Synoptic fluctuation of the Taiwan Warm Current in winter on the East China Sea shelf

Abstract. The seasonal mean and synoptic fluctuation of the wintertime Taiwan Warm Current (TWC) were investigated using a well validated finite volume community ocean model. The spatial distribution and dynamics of the synoptic fluctuation were highlighted. The seasonal mean of the wintertime TWC has two branches: an inshore branch between the 30 and 100 m isobaths and an offshore branch between the 100 and 200 m isobaths. The Coriolis term is much larger than the inertia term and is almost balanced by the pressure gradient term in both branches, indicating the geostrophic balance of the mean current. Two areas with significant fluctuations of the TWC were identified during wintertime. One of the areas is located to the north of Taiwan with velocities varying in the cross-shore direction. These significant cross-shore fluctuations are driven by barotropic pressure gradients associated with the intrusion of the Taiwan Strait Current (TSC). When a larger TSC intrudes north of Taiwan, the isobaric slope tilts downward from south to north, leading to a cross-shore current from the coastal area to the offshore area. When the TSC intrusion is weak, the cross-shore current to the north of Taiwan is directed from offshore to inshore. The other area of significant fluctuation is located in the inshore area, extending in the region between the 30 and 100 m isobaths. The fluctuations are generally strong in the alongshore direction, in particular at the latitudes 26.5° N and 28° N where they are important for the local cross-shore transports. Wind affects the synoptic fluctuation through episodic events. When the northeasterly monsoon prevails, the southward Zhe-Min Coastal Current dominates the inshore area associated with a deepening of the mixed layer. When the winter monsoon is weakened or the southerly wind prevails, the northward TWC dominates in the inshore area.

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Synoptic fluctuation of the Taiwan Warm Current in winter on the East China Sea shelf

Ocean Science ◽

10.5194/os-13-105-2017 ◽

2017 ◽

Vol 13 (1) ◽

pp. 105-122 ◽

Cited By ~ 8

Author(s):

Jiliang Xuan ◽

Daji Huang ◽

Thomas Pohlmann ◽

Jian Su ◽

Bernhard Mayer ◽

...

Keyword(s):

Ocean Model ◽

Coastal Current ◽

Gradient Term ◽

Taiwan Warm Current ◽

Offshore Area ◽

Warm Current ◽

Geostrophic Balance ◽

The North ◽

The Cross ◽

The Taiwan Strait

Abstract. The seasonal mean and synoptic fluctuation of the wintertime Taiwan Warm Current (TWC) were investigated using a well-validated finite volume community ocean model. The spatial distribution and dynamics of the synoptic fluctuation were highlighted. The seasonal mean of the wintertime TWC has two branches: an inshore branch between the 30 and 100 m isobaths and an offshore branch between the 100 and 200 m isobaths. The Coriolis term is much larger than the inertia term and is almost balanced by the pressure gradient term in both branches, indicating geostrophic balance of the mean current. Two areas with significant fluctuations of the TWC were identified during wintertime. One of the areas is located to the north of Taiwan with velocities varying in the cross-shore direction. These significant cross-shore fluctuations are driven by barotropic pressure gradients associated with the intrusion of the Taiwan Strait Current (TSC). When a strong TSC intrudes to the north of Taiwan, the isobaric slope tilts downward from south to north, leading to a cross-shore current from the coastal area to the offshore area. When the TSC intrusion is weak, the cross-shore current to the north of Taiwan is directed from offshore to inshore. The other area of significant fluctuation is located in the inshore area between the 30 and 100 m isobaths. The fluctuations are generally strong both in the alongshore and cross-shore directions, in particular at the latitudes 26.5 and 28° N. Wind affects the synoptic fluctuation through episodic events. When the northeasterly monsoon prevails, the southwestward Zhe-Min coastal current dominates the inshore area associated with a deepening of the mixed layer. When the winter monsoon is weakened or the southwesterly wind prevails, the northeastward TWC dominates in the inshore area.

