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Frontiers of Earth Science

Front. Earth Sci.    2015, Vol. 9 Issue (2) : 202-208     DOI: 10.1007/s11707-014-0478-z
RESEARCH ARTICLE |
The most typical shape of oceanic mesoscale eddies from global satellite sea level observations
Zifei WANG1,Qiuyang LI1,Liang SUN1,2,*(),Song LI1,Yuanjian YANG1,3,Shanshan Liu1,2
1. Key Laboratory of the Atmospheric Composition and Optical Radiation, CAS, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
2. State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, HangZhou 310012, China
3. Key Laboratory of Atmospheric Sciences and Satellite Remote Sensing of Anhui Province, Anhui Institute of Meteorological Sciences, Hefei 230031, China
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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.

Keywords sea level anomaly      ocean eddies      Taylor vortex      typical shape     
Corresponding Authors: Liang SUN   
Online First Date: 17 December 2014    Issue Date: 30 April 2015
 Cite this article:   
Zifei WANG,Liang SUN,Song LI, et al. The most typical shape of oceanic mesoscale eddies from global satellite sea level observations[J]. Front. Earth Sci., 2015, 9(2): 202-208.
 URL:  
http://journal.hep.com.cn/fesci/EN/10.1007/s11707-014-0478-z
http://journal.hep.com.cn/fesci/EN/Y2015/V9/I2/202
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Zifei WANG
Liang SUN
Song LI
Yuanjian YANG
Shanshan Liu
Qiuyang LI
Fig.1  (a) A typical Gaussian eddy profile (squares) and fitting profile (curve) with A = ?35.1 cm, Le= 62.8 km, B = 7.4 cm and x0= ?19.1 km. (b) The profiles of the direct normalization (triangles) and the optimal normalization (circles) are shown, and the curve is the profile from the normalized Gaussian function.
Fig.2  (a) A typical Gaussian eddy profile with A = 21 cm, Le = 60.4 km, B = 1.8 cm and x0= 1.8 km. (b) Probability density function distribution of the normalized SLA shape for Gaussian eddies.
Fig.3  (a) A typical quadratic eddy with A = 61.8 cm, Le= 92.6 km, B = ?17.7 cm, and x0= 2.2 km; (b) Probability density function distribution of the normalized SLA shape for quadratic eddies.
Fig.4  The rest type of eddies. (a) A combination eddy consisting of two Gaussian eddies (left: A = 45 cm, Le = 132.2 km, B = ?10.3 cm and x0= 0.65 km; right: A = 18.5 cm, Le = 121.3 km, B = 16.46 cm and x0= 7.24 km). (b) Probability density function distribution of the normalized SLA shape of Gaussian eddies.
Fig.5  Numbers of eddies per map and ratios of the different types of eddies.
Fig.6  (a) Distribution of B and A of the eddies. (b) Mean and standard deviation of B vs. A. (c) The distribution of x0 and Le of the eddies. (d) Mean and standard deviation of x0 vs. Le.
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