Seasonality of the Mindanao Current/Undercurrent System

Ren, Qiuping; Li, Yuanlong; Wang, Fan; Song, Lina; Liu, Chuanyu; Zhai, Fangguo

doi:10.1002/2017jc013474

Cited by 34 publications

(39 citation statements)

References 58 publications

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“…All the currents and undercurrents generated by our model have reasonable widths, depths and intensities as compared to previous studies (Qu et al 1998;Wang et al 2015). The vertical structures of the upper currents/undercurrents are consistent with the ADCP mooring observations Ren et al 2018;Zhang et al 2014Zhang et al , 2017. The northward weakening and deepening of the NEUC jets are clearly revealed (Fig.…”

Section: A General Flow Patternsupporting

confidence: 88%

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On the Formation Dynamics of the North Equatorial Undercurrent

Gan

2020

Journal of Physical Oceanography

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Based on a physics-oriented modeling study, we investigate the underlying forcing processes of the North Equatorial Undercurrent (NEUC). Made up of large-scale (~90%) and mesoscale (~10%) components, the NEUC weakens eastward with a longitude-independent seasonality. The large-scale component reflects the effect of the meridional baroclinic pressure gradient force (PGF_BC). The vertical velocity shear forms the eastward NEUC, when the PGF_BC exceeds the meridional barotropic pressure gradient force (PGF_BT). The mesoscale variability with alternating jets is linked to the wind stress curl in different regions of the tropical North Pacific. Spatially, the NEUC has a northern (NEUC_N) and a southern branch (NEUC_S), which are mainly attributed to the transports from Luzon Undercurrent (LUC) and Mindanao Undercurrent (MUC), respectively. The LUC of ~3 Sv (1 Sv ≡ 106 m3 s−1) feeds the NEUC_N in summer, while the MUC of ~4 Sv fuels the NEUC_S in autumn and the two branches do not coexist. The total NEUC transport peaks in August/September, and there exist three distinct periods in a 1-yr cycle: the non-NEUC period in winter, the LUC-driven period in summer, and the MUC-driven period in autumn. Based on the layer-integrated vorticity equation, we diagnose quantitatively that the variation of the NEUC is dominated by the lateral planetary vorticity influx from the LUC and the MUC. These external influxes interact with the internal dynamics of pressure torques and stress curls in the NEUC layer, to jointly govern the NEUC and its variability. Meanwhile, the nonlinearity due to relative vorticity advection near the coast modulates the strength of the NEUC.

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Section: A General Flow Patternsupporting

confidence: 88%

“…12a). By utilizing one-point mooring observation, Ren et al (2018) showed that the MUC has a semiannual variation peaking in summer and winter. We also find similar seasonal phase of the MUC at a single longitude near the coast (not shown here).…”

Section: Dynamic Linkage Among the Undercurrentsmentioning

confidence: 99%

On the Formation Dynamics of the North Equatorial Undercurrent

Gan

2020

Journal of Physical Oceanography

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“…Dynamics of the MC/MUC variability are intriguing owing to the complicated relationship between the two currents. Historical observations and numerical models have been utilized to understand the MC's variabilities on time scales ranging from intraseasonal to decadal (e.g., Lukas 1988;Qiu and Lukas 1996;Tozuka et al 2002;Kashino et al 2005Kashino et al , 2009Kashino et al , 2011Qu et al 2012;Zhao et al 2012;Zhang et al 2014;Wang et al 2016b;Hu et al 2016;Ren et al 2018;Duan et al 2019a,b). On interannual time scale, it has been well established that El Niño-Southern Oscillation (ENSO) is the dominant climate mode of the tropical Pacific and plays the major role in driving variability of the western Pacific circulation (e.g., Qiu and Lukas 1996;Kim et al 2004;Kashino et al 2005Kashino et al , 2009Kashino et al , 2011.…”

Section: Introductionmentioning

confidence: 99%

“…In comparison, our knowledge of the MUC's interannual variability is much more fragmental due to a lack of continuous subthermocline observation. While existing research has revealed evident intraseasonal and seasonal variabilities of the MUC (Kashino et al 2011;Zhang et al 2014;Wang et al 2014Wang et al , 2016aRen et al 2018), few studies address interannual variability of the MUC. By analyzing mooring data, Hu et al (2016) documented weak interannual fluctuations of the MUC with a typical period shorter than that of the MC.…”

