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Dipole eddy detection from satellite and its dynamic modulation in the global ocean

  • role： First author第一作者
  • Affiliation：

    School of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

  • Email：yulele3200@163.com
  • Introduction：禹乐乐，研究方向为海洋遥感与海洋大数据分析。E-mail： yulele3200@163.com
YU Lele1,  
  • Affiliation：

    School of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

CAO Chuanchuan1,  
  • Affiliation：

    School of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

    School of Physics and Optoelectronics Engineering, Weifang University, Weifang 261061, China

WANG Xuan13,  
  • role： Corresponding author通信作者
  • Affiliation：

    School of Information Science and Engineering, Ocean University of China, Qingdao 266100, China

    Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China

  • Email：gechen@ouc.edu.cn
  • Introduction：陈戈，研究方向为海洋遥感与大数据海洋学。E-mail： gechen@ouc.edu.cn
CHEN Ge12*

Resümee

Eddies play an important role in water transport and energy balance in the ocean. Ocean observations show that eddies are not isolated, and cyclonic eddies and anti-cyclonic eddies always form more stable structures: dipole eddies. Dipole eddies have a more evident dynamic modulation compared with monopole eddies. Moreover, dipole eddies enhance the vertical movement of water to ensure that they promote the propagation and distribution of heat, energy, and organic matter in the ocean, which affects the global biochemical process. The parameters’ variations of dipole eddies during propagation must be examined to extensively understand the coupling state of eddies. The quantitative analysis of the modulation effect can provide a reference for exploring the dynamic mechanism of dipole eddies.In this work, the Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) merged data from a combination of T/P, Jason-1, Jason-2, Jason-3, and Envisat missions are used to identify and track eddies in the global ocean during 1993—2020. These data have a daily temporal resolution and a 1/4°×1/4° spatial resolution. We established criteria for extracting dipole eddies based on eddy identification and track data: the distance of eddy cores is less than twice the sum of their radii, and their concomitant time is more than 60 days. We analyze the variations of eddies’ parameters to reveal the role of the dipole in modulating eddies based on over 67,500 dipole eddies that we found.The results show that dipoles are distributed in 10°N—60°N and 11°S—66°S. The dipole eddies are composed of eddies at a probability of over 15% and in the strong currents region, the frequency of dipole eddies formation is higher, even more than 35%. Given that the dipole structure influences the movement and propagation of eddies, we demonstrate it by using four dominating parameters of eddies, including amplitude, radius, EKE, and vorticity. Result showed that the dipole structures increase the amplitude by 5%—14%, radius by 2%—9%, and EKE by 4%—13% but suppress the vorticity of eddies by less than 3%. Furthermore, the various ratios of the parameters reach the peak at the middle of eddy normalized life. The dipole structures also promote the geostrophic and propagation velocities. The geostrophic velocity of eddies is significantly enhanced in strong current areas. In addition, the enhancement of geostrophic velocity of eddy is zonally distributed and gradually decreases from the equator to the poles.We conclude that dipole structures change the initial state of the eddies, causing some parameter variations: amplitude, radius, and EKE of eddies are increased by less than 13%, while vorticity is reduced. The dipole structures also have a certain acceleration effect on eddies at propagation and geostrophic velocities. Futhermore, the coupling of eddies with opposite polarity enhances their fluctuation and causes them to interact. The dynamic mechanism and ecological effect of eddies coupling based on better data sets are also the focus of future work.

Schlüsselwort

remote sensing;satellite altimeter;mesoscale eddy;dipole eddy;parametric statistics;modulation effect

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