Limits...
Observed deep energetic eddies by seamount wake.

Chen G, Wang D, Dong C, Zu T, Xue H, Shu Y, Chu X, Qi Y, Chen H - Sci Rep (2015)

Bottom Line: It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s).The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy.Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.

ABSTRACT
Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

No MeSH data available.


Long-term moored current record.(a) Time series of the mean 400–450 m (thin-red line), 1175–1225 m (thick-blue line) velocity amplitudes and the mean across-isobath velocity component at 1175–1225 m (thick-gray line; negative values mean northwestward) observed by mooring B from May 2009 to August 2012. (b) Spatial structure of the first two horizontal velocity modes. (c) The power spectrum of the mean across-isobath velocity component at 1175–1225 m and the 95% confidence curve (gray line). Figures are plotted using MATLAB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4663540&req=5

f6: Long-term moored current record.(a) Time series of the mean 400–450 m (thin-red line), 1175–1225 m (thick-blue line) velocity amplitudes and the mean across-isobath velocity component at 1175–1225 m (thick-gray line; negative values mean northwestward) observed by mooring B from May 2009 to August 2012. (b) Spatial structure of the first two horizontal velocity modes. (c) The power spectrum of the mean across-isobath velocity component at 1175–1225 m and the 95% confidence curve (gray line). Figures are plotted using MATLAB.

Mentions: The time evolution of 1175–1225 m depth-averaged velocities (blue line in Fig. 6a) suggests more than 72% of velocities are less than 0.04 m/s during May 2009 and August 2012. However, larger velocities, even larger than that at 400–450 m (red line in Fig. 6a), are also observed, for example, in June 2009, September 2009, August 2010, May 2012 and so on. These events last longer than 3 weeks and all of them correspond to strong northward currents at earlier time in the upper layer (Figure S2). Empirical orthogonal function analysis is applied to analyze the velocity observations by mooring B. The result shows that the first three dominant modes account for 68%, 16% and 6%, respectively, of the total variance. Mode 1 demonstrates the deep currents are mainly southwestward or northeastward (Fig. 6b), which should be attributed to the impact of the west boundary current in the SCS. Besides, the deep currents are nearly uniform as the no eddy situation in most of the time shown in Fig. 2f. Mode 2 represents the sheared deep currents, implying that some events affect the deep-sea conditions. The sheared currents tend to be across-isobath slanted in the northwest-southeast direction.


Observed deep energetic eddies by seamount wake.

Chen G, Wang D, Dong C, Zu T, Xue H, Shu Y, Chu X, Qi Y, Chen H - Sci Rep (2015)

Long-term moored current record.(a) Time series of the mean 400–450 m (thin-red line), 1175–1225 m (thick-blue line) velocity amplitudes and the mean across-isobath velocity component at 1175–1225 m (thick-gray line; negative values mean northwestward) observed by mooring B from May 2009 to August 2012. (b) Spatial structure of the first two horizontal velocity modes. (c) The power spectrum of the mean across-isobath velocity component at 1175–1225 m and the 95% confidence curve (gray line). Figures are plotted using MATLAB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663540&req=5

f6: Long-term moored current record.(a) Time series of the mean 400–450 m (thin-red line), 1175–1225 m (thick-blue line) velocity amplitudes and the mean across-isobath velocity component at 1175–1225 m (thick-gray line; negative values mean northwestward) observed by mooring B from May 2009 to August 2012. (b) Spatial structure of the first two horizontal velocity modes. (c) The power spectrum of the mean across-isobath velocity component at 1175–1225 m and the 95% confidence curve (gray line). Figures are plotted using MATLAB.
Mentions: The time evolution of 1175–1225 m depth-averaged velocities (blue line in Fig. 6a) suggests more than 72% of velocities are less than 0.04 m/s during May 2009 and August 2012. However, larger velocities, even larger than that at 400–450 m (red line in Fig. 6a), are also observed, for example, in June 2009, September 2009, August 2010, May 2012 and so on. These events last longer than 3 weeks and all of them correspond to strong northward currents at earlier time in the upper layer (Figure S2). Empirical orthogonal function analysis is applied to analyze the velocity observations by mooring B. The result shows that the first three dominant modes account for 68%, 16% and 6%, respectively, of the total variance. Mode 1 demonstrates the deep currents are mainly southwestward or northeastward (Fig. 6b), which should be attributed to the impact of the west boundary current in the SCS. Besides, the deep currents are nearly uniform as the no eddy situation in most of the time shown in Fig. 2f. Mode 2 represents the sheared deep currents, implying that some events affect the deep-sea conditions. The sheared currents tend to be across-isobath slanted in the northwest-southeast direction.

Bottom Line: It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s).The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy.Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.

ABSTRACT
Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

No MeSH data available.