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引用本文:

DOI:

10.11834/jrs.20221690

收稿日期:

2021-10-29

修改日期:

2022-04-16

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全球海洋偶极子涡旋特征提取与动力调制的遥感研究
禹乐乐, 曹川川, 王璇, 陈戈
中国海洋大学 信息科学与工程学部海洋技术学院
摘要:

中尺度涡旋具有封闭的环流结构,在海洋物质输运与能量平衡方面发挥了重要作用。观测表明海洋中涡旋并非是孤立的:气旋涡与反气旋涡倾向于相互伴随而形成稳定传播的偶极子结构。本文以1993年至2020年卫星高度计识别与追踪的中尺度涡旋数据为基础,结合涡旋的时空特征提出了偶极子涡旋的判据,建立偶极子涡旋数据集。结果表明偶极子涡旋主要分布于南北纬10°至70°纬度范围内,且平均占比约为29.53%。偶极子结构的形成对涡旋有明显的调制作用,相对于非偶极子状态,偶极子状态的涡旋振幅的增强幅度为11.09%、半径的增强幅度为7.33%、动能的增强幅度为8.58%,涡旋涡度的减小幅度为1.34%。同时,调制作用与涡旋所处的纬度和生命状态有关。在运动特征方面,偶极子状态下涡旋的传播稍有增速,变化在10%以内,而平均地转流速的最大增幅超过30%,其高值对应海洋的强流区。全球偶极子涡旋的定量分析将有助于深化对涡旋动力学的理解,为进一步剖析涡-涡相互作用机理与精细化海洋数值模拟奠定基础。

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

Eddies play an important role in water transport and energy balance in the ocean. Ocean observations show that eddies are not isolated, cyclonic eddies and anti-cyclonic eddies always form more stable structures: dipole eddies. Dipole eddies have more evident dynamic modulation compared to monopole eddies. Moreover, dipole eddies enhance the vertical movement of water so that they promote the propagation and distribution of heat, energy, and organic matter in the ocean, which affects the global biochemical process. To understand the coupling state of eddies better, the parameters’ variations of dipole eddies during propagation need to be examined. The quantitative analysis of the modulation effect can provide a reference for exploring the dynamic mechanism of dipole eddies. In this paper,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. It has a daily temporal resolution and a 1/4°× 1/4° spatial resolution. We proposed criteria to extract 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 total concomitant time is more than 60 days. Based on over 67500 dipole eddies that we have found, we analyze the variations of eddies’ parameters to reveal the role of the dipole in modulating eddies. The results show that dipoles are distributed in 10°N ~ 60°N and 11°S ~ 66°S . In general, 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%. The dipole structure influences the movement and propagation of eddies, we demonstrate it by four dominating parameters of eddies, including amplitude, radius, EKE and vorticity. We find that the dipole structures increase the amplitude by 5~14%, radius by 2~9% and EKE by 4~13% while the dipole structures suppress the vorticity of eddies by less than 3%. What’s more, the various ratios of the parameters reach the peak at the middle of eddy normalized life. The dipole structures also promote the geostrophic velocity and propagation velocity. The geostrophic velocity of eddies is enhanced significantly in strong currents areas. In addition, the enhancement of geostrophic velocity of eddy is zonally distributed and decreases gradually 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 velocity and geostrophic velocity. It can be seen that the coupling of eddies with opposite polarity enhances the fluctuation of eddies and makes them interact with each other. The dynamic mechanism and ecological effect of eddies coupling based on better data sets are also the focus of future work.

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