea-level changes across the coastal zone. Our interest lies both in short-scale spatial structures indicative of dynamic decoupling between coastal areas and the deep ocean, and in the benefits of using a reprocessed, coastal altimetry product (X-TRACK) for the analysis. The mean annual cycle is chosen as a first benchmark and more than 200 globally distributed tide gauges are examined. We compute statistics between tide gauge and along-track altimeter series within spatial radii of 20 km (“coastal”) and 134 km of the tide gauge location, and additionally split altimetry data inside the 134-km circle into “shallow” and “deep” groups relative to the 200-m isobaths. Globally averaged RMS (root-mean-square) differences in the “coastal” and “shallow” categories are 1.9 and 2.4 cm for the X-TRACK product, somewhat lower than the corresponding values from the non-optimized Integrated Multi-Mission Ocean Altimeter Data for Climate Research Version 4.2 (2.3 and 2.6 cm). Examination of inter-annual sea-level variability from 1993 to 2019 is underway, with initial focus on regions where poor correspondence between satellite and tide gauge sea-level estimates has been noted in the past (e.g., US East Coast and western South America). At most locations analyzed so far, RMS differences decrease and correlations improve as one approaches the coast along the satellite tracks. However, the X-TRACK estimates tend to become erratic within 20–30 km from the tide gauge, suggesting that the usability of classical nadir altimetry measurements for studying short-scale coastal dynamics is still limited despite ongoing reprocessing efforts.</span></p>

Mechanism of Interannual Variability of Ocean Bottom Pressure in the South Pacific

2021 ◽  
Author(s):  
Jianhuang Qin ◽  
Xuhua Cheng ◽  
Chengcheng Yang ◽  
Niansen Ou ◽  
Xiaoqin Xiong
Keyword(s):  
Sea Level ◽  
Southern Oscillation ◽  
South Pacific ◽  
Ekman Transport ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
The South ◽  
Austral Spring ◽  
Ocean Bottom Pressure ◽  
Southeastern Pacific

Abstract The study of ocean bottom pressure (OBP) is useful for understanding the barotropic processes variability that contribute to sea level rise. Previous studies have reported the strong OBP anomalies in the Southern Ocean on different time scales. In this study, the characteristic and mechanisms of the energetic interannual OBP variability in the southeastern Pacific are examined using 14 years of GRACE data. It is found that the OBP anomalies are positive (negative) related to the convergence (divergence) of Ekman transport forced by local winds variability. The sea level pressure (SLP) anomalies shows a wavenumber-3 structure in the high latitude of the South Pacific, which benefits a strong and persistent anticyclone over the southeastern Pacific, leading to the positive OBP anomalies there. Such SLP anomalies are similar to the second Pacific-South American (PSA2). Moreover, El Niño–Southern Oscillation (ENSO) plays an important role in the austral spring (August-November) OBP variability and leads the austral autumn (March-June) OBP variability by 1 season. These results highlight the influence of atmospheric variability on OBP anomalies and are validated by a mass conservation (non-Boussinesq) ocean model, which is expected to not only better understanding of OBP mechanisms in a longer time, but also predict OBP variation in the global scale.

scholarly journals Sea-state contributions to sea-level variability in the European Seas

2021 ◽  
Author(s):  
Antonio Bonaduce ◽  
Joanna Staneva ◽  
Sebastian Grayek ◽  
Jean-Raymond Bidlot ◽  
Øyvind Breivik
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Ocean Circulation ◽  
Ocean Wave ◽  
Sea State ◽  
Sea Level Variability ◽  
The North ◽  
The North Sea ◽  
The Baltic ◽  
Wave Induced

<p>The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (> 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.</p>

scholarly journals Mean sea level variability in the North Sea: Processes and implications

2014 ◽  
Vol 119 (10) ◽  
pp. n/a-n/a ◽  
Author(s):  
Sönke Dangendorf ◽  
Francisco M. Calafat ◽  
Arne Arns ◽  
Thomas Wahl ◽  
Ivan D. Haigh ◽  
...  
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Sea Level Variability ◽  
Mean Sea Level ◽  
The North ◽  
The North Sea ◽  
Mean Sea Level Variability

scholarly journals Structure of ocean circulation between the Galápagos Islands and Ecuador

2013 ◽  
Vol 33 ◽  
pp. 3-12 ◽  
Author(s):  
C. Collins ◽  
A. Mascarenhas ◽  
R. Martinez
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Galapagos Islands ◽  
Surface Flow ◽  
Climate Indices ◽  
Late Winter ◽  
Coastal Current ◽  
Galápagos Islands

Abstract. From 27 March to 5 April 2009, upper ocean velocities between the Galápagos Islands and Ecuador were measured using a vessel mounted ADCP. A region of possible strong cross-hemisphere exchange was observed immediately to the east of the Galápagos, where a shallow (200 m) 300 km wide northeastward surface flow transported 7–11 Sv. Underlying this strong northeastward surface current, a southward flowing undercurrent was observed which was at least 600 m thick, 100 km wide, and had an observed transport of 7–8 Sv. Next to the Ecuador coast, the shallow (< 200 m) Ecuador Coastal Current was observed to extend offshore 100 km with strongest flow, 0.33 m s−1, near the surface. Immediately to the west of the Ecuador Coastal Current, flow was directed eastward and southward into the beginnings of the Peru-Chile Countercurrent. The integral of the surface currents between the Galápagos and Ecuador agreed well with observed sea level differences. Although the correlation of the sea level differences with large scale climate indices (Niño3 and the Southern Oscillation Index) was significant, more than half of the sea level variability was not explained. Seasonal variability of the sea level difference indicated that sea level was 2 cm higher at the Galápagos during late winter and early spring, which could be associated with the pattern of northward surface flows observed by R/V Knorr.

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