Upper-Ocean Circulation Anomalies of the Western Equatorial Pacific Observed in 2016 Summer

2020 ◽  
Author(s):  
Yilong Lyu
Keyword(s):  
Ocean Circulation ◽  
Rossby Waves ◽  
New Guinea ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Boreal Summer ◽  
Western Boundary ◽  
Easterly Wind ◽  
Western Equatorial Pacific ◽  
Circulation Anomalies

<p>Mooring measurements at ~140°E in the western equatorial Pacific documented greatly intensified eastward subsurface currents, which largely represents the nascent Equatorial Undercurrent (EUC), to ~67 cm s<sup>-1</sup> in boreal summer of 2016. The eastward currents occupied the entire upper 500 m, with the westward surface currents nearly diminished. Similar variations were also observed during previous El Niño events, as suggested by historical in-situ data. Further analysis combining satellite and reanalysis data reveals that the eastward currents observed at ~140°E are a component of an anomalous counterclockwise circulation straddling the equator, with westward current anomalies retroflecting near the western boundary and feeding southeastward current anomalies along New Guinea coast. A 1.5-layer reduced-gravity ocean (RGO) model is able to crudely reproduce these variations, and a hierarchy of sensitivity experiments are performed to understand the underlying dynamics. The observed circulation anomalies are largely the delayed ocean response to the strong equatorial wind anomalies over the central-to-eastern Pacific basin emerging in the mature stage of El Niño (September-April). Downwelling equatorial Rossby waves are generated by the reflection of equatorial Kelvin waves and easterly wind anomalies in the eastern Pacific. Upon reaching western Pacific, the Southern Hemisphere lobe of Rossby waves encounter the slanted New Guinea island and deflects equatorward, establishing a local sea surface height maximum near the equator and leading to the detour of westward currents flowing from the Pacific interior. Additional experiments with edited western boundary geometry confirm the importance of topography in regulating the structure of this cross-equatorial anomalous circulation.</p>

Anomalous Upper-Ocean Circulation of the Western Equatorial Pacific following El Niño Events

2020 ◽  
Vol 50 (11) ◽  
pp. 3353-3373
Author(s):  
Yilong Lyu ◽  
Yuanlong Li ◽  
Jianing Wang ◽  
Jing Duan ◽  
Xiaohui Tang ◽  
...  
Keyword(s):  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
New Guinea ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Western Boundary ◽  
Western Equatorial Pacific ◽  
Anomalous Circulation ◽  
El Niño Events

AbstractMooring measurements at ~140°E in the western equatorial Pacific Ocean documented greatly intensified eastward subsurface currents, which largely represent the nascent Equatorial Undercurrent, to ~67 cm s−1 in boreal summer of 2016. The eastward currents occupied the entire upper 500 m while the westward surface currents nearly disappeared. Historical in situ data observed similar variations after most El Niño events. Further analysis combining satellite and reanalysis data reveals that the eastward currents observed at ~140°E are a component of an anomalous counterclockwise circulation straddling the equator, with westward current anomalies retroflecting near the western boundary and feeding southeastward current anomalies along the New Guinea coast. A 1.5-layer reduced-gravity ocean model is able to crudely reproduce these variations, and a hierarchy of sensitivity experiments is performed to understand the underlying dynamics. The anomalous circulation is largely the delayed ocean response to equatorial wind anomalies over the central-to-eastern Pacific basin emerging in the mature stage of El Niño. Downwelling Rossby waves are generated by the reflection of equatorial Kelvin waves and easterly winds in the eastern Pacific. Upon reaching the western Pacific, the southern lobes of Rossby waves encounter the slanted New Guinea island and deflect to the equator, establishing a local sea surface height maximum and leading to the detour of westward currents flowing from the Pacific interior. Additional experiments with edited western boundary geometry confirm the importance of topography in regulating the structure of this cross-equatorial anomalous circulation.

scholarly journals Reducing Climatology Bias in an Ocean–Atmosphere CGCM with Improved Coupling Physics

2005 ◽  
Vol 18 (13) ◽  
pp. 2344-2360 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Erich Roeckner ◽  
Gurvan Madec ◽  
Toshio Yamagata
Keyword(s):  
Wind Stress ◽  
Surface Current ◽  
Ocean Surface ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Easterly Wind ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs. By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically. The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.

