Nesting the Gulf of Mexico in Atlantic HYCOM: Oceanographic processes generated by Hurricane Ivan

https://doi.org/10.1016/j.ocemod.2007.12.002Get rights and content

Abstract

The HYbrid Coordinate Ocean Model (HYCOM) has been configured for the Gulf of Mexico (GOM) at 1/25° horizontal grid resolution and has been nested inside a basin-scale 1/12° Atlantic version of HYCOM. The 1/25° nested GOM model is used to study temperature variations, current patterns, transport variations, and two coastal-trapped waves (CTWs) generated by Hurricane Ivan during mid September 2004. The model results indicate that the winds generated by Ivan: (1) induced a transport variation of approximately 2 Sv/day along the Yucatan Channel, (2) enhanced the oceanic mixing lowering the sea surface temperature more than 3 °C along Ivan’s path, (3) produced a thermocline vertical velocity of >100 m/day, and (4) generated a westward transport of ∼8 Sv along the northern coast of the GOM that was redirected by the Louisiana coastline inducing a southward transport of ∼6 Sv. Throughout its passage over the Caribbean Sea Ivan generated first a CTW along the south east coast of Cuba. After its generation this wave propagated along the coast and partially propagated along the western tip of the Cuban Island and continued its propagation along the northern coast of the Island. The model existence of CTWs along the coast of Cuba is reported for the first time. Later on, over the Florida–Alabama–Mississippi–Louisiana coast, Ivan’s westward winds drove a model oceanic onshore transport and generated a strong coastal convergence. The convergence raised the sea surface height ∼90 cm generating a second CTW, which is characterized by alongshore and cross-shore scales of ∼700 and ∼80 km, respectively. The CTW current pattern includes westward surface currents of more than 2.0 m/s. After its generation, the wave weakened rapidly due to Ivan’s eastward winds, however a fraction of the CTW propagated to the west and was measured by a tide gauge at Galveston, Texas. The descriptions, hypothesis, and discussions presented in this study are based on model results and those results are compared and validated with sea surface height coastal tide gauge observations and sea surface temperature buoy observations.

Introduction

The cyclone that became Ivan was classified as a tropical depression on September 2, 2004. At that time the cyclone was located in the middle of the Tropical Atlantic Ocean near 29.10°W--9.70°N and featured maximum sustained winds of ∼13 m/s. During the following two weeks Ivan traveled through the Caribbean Sea and the GOM strengthening its maximum sustained winds to ∼75 m/s, and generating wind waves with amplitude of ∼27 m in the northern GOM (http://www.nhc.noaa.gov; Wang et al., 2005).

Ivan entered into the GOM on September 14, 2005, with wind speeds >60 m/s through the Yucatan channel (Fig. 1) providing strong wind-forcing for both the real GOM ocean and the GOM numerical ocean models, supplying surface boundary conditions for those models, and challenging the GOM models to accurately simulate the response to the strong and rapidly propagating Ivan wind system. The results of this study show that: (1) Two CTWs were generated by Hurricane Ivan. One of them was generated along the coast of Cuba and the other along the Florida–Alabama–Mississippi–Louisiana coast. The model generation of a CTW along the coast of Cuba is reported for the first time. (2) GOM buoys recorded sea surface temperature (SST) decreases of >3 °C in ∼2 days as an upper ocean response to Ivan’s winds. That strong and rapid ocean reaction to the Hurricane wind forcing is an excellent test case to examine the capabilities of mixed layer sub-models to simulate rapid cooling events. Thus five different mixed layer sub-models (which are embedded in HYCOM) were used to investigate the SST evolution during the year 2004. (3) The deterministic (which is considered here as the direct response to atmospheric and remote forcings), and nondeterministic (which is attributed to nonlinear mesoscale flow instabilities) regions of the GOM are calculated and are used to explain the differences between modeled and observed sea surface height.

Section snippets

HYCOM configurations

HYCOM is the HYbrid vertical Coordinate Ocean Model, which is isopycnal in the open stratified ocean, terrain-following in shallow coastal regions, and z-level in mixed layer and unstratified regions. This generalized vertical coordinate approach is dynamic in space and time via the layered continuity equation that allows a smooth dynamical transition between the coordinate types. HYCOM (Bleck, 2002) was developed from the Miami Isopycnic Coordinate Ocean Model (MICOM) using the theoretical

Results and discussion

The description and discussion presented in this section is based on model results and the model results are compared and validated with SSH coastal tide gauge observations and SST buoy observations.

Summary and concluding remarks

The ocean response to Hurricane Ivan is studied using a 1/25° grid resolution GOM configuration of HYCOM that is nested inside of an eddy-resolving (1/12° equatorial resolution) North Atlantic configuration of HYCOM. The nested GOM approach allows direct examination of the connectivity of the GOM with the North Atlantic Ocean at high resolution and relatively low computational cost and permits the free propagation of hurricanes and hurricane generated signals (like eddies and currents) from the

Acknowledgments

This is a contribution to the 6.2 project Coastal Ocean Nesting Studies (CO-NESTS) under program element 0602435N, and to the Slope to Shelf Energetics and Exchange Dynamics (SEED) project under program element number 0601153N, both funded by the Office of Naval Research (ONR). The GOM simulations were performed under the Department of Defense High Performance Computing Modernization Program on an IBM P4+ computer at the Naval Oceanographic Office, Stennis Space Center. The Atlantic simulations

References (36)

  • Chassignet, E.P., Hurlburt, H.E., Smedstad, O.M., Halliwell, G.R., Hogan, P.J., Wallcraft, A.J., Baraille R., Bleck,...
  • P. Hamilton et al.

    Transports through the Straits of Florida

    J. Phys. Oceanogr.

    (2005)
  • H.E. Hurlburt et al.

    A numerical study of Loop Current intrusions and eddy-shedding

    J. Phys. Oceanogr.

    (1980)
  • H.E. Hurlburt et al.

    Statistical inference of weakly correlated subthermocline fields from satellite altimeter data

    J. Geophys. Res.

    (1990)
  • W.E. Johns et al.

    Annual cycle and variability of the North Brazil Current

    J. Phys. Oceanogr.

    (1998)
  • A.B. Kara et al.

    A new solar radiation penetration scheme for use in ocean mixed layer studies: An application to the Black Sea using a fine resolution HYbrid Coordinate Ocean Model (HYCOM)

    J. Phys. Oceanogr.

    (2005)
  • A.B. Kara et al.

    How does solar attenuation depth affect the ocean mixed layer? Water turbidity and atmospheric forcing impacts on the simulation of seasonal mixed layer variability in the turbid Black Sea

    J. Clim.

    (2005)
  • A.B. Kara et al.

    Sea surface temperature sensitivity to water turbidity from simulations of the turbid Black Sea using HYCOM

    J. Phys. Oceanogr.

    (2005)

    • Cited by (0)

    View full text
    Published by Elsevier Ltd.