2014-2017 Anomalous Loop Current Activity

摘要

The years 2014-2017 marked a period of anomalous and extreme Loop Current (LC) activity that resulted in significant impact on offshore operations for the first 18 months, followed by a 4- to 6-month period of more typical behavior and then 15 months of uncharacteristic inactivity. The objectives of this study are to (i) provide a detailed description of the kinematic structure of the Loop Current Eddies (LCEs) observed during this time frame; (ii) determine the vertical extent of each eddy and the effect of eddy activity on near-bottom currents, and (iii) establish a relationship (if any) between eddy activity and intensity of inertial oscillations within the water column. We present data collected from ADCPs at several locations in the northern Gulf of Mexico along with an extensive network of drifting buoys in correlation with daily frontal analyses and a comparison with historical events. To estimate the intensity of inertial oscillation and its variability in time, we computed rotary current spectra for periods characterized by high and low eddy activity. While circulation patterns during early 2014 were fairly typical, an apparent sudden increase in energy marked the beginning of hyperactivity in late June. Eddies Lazarus, Michael, Nautilus, and Olympus spun off the LC, each eddy experiencing multiple reconnections with the LC before its final separation in addition to amplified intensities (over 3 knots, max 4.5+ knots). December 2015 marked the beginning of the second phase. Another eddy (Poseidon) separated from the LC in April 2016; however, the winding down process of the LC circulation was already in effect. Poseidon did not exhibit a significant northward migration and the LC itself remained far south. In the central Gulf, the passage of Poseidon was followed by the passage of a subsurface cyclonic eddy, without a significant surface expression, propagating westward. For the next 18 months, the LC remained extremely inactive. While currents in the near-bottom layer were not directly correlated with the flows in the upper part of the water column during the period of the high eddy activity, the later period was characterized by more energetic near-bottom flows, suggesting LCE's may stimulate generation of topographic Rossby waves that cause strong near-bottom intensities. No significant correlation between the presence of LCE's and intensity of inertial oscillations was found. Results of recent near-surface and water column current observations are presented in the paper.