The role of cyclonic eddies in the detachment and separation of Loop Current eddies

Abstract. The Loop Current (LC) and its associated eddies, known as Loop Current Eddies (LCEs), are key oceanic features in the Gulf of Mexico. Using a statistical analysis of 29 years of satellite altimeter data (1993–2021), we show that more than half of the LCEs that detach from the LC reattach within 30 days and that only 42 % truly separate from the LC and move westward in the Gulf. Our observational analysis also shows that i) before a detachment can occur, the LC needs to extend far enough north in the Gulf to reach the Mississippi fan (∼27.5° N); ii) the ratio of separations to reattachments depends on latitude, with detachments being more prone to reattach if they occur south of 25° N and to separate if they occur north of 25° N; and iii) cyclonic eddies are consistently present during the detachment process, with one cyclonic eddy on the eastern side of the LC if the LCE is to reattach and one cyclonic eddy on each side of the LC if the LCE is to separate. In the latter case, the co-occurrence of eastern and western cyclonic eddies in the LC bottleneck zone forms a large cyclonic structure. This large cyclonic structure is often observed during separation events, and when it is absent, LCEs are more likely to reattach, indicating a potential role in modulating the LC extension into the Gulf of Mexico. Sometimes, it can restrict LC growth on time scales of several months. The observed associations between cyclonic eddies and LCE detachments provide a statistical framework that could help anticipate separation events.