The most typical shape of oceanic mesoscale eddies from global satellite sea level observations

Abstract

In this research, we normalized the characteristics of ocean eddies by using satellite observation of the Sea Level Anomaly (SLA) data to determine the most typical shape of ocean eddies. This normalization is based on modified analytic functions with nonlinear optimal fitting. The most typical eddy is the Taylor vortex (~50%), which exhibits a Gaussian-shaped exp(-r²) SLA and a vorticity distribution of (1-r²)exp(-r²) as a function of the normalized radii r. The larger the amplitude of the eddy, the more likely the eddy is to be Gaussian-shaped. Furthermore, approximately 40% of ocean eddies are combinations of two Gaussian eddies with different parameters, but the composition of these types of eddies is more like a quadratic eddy than a Gaussian one. Only a small portion of oceanic eddies are pure quadratic eddies (<10%) with the same vorticity distribution as a Rankine vortex. We concluded that the Taylor vortex is a good approximation of the typical shape of ocean eddies.

Key words： sea level anomaly; ocean eddies; Taylor vortex; typical shape

Acknowledgements

We thank the three anonymous reviewers for their constructive suggestions. This work was supported by the National Basic Research Program of China (Nos. 2012CB417402 and 2013CB430303) and the National Natural Science Foundation of China (Grant Nos. 41376017 and 41205126) and the Open Research Fund of Key Laboratory of Atmospheric Composition and Optical Radiation of Chinese Academy of Sciences (Grant No. JJ1102). We thank AVISO for providing the SLA data and the open fund of State Key Laboratory of Satellite Ocean Environment Dynamics (No. SOED1501).

References

1 Chaigneau A, Gizolme A, Grados C (2008). Mesoscale eddies off Peru in altimeter records: identification algorithms and eddy spatio-temporal patterns. Prog Oceanogr, 79(2-4): 106-119

2 Chaigneau A, Le Texier M, Eldin G, Grados C, Pizarro O (2011). Vertical structure of mesoscale eddies in the eastern South Pacific Ocean: A composite analysis from altimetry and Argo profiling floats. Journal of Geophysical Research: Oceans, 116(C11): C11025

3 Chelton D B, Gaube P, Schlax M G, Early J J, Samelson R M (2011b). The influence of nonlinear mesoscale eddies on near surface oceanic Chlorophyll. Science, 334(6054): 328-332

4 Chelton D B, Schlax M G, Samelson R M (2011a). Global observations of nonlinear mesoscale eddies. Prog Oceanogr, 91(2): 167-216

5 Chelton D B, Schlax M G, Samelson R M, de Szoeke R A (2007). Global observations of large oceanic eddies. Geophys Res Lett, 34(15): L15606

6 Dong C, Lin X, Liu Y, Nencioli F, Chao Y, Guan Y, Chen D, Dickey T, McWilliams J C (2012). Three-dimensional oceanic eddy analysis in the Southern California Bight from a numerical product. J Geophys Res, 117: C00H14

7 Dong C, McWilliams J C, Liu Y, Chen D (2014). Global heat and salt transports by eddy movement. Nature Communications, 5: 3294

8 Ducet N, Le Traon P Y, Reverdin G (2000), Global high resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2, J. Geophys. Res., 105, 19,477-19,478

9 Early J J, Samelson R M, Chelton D B (2011). The evolution and propagation of quasigeostrophic ocean eddies. J Phys Oceanogr, 41(8): 1535-1555

10 Hu J, Gan J, Sun Z, Zhu J, Dai M (2011). Observed three-dimensional structure of a cold eddy in the southwestern South China Sea. J Phys Oceanogr, 116: C05016

11 Isern-Fontanet J, Garcia-Ladona E, Font J (2003). Identification of marine eddies from altimetric maps. J Atmos Ocean Technol, 20(5): 772-778

12 Li Q Y, Sun L, Liu S S, Xian T, Yan Y F (2014). A new mononuclear eddy identification method with simple splitting strategies. Remote Sensing Letters, 5 (1): 65-72

13 Ponte R M, Wunsch C, Stammer D (2007). Spatial Mapping of Time-Variable Errors in Jason-1 and TOPEX/Poseidon Sea Surface Height Measurements. J Atmos Ocean Technol, 24(6): 1078-1085

14 Roemmich D, Gilson J (2001). Eddy transport of heat and thermocline waters in the North Pacific: a key to interannual/decadal climate variability? J Phys Oceanogr, 31(3): 675-687

15 Sun L (2011). A typhoon-like vortex solution of incompressible 3D inviscid flow. Theor Appl Mech Lett, 1(4): 042003

16 Wu J Z, Ma H Y, Zhou M D (2006). Vorticity and Vortex Dynamics. Berlin-Heidelberg: Springer-Verlag. XIV, 776 p., 291 illus

17 Yang G, Wang F, Li Y, Lin P (2013). Mesoscale eddies in the northwestern subtropical Pacific Ocean: Statistical characteristics and three‐dimensional structures. Journal of Geophysical Research: Oceans, 118(4): 1906-1923

18 Zhang Z G, Zhang Y, Wang W, Huang R X (2013). Universal structure of mesoscale eddies in the ocean. Geophys Res Lett, 40(14): 3677-3681