Abstract
Abstract. This study investigated the statistics of eddy splitting and merging in the global oceans based on 23 years of altimetry data. Multicore structures were identified using an improved geometric closed-contour algorithm of sea surface height. Splitting and merging events were discerned from continuous time series maps of sea level anomalies. Multicore structures represent an intermediate stage in the process of eddy evolution, similar to the generation of multiple nuclei in a cell as a preparatory phase for cell division. Generally, splitting or merging events can substantially change (by a factor of 2 or more) the eddy scale, amplitude, and eddy kinetic energy. Specifically, merging (splitting) generally causes an increase (decrease) of eddy properties. Multicore eddies were found to tend to split into two eddies with different intensities. Similarly, eddy merging is not an interaction of two equal-intensity eddies, and it tends to manifest as a strong eddy merging with a weaker one. A hybrid tracking strategy based on the eddy overlap ratio, considering both multicore and single-core eddies, was used to confirm splitting and merging events globally. The census revealed that eddy splitting and merging do not always occur most frequently in eddy-rich regions; e.g., their frequencies of occurrence in the Antarctic Circumpolar Current and western boundary currents were found to be greater than in midlatitude regions (20–35∘) to the north and south. Eddy splitting and merging are caused primarily by an unstable configuration of multicore structures due to obvious current– or eddy–topography interaction, strong current variation, and eddy–mean flow interaction.
Highlights
Mesoscale eddies are large bodies of swirling water, which generally refer to ocean signals with spatial scales of tens to hundreds of kilometers and temporal scales of days to months (Robinson, 2010)
By combining satellite altimetry and Argo profiling float data, Zhang et al (2014) found that eddy-induced zonal mass transport was comparable in magnitude to that of the large-scale wind- and thermohalinedriven circulation, which suggested mesoscale eddies have a strong impact on global climate change and air–sea interaction
Similar to the discussion regarding the lifetimes of multicore eddies, a multicore eddy trajectory might split into two single-core eddies that persist for only a few days
Summary
Mesoscale eddies are large bodies of swirling water, which generally refer to ocean signals with spatial scales of tens to hundreds of kilometers and temporal scales of days to months (Robinson, 2010). Laxenaire et al (2018) proposed an original assessment on Agulhas rings, whose novelty lies in the detection of eddy splitting and merging events, and they found these events are abundant and significantly impact the concept of a trajectory associated with a single eddy Such studies considered an eddy at one moment as a single eddy entity, which was split into two separate eddies at the moment, without consideration of eddy–eddy interaction processes. Based on SLA data acquired over a 23-year period (January 1993 to December 2015), this study used a threshold closed-contour algorithm to identify mesoscale eddies and multiple eddies within the global oceans.
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