Section: Introductionmentioning

confidence: 99%

Variability of the Mindanao Current Induced by El Niño Events

Ren

Wang

et al. 2020

Journal of Physical Oceanography

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Historical observations have documented prominent changes of the Mindanao Current (MC) during El Niño events, yet a systematic understanding of how El Niño modulates the MC is still lacking. Mooring observations during December 2010–August 2014 revealed evident year-to-year variations of the MC in the upper 400 m that were well reproduced by the Hybrid Coordinate Ocean Model (HYCOM). Composite analysis was conducted for 10 El Niño events during 1980–2015 using five model-based datasets (HYCOM, OFES, GEOS-ODA, SODA2.2.4, and SODA3.3.1). A consensus is reached in suggesting that a developing (decaying) El Niño strengthens (weakens) the MC, albeit with quantitative differences among events and datasets. HYCOM experiments demonstrate that the MC variability is mainly a first baroclinic mode response to surface wind forcing of the tropical Pacific, but the specific mechanism varies with latitude. The upstream part of the MC north of 7.5°N is controlled by wind forcing between 6° and 9°N through Ekman pumping, whereas its downstream part south of 7.5°N is greatly affected by equatorial winds. Prevailing westerly winds and Ekman upwelling in the developing stage cause cyclonic anomalous circulation in the northwest tropical Pacific that strengthens the MC, and the opposite surface wind forcing effect in the decaying stage weakens the MC. Although ocean models show difficulties in realistically representing the northward-flowing Mindanao Undercurrent (MUC) beneath the MC and its seasonal and interannual variations, all five products suggest an enhancement of the MUC during the decaying stage of El Niño.

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“…The MC also exhibits strong seasonal and interannual variations in response to tropical Pacific wind forcing, as revealed by in situ observations, model simulations, and ocean reanalysis products (e.g., Kashino et al, , ; Qiu & Lukas, ; Qu et al, ; Schönau et al, ; Wang & Hu, ). The MC achieves its maximum strength in boreal spring and minimum strength in boreal fall (e.g., Chen & Wu, ; Kashino et al, ; Qiu & Lukas, ; Qu & Lukas, ; Qu et al, ; Ren et al, ; Yaremchuk & Qu, ). Interannual variations of the MC were shown to be related with El Niño–Southern Oscillation (ENSO) (Hu et al, ; Kashino et al, ; Kim et al, ), although Lukas () found no evident relationship between the sea level in the MC region and ENSO.…”

Section: Introductionmentioning

confidence: 99%

Decadal Variations of the Mindanao Current During 1960–2010

Duan

Wang

et al. 2019

JGR Oceans

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Results from an eddy‐resolving ocean model simulation, an ocean reanalysis data, and reduced‐gravity ocean (RGO) model simulations reach consensus in suggesting prominent decadal fluctuations of the Mindanao Current (MC) during 1960–2010. The MC was evidently enhanced during 1974–1982 and 2002–2008 and weakened during 1983–1990 and 1994–2001, with typical amplitude of ~2.0 Sv (1 Sv ≡ 106 m3/s) for decadal volume transport anomaly. These variations are closely associated with the strength of the westward flowing North Equatorial Current at 130°E and not evidently related with its bifurcation latitude. Experiments using a 1.5‐layer RGO model are performed to understand the mechanisms. Decadal variations of the MC are primarily caused by off‐equatorial wind changes in the tropical North Pacific, and winds in the latitude range of the MC (3–13°N) play the dominant role. Equatorial winds between 3°S and 3°N generally act to attenuate the MC variability, and subtropical winds have little contribution. For zonal distribution, local wind forcing between 120 and 160°E explains 67.8% of the MC decadal variability, while those in the central and eastern Pacific have weaker effects (25.0% and 7.2%, respectively). RGO model runs forced by nine wind data sets confirm the tight relationship between the MC and the western Pacific winds since the 1980s. The anomalous westerly winds under El Niño‐like condition drive upwelling in the Philippine Sea through off‐equatorial Ekman pumping that strengthens the MC. The relationship prior to 1980 is sensitive to the choice of wind data set, with four data sets yielding low or negative correlations.

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Seasonality of the Mindanao Current/Undercurrent System

Cited by 34 publications

References 58 publications

On the Formation Dynamics of the North Equatorial Undercurrent

On the Formation Dynamics of the North Equatorial Undercurrent

Variability of the Mindanao Current Induced by El Niño Events

Decadal Variations of the Mindanao Current During 1960–2010

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