An irregularly shaped warm eddy observed by Chinese underwater gliders

Mesoscale eddies are important for transporting oceanic energy and matter. We investigated the three-dimensional structure of an irregularly shaped warm eddy using three Chinese underwater gliders and satellite data during May 2015 in the northern South China Sea. The warm eddy lasted for 2 months, remained quasi-steady, and had a mean radius of ~ 70 km from May 10 to May 31. The heat contents observed along the two glider tracks differed markedly, by 2 × 109 J/m2, which reflected an imbalance in the geostrophic and tangential velocity distributions of the eddy. The geostrophic/tangential velocity decreased/increased with depth within the warm eddy. The maximum tangential velocities calculated using the datasets from the two gliders were 0.8 and 0.25 m/s, respectively, confirming that the shape of the warm eddy was horizontally asymmetrical. Large errors can arise when the heat, energy, and matter transport for an irregularly shaped eddy are estimated using a regular circular model. We suggest that more intersecting glider tracks should be used to retrieve the three-dimensional eddy structure, and that those tracks should be better designed. The irregular shape of the warm eddy was likely induced by oceanic currents such as the wind-induced Ekman current. Further study is needed to elucidate the eddy–current interactions and the mechanisms thereof.

[1]  W. Zhuang,et al.  Evolution of an anticyclonic eddy southwest of Taiwan , 2013, Ocean Dynamics.

[2]  Huijie Xue,et al.  Oceanic eddy formation and propagation southwest of Taiwan , 2011 .

[3]  Ying Feng,et al.  Cruise Observation of Rossby Waves with Finite Wavelengths Propagating from the Pacific to the South China Sea , 2016 .

[4]  Quanan Zheng,et al.  Penetration of nonlinear Rossby eddies into South China Sea evidenced by cruise data , 2012 .

[5]  Frits H. Post,et al.  Detection, quantification, and tracking of vortices using streamline geometry , 2000, Comput. Graph..

[6]  Huijie Xue,et al.  Glider-observed anticyclonic eddy in northern South China Sea , 2016 .

[7]  Qinyu Liu,et al.  Eddy Shedding from the Kuroshio Bend at Luzon Strait , 2004 .

[8]  Jianyu Hu,et al.  Progress on upwelling studies in the China seas , 2016 .

[9]  Jorge Tam,et al.  Average circulation, seasonal cycle, and mesoscale dynamics of the Peru Current System: A modeling approach , 2005 .

[10]  Huasheng Hong,et al.  A Review on the Currents in the South China Sea: Seasonal Circulation, South China Sea Warm Current and Kuroshio Intrusion , 2000 .

[11]  Yu Tian,et al.  Motion Parameter Optimization and Sensor Scheduling for the Sea-Wing Underwater Glider , 2013, IEEE Journal of Oceanic Engineering.

[12]  Huijie Xue,et al.  An exceptional anticyclonic eddy in the South China Sea in 2010 , 2014 .

[13]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[14]  Lei Zhou,et al.  The Roles of Kuroshio Intrusion and Mesoscale Eddy in Upper Mixing in the Northern South China Sea , 2013 .

[15]  W. Timothy Liu,et al.  Summer upwelling in the South China Sea and its role in regional climate variations , 2003 .

[16]  H. Mitsudera,et al.  On the eddy-Kuroshio interaction: Evolution of the mesoscale eddy , 2002 .

[17]  Q. Xie,et al.  Sea surface cooling in the Northern South China Sea observed using Chinese sea-wing underwater glider measurements , 2015 .

[18]  Wei Zhao,et al.  Observed 3D Structure, Generation, and Dissipation of Oceanic Mesoscale Eddies in the South China Sea , 2016, Scientific Reports.

[19]  Su Jilan,et al.  Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary , 2004 .

[20]  Daniel L. Rudnick,et al.  Cyclonic Eddies in the Gulf of Mexico: Observations by Underwater Gliders and Simulations by Numerical Model , 2015 .

[21]  B. Qiu,et al.  Oceanic mass transport by mesoscale eddies , 2014, Science.

[22]  G. I. Bell.  Interaction between vortices and waves in a simple model of geophysical flow , 1990 .

[23]  Li Li,et al.  Anticyclonic rings from the Kuroshio in the South China Sea , 1998 .

[24]  Charles C. Eriksen,et al.  Buoyant Eddies Entering the Labrador Sea Observed with Gliders and Altimetry , 2007 .

[25]  D. Chelton,et al.  Global observations of nonlinear mesoscale eddies , 2011 .

[26]  P. Xiu,et al.  Modeled biogeochemical responses to mesoscale eddies in the South China Sea , 2011 .

[27]  Feng-Chun Su,et al.  Satellite altimeter observations of nonlinear Rossby eddy–Kuroshio interaction at the Luzon Strait , 2011 .

[28]  Ananda Pascual,et al.  Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry , 2016 .

[29]  Feng Nan,et al.  Three long‐lived anticyclonic eddies in the northern South China Sea , 2011 .

[30]  D. Griffin,et al.  The effect of surface flooding on the physical-biogeochemical dynamics of a warm-core eddy off southeast Australia , 2011 .

[31]  G. Shutts.  The propagation of eddies in diffluent jetstreams: Eddy vorticity forcing of ‘blocking’ flow fields , 1983 .

[32]  Huijie Xue,et al.  Kuroshio intrusion into the South China Sea: A review , 2015 .

[33]  Gengxin Chen,et al.  Eddy heat and salt transports in the South China Sea and their seasonal modulations , 2012 .

[34]  J. McWilliams,et al.  A Formal Theory for Vortex Rossby Waves and Vortex Evolution , 2003 .

[35]  Dongliang Yuan,et al.  Surface Kuroshio path in the Luzon Strait area derived from satellite remote sensing data , 2006 .

[36]  W. Timothy Liu,et al.  Spacebased observations of the seasonal changes of south Asian monsoons and oceanic responses , 1999 .

[37]  Rossby Waves and Eddies Observed at a Temperature Mooring in Northern South China Sea , 2016 .