Effects of winds and Caribbean eddies on the frequency of Loop Current eddy shedding: A numerical model study

[1] The Loop Current (LC) is known to shed eddies at irregular intervals from 3 to 17 months. The causes of this irregularity have not, however, been adequately identified previously. We examine the effects of various types of external forcing on shedding with a model of the western North Atlantic Ocean (96°–55°W, 6°–50°N). We force the model with steady transport at 55°W, with winds, and include eddies in the Caribbean Sea. We examine their separate effects. With steady transport only, the model sheds rings at a dominant period of 9–10 months. Wind-induced transport fluctuations through the Greater Antilles Passages cause shedding at shorter intervals (≈3–7 months). Caribbean eddies (anticyclones) cause shedding at longer periods (≈14–16 months). Potential vorticity conservation indicates that Caribbean eddies tend to deter northward extension of the LC into the Gulf, which can lead to longer periods between eddy shedding. Fluctuating inflow at the Yucatan Channel that is associated with winds and/or Caribbean eddies can cause an LC eddy to temporarily (∼1 month) detach from and then reattach back to the LC, a phenomenon often observed. Model results also suggest that southwest of Hispaniola, warm eddies are spun up by the local wind stress curl. This type of eddy drifts southwestward, then westward after merging with the Caribbean Current, and then northward as it progresses toward the Yucatan Channel; these eddies significantly affect the shedding behavior of warm-core rings. The timescale for spin up and drift from Hispaniola is about 100 days. Satellite data indicate the existence of these eddies in the real ocean.

[1]  R. D. Richtmyer,et al.  Difference methods for initial-value problems , 1959 .

[2]  Caskey,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS I . THE BASIC EXPERIMENT , 1962 .

[3]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[4]  G. Wüst,et al.  On the stratification and the circulation in the cold water sphere of the Antillean-Caribbean basins An abstract , 1963 .

[5]  G. Wüst.  Spreading and mixing of the water types : with an oceanographic atlas , 1964 .

[6]  A. Gordon.  Circulation of the Caribbean Sea , 1967 .

[7]  R. D. Richtmyer,et al.  Difference methods for initial-value problems , 1959 .

[8]  Alexandre J. Chorin,et al.  On the Convergence of Discrete Approximations to the Navier-Stokes Equations , 1969 .

[9]  J. Reid,et al.  Contributions on the Physical Oceanography of the Gulf of Mexico , 1972 .

[10]  K. Carder,et al.  Dissolved silica and the circulation in the Yucatan Strait and deep eastern Gulf of Mexico , 1977 .

[11]  H. Hurlburt,et al.  A Numerical Study of Loop Current Intrusions and Eddy Shedding , 1980 .

[12]  D. Roemmich.  Circulation of the Caribbean Sea: A well‐resolved inverse problem , 1981 .

[13]  J. Morrison,et al.  On the circulation of the western Gulf of Mexico with observations from April 1978 , 1981 .

[14]  D. Nof.  On the β-Induced Movement of Isolated Baroclinic Eddies , 1981 .

[15]  A. E. Gill.  Atmosphere-Ocean Dynamics , 1982 .

[16]  H. Hurlburt,et al.  A Numerical Model of Eddy Generation in the Southeastern Caribbean Sea , 1982 .

[17]  D. A. Brooks,et al.  A ship and satellite view of hydrographic features in the western Gulf of Mexico , 1982 .

[18]  T. Yamagata,et al.  On the Evolution of Nonlinear Planetary Eddies Larger than the Radius of Deformation , 1982 .

[19]  Sol Hellerman,et al.  Normal Monthly Wind Stress Over the World Ocean with Error Estimates , 1983 .

[20]  David C. Smith,et al.  The Interaction of a Two-Layer Isolated Mesoscale Eddy With Bottom Topography , 1983 .

[21]  George A. Maul,et al.  Cyclonic eddies in the eastern Gulf of Mexico , 1985 .

[22]  R. Corry,et al.  Seasonal Transport Variations in the Florida Straits: A Model Study , 1985 .

[23]  H. Hurlburt,et al.  Dynamic transfer of simulated altimeter data into subsurface information by a numerical ocean model , 1986 .

[24]  Alexandre Joel Chorin,et al.  On the Convergence of Discrete Approximations to the Navier-Stokes Equations* , 1989 .

[25]  R. Evans,et al.  The North Brazil Current retroflection: Seasonal structure and eddy variability , 1990 .

[26]  W. Teague,et al.  A Comparison Between the Generalized Digital Environmental Model and Levitus climatologies , 1990 .

[27]  George L. Mellor,et al.  A Gulf Stream model and an altimetry assimilation scheme , 1991 .

[28]  Robert L. Haney,et al.  On the Pressure Gradient Force over Steep Topography in Sigma Coordinate Ocean Models , 1991 .

