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Downstream of Cape Hatteras, the vigorously meandering Gulf Stream forms anticyclonic warm core rings (WCRs) that carry warm Gulf Stream and Sargasso Sea waters into the cooler, fresher Slope Sea, and forms cyclonic cold core rings (CCRs) that carry Slope Sea waters into the Sargasso Sea. The Northwest Atlantic shelf and open ocean off the U.S. East Coast have experienced dramatic changes in ocean circulation and water properties in recent years, with significant consequences for marine ecosystems and coastal communities. Some of these changes may be related to a reported regime shift in the number of WCRs formed annually, with a doubling of WCRs shed in the years after 2000. Since the regime shift was detected using a regional eddy-tracking product that is primarily based on sea surface temperatures from satellites and in-situ measurements and relies on analyst skill, we examine global eddy-tracking products as an automated and potentially more objective way to detect changes in Gulf Stream rings. Available global eddy tracking products rely on altimeter-measured sea surface height (SSH), with anticyclonic WCRs registering as sea surface highs and cyclonic CCRs as lows. To identify ocean eddies, these products use either contours of SSH or a Lagrangian approach with particles seeded in satellite-based surface geostrophic velocity fields (based on SSH gradients). Comparisons of these products with the regional SST-based product include annual WCR counts, seasonality, preferred formation location, regime shift detection, and several years of feature-to-feature WCR comparisons across products. This study confirms that the three global eddy products are not well suited for statistical analysis of rings shed from the Gulf Stream, a highly energetic region, and suggests that automated WCR identification and tracking comes at the price of accurate identification and tracking.

Gangopadhyay et al., 2019 found a regime shift in the number of warm core rings formations between 1980–1999 and 2000–2017. Silver et al., 2021 expanded upon this work and also found a regime shift in warm core rings, but no regime shift in cold core rings. We seek to understand if a regime shift, and similar results, can be detected using a global mesoscale eddy dataset such as META2.0.

☆The Altimetric Mesoscale Eddy Trajectories Atlas (META2.0)
The primary dataset used in this notebook is The Altimetric Mesoscale Eddy Trajectories Atlas (META2.0). Schlax & Chelton, 2016 give a product description of META2.0, which built upon Chelton et al., 2011.

The Mesoscale Eddy Trajectories Atlas (META3.1EXP)
The Mesoscale Eddy Trajectories Atlas Product Verison 3.1 Experimental (META3.1EXP) was first published in March 2022 and is an update to META2.0. The details of this product are described in Pegliasco et al., 2022 which inherited an eddy-tracking algorithm developed by Mason et al., 2014 that is inpsired by Chelton et al., 2011.

The Global Lagrangian Eddy Dataset (GLED v1.0)
The third eddy product differs from the META datasets because it uses Lagrangian methods to identify and track eddies. This dataset was created by Liu and Abernathy, 2023 as the Lagrangian alternative to Eulerian eddy products like META2.0 and all the successive Eulerian eddy products inspired by Chelton et al., 2011.

Yearly census of Gulf Stream Warm Core Ring formation from 1980 to 2017
The WCR census uses the Clark charts to document the formation and demise dates, locations, and the area at formation for all WCRs formed between 1980 and 2017 that lived for a week or more.