Evolution and kinematics of a loop current eddy in the Gulf of Mexico during 1985

Abstract

The large eddy that broke off from the Loop Current in July 1985 was the most extensively studied eddy ever to appear in the Gulf of Mexico. Other investigators have described its early evolution based on Lagrangian drifters and its later evolution using moored current meters in the western gulf. This paper provides additional insight on the early evolution of the eddy using results from air dropped expendable bathythermographs and air dropped expendable current profilers in early May, a hydrographic ship survey in mid July, and a detailed ship survey in August using expendable bathythermographs and a current profiler. The May survey established a center of circulation at about 26øN but showed that the eddy had not separated from the Loop Current. A maximum velocity of 171 cm/s was observed near the northern edge .of the feature. The evidence suggests that a large elongated eddy then separated from the Loop Current and later split into two smaller eddies. The July hydrographic cruise showed a clear separation of the large eddy from the Loop Current to the southeast. Two weeks later, the August survey showed an asymmetric eddy, with the maximum surface current 178 cm/s south of the center of circulation and 132 cm/s to the north. A wes. tern eddy named Ghost Eddy then separated from an eastern eddy named Fast Eddy. Using the c•.ent profiles and data from the ch-ifters, we constructed a simple kinematic feature model for eddies in the Gulf of Mexico.

Varying mesoscale structures influence larval fish distribution in the northern Gulf of Mexico

“…The LC returns to its southern location, where water from the Yucatan Current flows more directly toward the Straits of Florida, after the northern extension of the LC is pinched off. This process forms large anticyclonic rings which then propagate westward at speeds of 2 to 5 km d −1 , with a lifetime of days to ~1 yr (Elliott 1982, Forristall et al 1992, Shay et al 1998. These anticyclonic rings have radii of ~150 km and swirl speeds of 1.8 to 2 m s −1 and can reach ~800 m depth (Oey et al 2005).…”

Drifter motion in the Gulf of Mexico constrained by altimetric Lagrangian coherent structures

“…Plumes like this occur regularly, possibly strongly influenced by the evolving mesoscale field [Morey et al, 2005], which is dominated by the episodic shedding of Loop Current rings [Forristall et al, 1992]. The centerpiece of the chlorophyll plume is well represented by attracting LCS (black curves) extracted from altimetry using the methodology described below.…”

Hyperbolicity in temperature and flow fields during the formation of a Loop Current ring

“…LCRs have velocities exceeding 1 m s −1 and may have diameters exceeding 200 km. Indest et al (1989), Lewis et al (1989), Forristall et al (1992), and Glenn and Ebbesmeyer (1993) provided early comprehensive summaries of the characteristics of these structures. See Sturges et al (2005) and for recent synopses of these features and their roles in the general circulation of the Gulf.…”