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Generation of Upwelling Circulation under Downwelling-Favorable Wind within Bottom-Attached, Buoyant Coastal Currents

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0271.1 ◽

2017 ◽

Vol 47 (10) ◽

pp. 2499-2519 ◽

Cited By ~ 6

Author(s):

Sih-Yu Chen ◽

Shih-Nan Chen

Keyword(s):

Water Column ◽

Analytical Model ◽

Relative Size ◽

Ocean Model ◽

Velocity Shear ◽

Three Dimensions ◽

Coastal Current ◽

Driving Mechanism ◽

Geostrophic Balance ◽

The Cross

AbstractA two-dimensional modeling study by Moffat and Lentz recently reported that downwelling-favorable wind can induce cross-shore upwelling circulation within a bottom-attached, buoyant coastal current. Here, we extend the problem to three dimensions. The driving mechanism and the sensitivity for the upwelling circulation are studied, using a primitive equation ocean model and an analytical model. After the initial downwelling adjustment that steepens the isopycnals and compresses the coastal current, the cross-shore flow can switch to steady upwelling circulation. This reverse circulation coincides with a vertically well-mixed water column and persists until interrupted by the arrival of river plume bulge from upstream. During the upwelling phase, the ageostrophic cross-shore flow follows the Ekman balance. The sense of cross-shore circulation is governed by a dimensionless parameter, the shear ratio, which measures the relative size of geostrophic shear and velocity shear supported by the wind in the shallow-water limit. Upwelling circulation occurs when the shear ratio is greater than one. This condition represents that, near the surface, the wind-intensified pressure gradient exceeds the maximum possible Coriolis force associated with the wind-forced, alongshore flow. The resulting upwelling circulation acts to slump the isopycnals to restore the geostrophic balance. Therefore, within a coastal current, decreasing wind stress in fact strengthens the upwelling circulation, as a weaker wind produces a weaker shear and thus increases the imbalance. This inverse relation holds until the wind is too weak to mix the water column. Based on the analytical model, a regime classification for the cross-shore circulation under downwelling-favorable wind is proposed. An observational example is given.

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The observed variations of the north intrusion of the bottom Taiwan Warm Current Inshore Branch and its response to wind

Regional Studies in Marine Science ◽

10.1016/j.rsma.2019.100690 ◽

2019 ◽

Vol 30 ◽

pp. 100690 ◽

Cited By ~ 1

Author(s):

Jianfeng Wang ◽

Fei Yu ◽

Qiang Ren ◽

Guangcheng Si ◽

Chuanjie Wei

Keyword(s):

Taiwan Warm Current ◽

Warm Current ◽

The North

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The circulation of Icelandic waters – a modelling study

Ocean Science ◽

10.5194/os-9-931-2013 ◽

2013 ◽

Vol 9 (5) ◽

pp. 931-955 ◽

Cited By ~ 32

Author(s):

K. Logemann ◽

J. Ólafsson ◽

Á. Snorrason ◽

H. Valdimarsson ◽

G. Marteinsdóttir

Keyword(s):

Three Dimensional ◽

Atlantic Water ◽

Volume Transport ◽

Ocean Model ◽

The Arctic ◽

Coastal Current ◽

Mean Flow ◽

Model Code ◽

The North ◽

Icelandic Waters

Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic, including the Arctic Ocean, covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The simulation reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC) and the path of the Atlantic Water south-east of Iceland. The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts, which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a hitherto unnamed current over the southern and south-eastern shelf, which is simulated to be an upstream precursor of the Faroe Current (FC). Both currents are driven by barotropic pressure gradients induced by a sea level slope across the Greenland–Scotland Ridge. The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85% during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27%. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.

