Transcript Fig.1 - University of South Florida

Storm-Induced Circulation on the Meso-American Barrier Reef System
during Hurricane Mitch:
Coupling Remote Sensing Data and a Nested-Grid Ocean Circulation Modeling System
Liang Wang, Chuanmin Hu and Frank Muller-Karger, IMARS, College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA
Jinyu Sheng, Department of Oceanography, Dalhousie University, Halifax, NS B3H 4J1, Canada
Serge Andrefouet, Institute de Researche pour le Developpement, BP A5 – 98848 Noumea cedex, Nouvelle Caledonie
Bruce Hatcher, Marine Ecosystem Research, Cape Breton University, Sydney, NS B1P 6L2, Canada
Background
CANDIE stands for Canadian version of Diecast
• The Meso-American Barrier Reef System
(MBRS) in the northwestern Caribbean Sea is
one of large barrier reef ecosystems in the
world.
• Coral reefs and associated ecosystems in the
MBRS provide important habitat, breeding and
feeding grounds for a great diversity of marine
invertebrates, fish, reptiles and mammals
(Kramer and Kramer, 2002).
Fig.1
MBRS
Fig.1
Characteristics of the Caribbean Sea

Reefs of the MBRS have been negatively
affected by various disturbances and stresses
resulting from human activities and natural
events in the region over the last 30 years. The
outcomes include epidemics of coral disease,
coral bleaching, overgrowth by macro-algae,
decimation of fish abundances and intense as
well as widespread physical destruction.
 Understanding cause and effect and predicting
impacts demands better knowledge of the
interacting physical, ecological and biological
processes that connect and sustain the marine
ecosystems of the MBRS.
Simulated Sea Surface Temperature (SST) and storm-induced SST (T(Clim+Storm) – T(Clim) )
A triply nested-grid modeling system based on CANDIE
 The largest marginal sea of the
Atlantic Ocean, separated from the
Atlantic basin by an islandstudded enclosure (Fig. 1).
 Little seasonal variation in
surface water temperatures (25 to
28o C). Stratified in the upper 1200
m and vertically uniform below
2000 m.
 Under the influence of NA trade
winds (westward).
 Dominated by a through-flow
known as the Caribbean Current in
the upper ocean.
(Sheng et al. , 1998; Lu et al., 2001; Sheng et
al., 2001; Zhang et al., 2001; Sheng and Tang, 2004; Sheng and Wang, 2004; Wang et al., 2005):
 3D,  z-level model,  implicit free-surface,  fourth-order numerics.
The nested modeling system has three sub-components with different horizontal resolutions:
an outer model (20 km), a middle model (6 km), and an inner model (2 km). 28 z-levels: 2 m for
top ten levels and gradually increased level thickness to 500 m near bottom.
The semi-prognostic method (Sheng et al., 2001) is used in this study to reduce model drift.
The newly developed nesting technique based on the semi-prognostic method was used.
The system is forced by the NCEP wind and idealized wind forcing associated with a moving
Fig. 6
Fig. 7
Simulated sea surface salinity and satellite-derived ocean color along the north coast of Honduras
The nested modeling system reproduces reasonably well the river plumes due to abnormal precipitation along the north
coast of Honduras During Hurricane Mitch. The simulated pattern of river plume characterized by the lower salinity water
are very comparable to the pattern characterized by ocean color in SeaWIFS images.
storm.
Nested-grid modeling system
Wind forcing associated with a moving storm
rmax rmin 1 1
 
τ r, (r,  )   | τ r, |m
rmax  rmin r rmax
τ r, (r,  )   | τ r, |m
τ r, (r,  )  0
Fig. 4
r
rmin

rmin  r  rmax
Fig. 8
r  rmin
r  rmax
Fig. 9
Dispersion of near-surface particles during Hurricane Mitch
The particle tracers are seeded initially in four areas near the sea surface of the MBRS before Hurricane Mitch significantly
affects the region. The dispersion of particle tracers during Hurricane Mitch demonstrates the important hydrodynamic
connectivity of surface waters in the MBRS.
Simulated Currents during Hurricane Mitch
MAIN OBJECTIVES of this study are: (a) to develop a nested-grid circulation
model for the MBRS; (b) to use the model to predict the effect of a major
weather disturbance (Hurricane Mitch) on the circulation and density field in
the region; and (c) to compare the predicted outcomes with remotely sensed
data for model validation.
Fig. 10a
Fig. 2
Fig. 3
Fig. 10d
The triply-nested grid model simulation resolves key aspects of circulation of the upper ocean in the west Caribbean Sea
Fig.
Fig.
5b5b
Fig. 5a
 Mitch skirted the coasts of Nicaragua
and Honduras, making landfall on 29th
October, 1998.
 Mitch is among the five strongest
storms on record in the Atlantic Basin and
generated significant coastal flooding
and landslides.
Fig. 10c
Conclusions
At 1 m
Hurricane Mitch (October – November, 1998)
 Mitch started as a tropic depression on
22 October, 1998 and strengthened to a
Category 5 storm by 26 October with the
maximum sustained wind speeds of 155
knots (Figs. 2 and 3).
Fig. 10b
in response to Hurricane Mitch in 1998.
The nested-grid modeling system generates strong currents on the upper ocean (Fig. 5) and significant sea surface
temperature cooling (Fig. 6 and 7) biased to the right of the storm track.
The simulated river plume transport characterized by the lower salinity water along the north coast of Honduras (Figs. 8
and 9) agrees well with a satellite-derived analysis by Andrefouet et al. (2002).
Dispersion of particle tracers (Fig. 10) demonstrates the important hydrodynamic connectivity of coral reef ecosystems in
MBRS during Hurricane Mitch.
Bibliography
At 75 m
Fig.
5c
Fig. 5c
Fig. 5d
 Andrefouet et al., 2002, Revising coral reef connectivity, Coral Reefs, DOI 10.1007/s00338-001-0199-0 21, 43- 48.
 Sheng, J., and L. Tang, 2003, A numerical study of circulation in the western Caribbean Sea, J. Phys. Oceanogr., 33, 2049-2069.
 Sheng, J., and L. Tang, 2004, A two-way nested-grid ocean-circulation model for the Meso-American Barrier Reef System, Ocean Dynamics, 54,
232-242.
 Tang, L., J. Sheng, B. G. Hatcher, and P. F. Sale, 2006, Numerical study of circulation, dispersion and hydrodynamic connectivity of surface
waters on the Belize shelf, J. Geophys. Res., in press.