Changes in the Loop Current's Eddy Shedding in the Period 2001–2010

A major change in the Loop Current's eddy shedding was found in the decade 2001–2010. Sixteen (16) rings separated from the Loop Current in that decade, whereas in two previous decades, 11 rings separated in each decade. More than half the rings (i.e., 56%) that separated from the Loop Current in the decade 2001–2010 had separation periods ≤8 months. In the period prior to 2001, only 26% of the rings had separation periods ≤8 months. Furthermore, the dataset average period for ring separation for the period prior to 2001, an average over a 29-year period, was about 11 months, and the dataset average Loop Current's westward tilt angle—a factor that indicates whether the Loop Current will soon shed an eddy or not—was about 16°. After the year 2000, the dataset average period for ring separation, an average over a 39-year period, decreased by about 1 month and was about 10 months. The average ring-separation period in the decade 2001–2010 was about 9 months. The dataset average of the Loop Current's westward tilt angle increased by about 5° in the period 1998–2008 and was about 20° in 2010. Potential causes for these changes are discussed. 1. Introduction Previous studies of the cycle of warm-core ring (WCR) separation from the Loop Current have reported average separation periods of about 11-12 months [1–6]. Studies have found that the frequency distribution is bimodal with modes at 8-9 months and 13-14 months [7, 8] and with modes at 6 and 11 months [5, 6]. Vukovich [2, 4, 6] also noted that the eddy separation periods were highly variable, ranging from 6 to 19 months. Sturges and Evans [1] have suggested that the maximum period between ring separations maybe as large as 30 months, but periods that large have not been observed as yet. The minimum eddy-shedding period previously observed was 8 months [1, 9]. Vukovich [6], using a 32-year data set, found that the minimum eddy-shedding period was 6 months. Vukovich [6] introduced the concept of the Loop Current orientation. The Loop Current orientation was defined as the westward tilt angle of the Loop Current. The westward tilt of the Loop Current is believed to be the result of a ring that develops within the Loop Current, but has not as yet separated from the Loop Current. The ring drifts westward, bringing the Loop Current with it, so to speak, which causes the Loop Current’s westward tilt angle to increase. This processes continues until the ring separates from the Loop Current. Some of the initial westward tilting of the Loop Current may be due to the presents of the West Florida Shelf, but the larger