A Census of Gulf Stream Warm and Cold Core Rings (1980-2017)

Adrienne Silver, University of Massachusetts Dartmouth, New Bedford, MA, United States, Avijit Gangopadhyay, Professor of Oceanography, School for Marine Science and Technology University of Massachusetts Dartmouth 836, S. Rodney French Blvd. New Bedford, MA, New Bedford, MA, United States, Nishchitha S Etige, Boston University, Earth and Environment, Boston, MA, United States, Glen Gawarkiewicz, Woods Hole Oceanographic Institution, Woods Hole, MA, United States, James J Bisagni, SMAST/UMass Dartmouth, Fairhaven, MA, United States, Mahmud Monim, RPS Group - Ocean Sciences, S Kingston, RI, United States and Jenifer Clark, Jenifer Clarks Gulfstream, Dunkirk, MD, United States
Abstract:
A census for Warm Core Rings (WCRs) in the Gulf Stream (GS) region is presented based on 38 years (1980-2017) of data. The census was first developed to document the dates and locations of formation and dissipation of WCRs, and their sizes at formation in four 5-degree areas between 75°W and 55°W. Regionally, more than two-thirds of the ring formations occurred to the east of 65°W. The age and size distribution show progressively more rings with higher longevity and greater size when formed to the east of 70°W. Summer maxima and winter minima are significant signatures of the seasonality of WCR formation. Over the 38-year period of study, a clear regime shift occurred during 2000 and was pervasive in all four areas. The WCR formation over the whole region (75-55W) increased from an average of 18 per year during regime 1 (1980-1999) to 33 per year during regime 2 (2000-2017). While the regime shift did not have any significant effect on the size distribution; the average age of the WCRs in all four areas decreased by 20-40% depending on areas and/or seasons from regime 1 to regime 2. The ring occupancy index, a first-order signature of impact of the WCRs on the slope, increased significantly for all areas from regime 1 to regime 2, with highest increase in area 1, indicating relatively larger increased instability in the recent years. The results from the WCR census are then compared and contrasted with the results from the associated Cold Core Ring (CCR) census to get a better understanding of the overall dynamics of the GS. Warm and Cold Core Ring formations show stark differences in seasonality and in inter-annual trends. Possible causes and the implications of such differences over seasonal and longer time-scales are explored.
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