Death of three Loop Current rings

Abstract

The life cycle of large anticyclonic rings in the Gulf of Mexico (GOM) is widely described by pinch off from the Loop Current, migration across the Gulf and eventual spin down along the western slope. Extensive observational and modeling efforts provide a relatively consistent picture of rings pinching off from the Loop Current and of complex interaction between anticyclones and cyclones driven by bathymetry along the western and northwestern shelf. The observational record for Loop Current rings (LCRs) during the intermediate period of westward translation is less clear. A number of studies recognize distinct anomalies in LCR characteristics in deep water as the rings enter the western Gulf near 92-94W. These include abrupt changes in the geometry of observed drifter trajectories and derived eddy parameter fits as well as changes in both ring translation speeds and the estimated rate of ring decay. Such observations are consistent with intense interaction and mass exchange between the rings and other coherent mesoscale features known to be present in the western Gulf. We test the hypothesis that interactions with the ambient mesoscale field can lead to rapid loss of coherence of some LCRs well before they reach the 'eddy graveyard' in the western Gulf. We use the data-assimilating, eddyresolving numerical GOM model described by Kantha et al. (2005) to assess the fates of readily identified LCRs Fourchon, Juggernaut, and Millenium during the period July 1998 to August 2001. Lagrangian metrics, including relative dispersion of small drifter clusters seeded in the ring cores, analysis of evolving blobs seeded in the ring cores, and finite-scale Lyapunov exponents, are used to track model ring evolution. These metrics clearly show that interactions with existing mesoscale cyclones and anticyclones caused Fourchon and Juggernaut to break up near 92W on advective time scales. In addition, Millenium also experienced an intense deformation, stirring, and mixing episode near 92W. Blob studies showed that the core fluid of Millenium was ultimately dispersed over much of the western basin. Our results show that some LCRs may break up through interactions with existing western Gulf cyclones and anticyclones prior to reaching the western slope.

Ocean Circulation in the Western Gulf of Mexico Using Self‐Organizing Maps

“…This frequency corresponds to the LCE lifespan across the GoM once completely separated from the LC system. Displacement velocities of ~3–5 km/day, as suggested by Lipphardt et al (), match the approximate annual periodicity. The high power spectral density during the 2000–2002 period is associated with LCE Juggernaut (2000), Millennium (2001) and Pelagic (2002).…”

Hydrography of the Central and Western Gulf of Mexico

“…Besides being the main conveyance of the water masses of remote and Caribbean origin into the GoM, the LCEs play a major role in its thermohaline circulation through the westward transport of heat, salt, and momentum (Elliott, 1982;Lewis & Kirwan, 1985;Lipphardt et al, 2008) and in the horizontal redistribution of the river plumes (Jochens & DiMarco, 2008;Morey, Martin, et al, 2003;Morey, Schroeder, et al, 2003). The signature of the Mississippi River water has been found hundreds of kilometers away from the discharge region (Morey, Martin, et al, 2003); this freshwater is an important source of variability of the water masses within the upper few tens of meters of the water column (Jochens & DiMarco, 2008).…”

Application of the smooth orthogonal decomposition to oceanographic data sets

“…As the study area is dramatically influenced by the presence of the loop‐current [ Hamilton et al , ; Lipphardt et al , ; Oey , ; Jochens and DiMarco , ; DiMarco et al , ], satellite altimetry of the area was used to identity “forcing regimes.” During the time interval studied (July 2012 to July 2013) the geostrophic forcing may be separated into five regimes: (i)July to mid‐August → east to west zonal flow, (ii) mid‐August to mid‐September → storm track of Hurricane Isaac crossed the array, (iii) mid‐September to mid‐February → development of an anticyclonic circulation, (iv) mid‐February to mid‐April → strong down coast (along topography) flow, and (v) mid‐April to July → development of an cyclonic circulation.…”