Identification and census statistics of multicore eddies based on sea surface height data in global oceans
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Identification and census statistics of multicore eddies based on sea surface height data in global oceans Wei Cui1, 2, Wei Wang2, Jie Zhang1, Jungang Yang1* 1 First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China 2 Physical Oceanography Lab, Qingdao Collaborative Innovation Center of Marine Science and Technology, Ocean
University of China, Qingdao 266100, China Received 28 July 2018; accepted 5 November 2018 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
This study produced a statistical analysis of multicore eddy structures based on 23 years' altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority (70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents. Key words: satellite altimetry, mesoscale eddy, multicore structure, eddy identification, eddy characteristic Citation: Cui Wei, Wang Wei, Zhang Jie, Yang Jungang. 2020. Identification and census statistics of multicore eddies based on sea surface height data in global oceans. Acta Oceanologica Sinica, 39(1): 41–51, doi: 10.1007/s13131-019-1519-y
1 Introduction The term “mesoscale eddy” applied to a rotating coherent structure of ocean currents that resembles an atmospheric storm, generally refers to ocean signals with spatial scales from tens to hundreds of kilometers and temporal scales from days to months (Robinson, 2010). Eddies can be found nearly everywhere in the world ocean (Abernathey and Marshall, 2013; Chelton et al., 2011b), and they transport water, heat, salt, and energy as they propagate in the ocean (Dong et al., 2014; Roemmich and Gilson, 2001; Thompson et al., 2014; Xu et al., 2011). Eddies also play a significant role in transferring soluble carbon, chlorophyll, nutrients, and other tracers across the ocean, and have important influences on the marine ecosystem (Adam
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