[29]  Catherine A. Smith,et al.  An Intercomparison of Methods for Finding Coupled Patterns in Climate Data , 1992 .

[30]  Ping Chen,et al.  A model simulation of circulation in the northeast Atlantic shelves and seas , 1992 .

[31]  G. Forristall,et al.  Evolution and kinematics of a loop current eddy in the Gulf of Mexico during 1985 , 1992 .

[32]  P. Hamilton.  Lower continental slope cyclonic eddies in the central Gulf of Mexico , 1992 .

[33]  W. Schmitz,et al.  On the Effects of Horizontal Resolution in a Limited-Area Model of the Gulf Stream System , 1993 .

[34]  J. C. Evans,et al.  Separation of Warm-Core Rings in the Gulf of Mexico , 1993 .

[35]  P. Richardson,et al.  North Brazil Current retroflection eddies , 1994 .

[36]  David M. Fratantoni,et al.  Rings of the North Brazil Current: Their structure and behavior inferred from observations and a numerical simulation , 1995 .

[37]  Fred M. Vukovich,et al.  An updated evaluation of the Loop Current's eddy‐shedding frequency , 1995 .

[38]  W. Schmitz.  On the World Ocean Circulation. Volume 1. Some Global Features / North Atlantic Circulation. , 1996 .

[39]  L. Oey.  Simulation of Mesoscale Variability in the Gulf of Mexico: Sensitivity Studies, Comparison with Observations, and Trapped Wave Propagation , 1996 .

[40]  George L. Mellor,et al.  Simulations of the Atlantic Ocean with a free surface sigma coordinate ocean model , 1997 .

[41]  L. Oey.  Eddy energetics in the Faroe-Shetland channel: a model resolution study , 1997 .

[42]  Guillermo P Podesta,et al.  The Influence of Loop Current Perturbations on the Formation and Evolution of Tortugas Eddies in the Southern Straits of Florida , 1998 .

[43]  L. Oey,et al.  Sigma Coordinate Pressure Gradient Errors and the Seamount Problem , 1998 .

[44]  G. Mellor.  USERS GUIDE for A THREE-DIMENSIONAL, PRIMITIVE EQUATION, NUMERICAL OCEAN MODEL , 1998 .

[45]  R. Molinari,et al.  Direct observations of velocity and transport in the passages , 1999 .

[46]  J. O'Brien,et al.  The connectivity of eddy variability in the Caribbean Sea, the Gulf of Mexico, and the Atlantic Ocean , 1999 .

[47]  North Brazil Current Rings Experiment : surface drifter data report, November 1998-June 2000 , 2000 .

[48]  Patrick J. Hogan,et al.  Impact of 1/8° to 1/64° resolution on Gulf Stream model–data comparisons in basin-scale subtropical Atlantic Ocean models , 2000 .

[49]  T. Joyce,et al.  Water masses and circulation in the surface layers of the Caribbean at 66°W , 2000 .

[50]  Gilles Reverdin,et al.  Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2 , 2000 .

[51]  Robert R. Leben,et al.  Frequency of Ring Separations from the Loop Current in the Gulf of Mexico: A Revised Estimate , 2000 .

[52]  David M. Fratantoni,et al.  North Atlantic surface circulation during the 1990's observed with satellite-tracked drifters , 2001 .

[53]  J. Sheinbaum,et al.  Geostrophy via potential vorticity inversion in the Yucatan Channel , 2001 .

[54]  David M. Fratantoni,et al.  North Brazil Current Ring Generation and Evolution Observed with SeaWiFS , 2002 .

[55]  Lie-Yauw Oey,et al.  Deep Eddy Energy and Topographic Rossby Waves in the Gulf of Mexico , 2002 .

[56]  J. Sheinbaum,et al.  The potential vorticity flux through the Yucatan Channel and the Loop Current in the Gulf of Mexico , 2002 .

[57]  H. Simmons,et al.  The Squeezing of Eddies through Gaps , 2002 .

[58]  W. Johns,et al.  Velocity structure of North Brazil current rings , 2002 .

[59]  P. Hamilton,et al.  On the structure and motions of cyclones in the northern Gulf of Mexico , 2002 .

[60]  George H. Born,et al.  Operational Altimeter Data Processing for Mesoscale Monitoring , 2002 .

[61]  David M. Fratantoni,et al.  On the Atlantic inflow to the Caribbean Sea , 2002 .

[62]  J. Sheinbaum,et al.  Flow structure and transport in the Yucatan Channel , 2002 .

[63]  Hyun-chul Lee,et al.  The variability of currents in the Yucatan Channel: Analysis of results from a numerical ocean model , 2003 .

[64]  L. Oey,et al.  Near-Surface Currents in DeSoto Canyon (1997–99): Comparison of Current Meters, Satellite Observation, and Model Simulation , 2003 .