What do we know and what can we predict about the timing of Loop Current eddy separation?
Colorado Center for Astrodynamics Reserach,
Boulder, CO 80309-0431,
The ability to accurately predict the time that a Loop Current eddy (LCE) will ultimately separate from the Loop Current (LC) has become a grail of sorts in Gulf of Mexico oceanography, and for good reason. Approximately 30% of the crude oil and 20% of the natural gas produced in the U.S. comes from the Gulf of Mexico, much of it from the continental slope and deepwater of the north-central Gulf. Strong LC and LCE currents affect day-to-day operations during offshore oil and gas exploration activities, frequently shutting down operations and making planning and scheduling difficult for this very expensive enterprise. The LC and LCEs also play an active role in the rapid intensification of Gulf of Mexico hurricanes. This was the case in Hurricanes Katrina and Rita, both of which intensified over the intruded LC and reached Category 5 before making landfall along the northern Gulf coast. Clearly if LC intrusion and eddy separation could be predicted a year or even just months in advance there could be significant socioeconomic benefits. Efforts along these lines, using operational data-assimilative nowcast/forecast ocean models, have not been very successful. This is because the LC is an inherently unstable current system in which the dominant processes affecting intrusion and separation are not clearly understood, making accurate forecasting using numerical models very difficult. A review of the 15-year altimetric record of LC metrics and comparisons with the LC penetration and eddy separation cycles, however, suggest that there may be a more fundamental controlling influence on LC eddy separation. The statistics show a clear relationship between the LC retreat after eddy separation and the time that a large LC eddy will ultimately separate during the next LC intrusion cycle. The 15-years of LC intrusion LCE separation statistics and a proposed statistical approach to predicting the timing of subsequent LCE separation based on LC retreat after eddy separation will be discussed, as well as potential applications to operational planning and hurricane forecasting.