Fluctuations in Terrestrial–Marine Environments in the Western Equatorial Pacific during the Late Pleistocene

2002 ◽  
Vol 57 (1) ◽  
pp. 71-81 ◽  
Author(s):  
Hodaka Kawahata ◽  
Rena Maeda ◽  
Hideaki Ohshima
Keyword(s):  
Late Pleistocene ◽  
Accumulation Rate ◽  
Global Climate ◽  
New Guinea ◽  
Equatorial Pacific ◽  
Pollen Record ◽  
Western Equatorial Pacific ◽  
Large Heat ◽  
Pollen And Spores ◽  
Marine Environmental

AbstractLarge heat storage capacity in the western equatorial Pacific has played an important role in modulating global climate. The fluctuation in pollen and spore abundances, together with organic matter (OM) and lithogenics sedimentation, was investigated to reconstruct terrestrial and marine environmental change around New Guinea during the Late Pleistocene. Although appreciable contribution from Indonesian Maritime Continent was expected, the majority of the pollen and spore grains found in core C4402 was transported from New Guinea. Fern spores accounted for 70% (46–90%) of the total pollens and spores. Positive correlation between lithogenic content and the relative abundance of fern spores suggests that lithogenics could be derived from coastal lowland.The mass accumulation rate (MAR) of pollen and spores varied from 44 to 7,031×10−3 grains cm−2 yr−1 with maxima in oxygen isotope stages (OIS) 2, 3, 4, and around the OIS 4/5 boundary. Less rainfall during glacial times generally enhanced transport of pollen by wind to Site C4402. Their scavenging from the water column was promoted by high activity of the biological pump. Pollen record from core C4402 suggests that lower montane group vegetation was dominant relative to lowland vegetation and upper and mid-montane group during glacial times. Although appreciable contribution by terrestrial OM is expected from high correlation of MAR between organic carbon (OC) and pollen and spores, fairly low COrganic/N ratios and δ13C values (around −20‰) of OM demonstrate that OM in core C4402 is mainly of marine origin.

The Western Equatorial Pacific Ocean Circulation Study

Nature ◽  
1987 ◽  
Vol 330 (6148) ◽  
pp. 533-537 ◽  
Author(s):  
Eric Lindstrom ◽  
Roger Lukas ◽  
Rana Fine ◽  
Eric Firing ◽  
Stuart Godfrey ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Ocean Circulation ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Western Equatorial Pacific

The ‘sliced-cylinder’ laboratory model of the wind-driven ocean circulation. Part 1. Steady forcing and topographic Rossby wave instability

1975 ◽  
Vol 69 (1) ◽  
pp. 27-40 ◽  
Author(s):  
R. C. Beardsley ◽  
K. Robbins
Keyword(s):  
Boundary Layer ◽  
Ocean Circulation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Western Boundary Current ◽  
Boundary Layer Transition ◽  
Laboratory Model ◽  
Western Boundary ◽  
Boundary Current ◽  
Topographic Rossby Waves

The nonlinear response of the ‘sliced-cylinder’ laboratory model for the wind-driven ocean circulation is re-examined here in part 1 for the case of strong steady forcing. Introduced by Pedlosky & Greenspan (1967), the model consists of a rapidly rotating right cylinder with a planar sloping bottom. The homogeneous contained fluid is driven by the slow rotation of the flat upper lid relative to the rest of the basin. Except in thin Ekman and Stewartson boundary layers on the solid surfaces of the basin, the horizontal flow in the interior and western boundary layer is constrained by the rapid rotation of the basin to be independent of depth. The model thus effectively simulates geophysical flows through the physical analogy between topographic vortex stretching in the laboratory model and the creation of relative vorticity in planetary flows by the β effect.As the forcing is increased, the flow in both the sliced-cylinder laboratory and numerical models first exhibits downstream intensification in the western boundary layer. At greater forcing, separation of the western boundary current occurs with the development of stationary topographic Rossby waves in the western boundary-layer transition regions. The observed flow ultimately becomes unstable when a critical Ekman-layer Reynolds number is exceeded. We first review and compare the experimental and numerical descriptions of this low-frequency instability, then present a simple theoretical model which successfully explains this observed instability in terms of thelocalbreakdown of the finite-amplitude topographic Rossby waves embedded in the western boundary current transition region. The inviscid stability analysis of Lorenz (1972) is extended to include viscous effects, with the consequence that dissipative processes in the sliced-cylinder problem (i.e. lateral and bottom friction) are shown to inhibit the onset of the instability until the topographic Rossby wave slope exceeds a finite critical value.

Observations of the Mindanao Current during the western equatorial Pacific Ocean circulation study

1991 ◽  
Vol 96 (C4) ◽  
pp. 7089 ◽  
Author(s):  
Roger Lukas ◽  
Eric Firing ◽  
Peter Hacker ◽  
Philip L. Richardson ◽  
Curtis A. Collins ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Ocean Circulation ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Western Equatorial Pacific ◽  
Mindanao Current
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