DOI: 10.5281/zenodo.15186223
title: Cold Eddy Trajectories in the Northwest Atlantic Sargasso Sea (2017-2023)

description: This dataset consists of weekly trajectory information of Gulf Stream Cold Eddies (CE) that existed between 2017 and 2023.

The format of this Cold Eddy dataset is similar to the Warm Core Ring (WCR) Trajectory data from Porter et al. (2022, 2024) and Silver et al. (2022), and the following description is adapted from those datasets. This dataset is comprised of individual files containing each eddy’s weekly center location and its surface area for 181 CEs that existed and were tracked between January 1, 2017 and December 31, 2023 (28 CEs formed in 2017; 24 formed in 2018; 25 formed in 2019; 26 formed in 2020; 35 formed in 2021; 23 formed in 2022; and 20 formed in 2023). Each Cold Eddy is identified by a unique alphanumeric code 'CEyyyymmddX', where 'CE' represents a Cold Eddy (as identified in the analysis charts); 'yyyymmdd' is the year, month and day of formation; and the last character 'X' represents the sequential sighting (formation) of the eddy in that particular year. Continuity of an eddy which passes from one year to the next is maintained by the same character in the previous year and absorbed by the initial alphabets for the next year. For example, the first eddy formed in 2021 has a trailing alphabet of 'J', which signifies that a total of nine eddies were carried over from 2020 which were still present on January 1, 2021 and were assigned the initial nine alphabets (A, B, C, D, E, F, G, H, and I). Each eddy trajectory has its own netCDF (.nc) filename following its alphanumeric code. Each file contains 4 variables every week, “Lon”- the eddy center’s longitude, “Lat”- the eddy center’s latitude, “Area” - the eddies size in km^2, and “Date” in days – which is the number of days since Jan 01, 0000. Note that in this dataset, which ended tracking all eddies up to 2023, there were six eddies that formed in 2023, and were carried over into 2024 were included with their full trajectories going into the year 2024. These eddies are: ‘CE20230515P’, ‘CE20230818U’, 'CE20230925V', 'CE20231030Y', 'CE20231103Z', and 'CE20231106a'.

Findings from Jensen et al. (2024) suggest three different cyclonic eddy formation types: pinch-off cyclonic rings, hook-type cyclonic eddies, and Sargasso Sea cyclonic eddies. Pinch-off cyclonic rings form from a Gulf Stream meander trough amplifying, then encircling Slope Sea water and eventually detaching from the Gulf Stream as a cyclonic cold-core ring in the Sargasso Sea. Hook-type eddies form from a southward extending filament of the southern flank of the Gulf Stream establishing as a hook-like entity cyclonically encircling a body of Sargasso Sea water at its core. Sargasso Sea cyclonic eddies are isolated from the Gulf Stream and occur in the Sargasso Sea. A separate file is also created to help identify the cold eddy's formation type.

Two files are provided here. These are:

(1)  The trajectories of all Gulf Stream Cold Eddies formed from 2017 to 2023. Filename – CE_2017_2023_ncfiles.zip

(2)  Information on the formation type of each Cold Eddy. Filename – CE_FormationTypes_2017to2023.doc

The process of creating the CE weekly tracking dataset follows the same GIS-based methodology of the previously generated WCR census (Gangopadhyay et al., 2019, 2020). The Jenifer Clark’s Gulf Stream Charts described in Gangopadhyay et al. (2019), and continued through 2023 were used to create this dataset and were available 2-3 times a week from 2017-2023. Thus, we used approximately 840+ Charts for the 7 years of analysis. All of these charts were reanalyzed between 75°W and 55°W using QGIS 2.18.16 (2016) and geo-referenced on a WGS84 coordinate system (Decker, 1986). A single eddy trajectory is then obtained following an eddy through all of the available charts during the eddy's lifespan on a weekly basis. This process is repeated for every individual eddy.