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The circulation of Icelandic waters – a modelling study

Ocean Science Discussions ◽

10.5194/osd-10-763-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 763-824 ◽

Cited By ~ 2

Author(s):

K. Logemann ◽

J. Ólafsson ◽

Á. Snorrason ◽

H. Valdimarsson ◽

G. Marteinsdóttir

Keyword(s):

Pressure Field ◽

Three Dimensional ◽

Atlantic Water ◽

Ocean Model ◽

The Arctic ◽

Coastal Current ◽

Mean Flow ◽

The South ◽

The North ◽

Icelandic Waters

Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic including the Arctic Ocean covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The model reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC), the path of the Atlantic Water south-east of Iceland and the structure of the North Icelandic Jet (NIJ). The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a current over the southern and south-eastern shelf herein called the South Icelandic Current (SIC). Both currents are driven by topographically induced distortions of the Arctic Front's barotropic pressure field. The SIC is simulated to be an upstream precursor of the Faroe Current (FC). The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85% during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27%. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.

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Response to a Steady Poleward Outflow. Part I: The Linear, Quasigeostrophic Problem

Journal of Physical Oceanography ◽

10.1175/2008jpo3999.1 ◽

2009 ◽

Vol 39 (7) ◽

pp. 1541-1550 ◽

Cited By ~ 1

Author(s):

Theodore S. Durland ◽

Joseph Pedlosky ◽

Michael A. Spall

Keyword(s):

Group Velocity ◽

Rossby Wave ◽

Spectral Element ◽

Coastal Current ◽

Wave Group ◽

Wave Speeds ◽

Geostrophic Balance ◽

The Cross ◽

Outflow Channel

Abstract The response of a zonal channel to a uniform, switched-on but subsequently steady poleward outflow is presented. An eastward coastal current with a Kelvin wave’s cross-shore structure is found to be generated instantly upon initiation of the outflow. The current is essentially in geostrophic balance everywhere except for the vicinity of the outflow channel mouth, where the streamlines must cross planetary vorticity contours to feed the current. The adjustment of this region generates a plume that propagates westward at Rossby wave speeds. The cross-shore structure of the plume varies with longitude, and at any given longitude it evolves with time. The authors show that the plume evolution can be understood both conceptually and quantitatively as the westward propagation of the Kelvin current’s meridional spectrum, with each spectral element propagating at its own Rossby wave group velocity.

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Does the Taiwan Warm Current originate in the Taiwan Strait in wintertime?

Journal of Geophysical Research Atmospheres ◽

10.1029/2005jc003281 ◽

2006 ◽

Vol 111 (C4) ◽

Cited By ~ 43

Author(s):

Chen-Tung Arthur Chen ◽

David D. Sheu

Keyword(s):

Taiwan Strait ◽

Taiwan Warm Current ◽

Warm Current ◽

The Taiwan Strait

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Thinner Sea Ice Contribution to the Remarkable Polynya Formation North of Greenland in August 2018

Advances in Atmospheric Sciences ◽

10.1007/s00376-021-0136-9 ◽

2021 ◽

Author(s):

Xiaoyi Shen ◽

Chang-Qing Ke ◽

Bin Cheng ◽

Wentao Xia ◽

Mengmeng Li ◽

...

Keyword(s):

Sea Ice ◽

Ice Cover ◽

Reanalysis Data ◽

Mean Value ◽

Ocean Model ◽

North Coast ◽

Average Value ◽

The North ◽

Wind Sea ◽

The One

AbstractIn August 2018, a remarkable polynya was observed off the north coast of Greenland, a perennial ice zone where thick sea ice cover persists. In order to investigate the formation process of this polynya, satellite observations, a coupled ice-ocean model, ocean profiling data, and atmosphere reanalysis data were applied. We found that the thinnest sea ice cover in August since 1978 (mean value of 1.1 m, compared to the average value of 2.8 m during 1978–2017) and the modest southerly wind caused by a positive North Atlantic Oscillation (mean value of 0.82, compared to the climatological value of −0.02) were responsible for the formation and maintenance of this polynya. The opening mechanism of this polynya differs from the one formed in February 2018 in the same area caused by persistent anomalously high wind. Sea ice drift patterns have become more responsive to the atmospheric forcing due to thinning of sea ice cover in this region.

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