EPISODIC METEOROLOGICAL EVENTS AFFECTING FLORIDA BAY
Principal Investigator:
Dr. Mark D. Powell
Collaborating scientist(s):
Dr. Mark DeMaria
Dr. Craig Mattocks
Samuel H. Houston
Eric Swartz
Paul Hebert
Objective:
The primary objective of this research project is to reconstruct
episodic/catastrophic meteorological events and local weather regimes
which critically affect the South Florida ecosystem.
Rationale:
Hurricanes, tropical storms and frontal passages are believed to exert
considerable influence on the health of Florida Bay. Wind fields associated
with these storms generate surface stress and an associated response in the
bay circulation patterns and sediment transport. Because the "multiple pond-bank"
nature of Florida Bay inhibits sediment transport forced by relatively
weak wind conditions, hurricanes are believed to play a critical role in
flushing the bay. Severe winds associated with tropical cyclones may
also contribute to ecosystem health as a result of the post-storm decay of
organic material damaged by the wind and storm surge. In order to assess
the response of Florida Bay to episodic wind events, circulation and
ecological modelers would benefit from wind field analyses based on
reconstruction of past events.
Method:
(1) Episodic Wind Field Reconstruction --
Gridded wind, precipitation, and temperature fields will be
generated from real case analyses, numerical model simulations, and
idealized scenarios described by canonical systems of analytical equations
to produce a catalog of datasets. Research scientists will be able to
quickly retrieve data from this event/regime archive for use in circulation
model simulations/predictions, hydrological modeling, natural systems
restoration, and biological impact studies. We plan to analyze the
most significant storms to affect Florida Bay over the past century.
In so doing we will attempt to show a variety of wind field affects
on Florida Bay which could comprise an archive of the types of
extreme events that can be expected over the next century. Data
will be processed to achieve a consistent framework in terms of
averaging time, height and exposure. For storms with few data
available the wind profile fit currently used in the SLOSH storm
surge model will be adapted to construct a background field. These
data will then be objectively analyzed using the Spectral
Application of Finite-Element Representation (SAFER) method
(Ooyama 1987, Lord and Franklin 1987). This method uses cubic
B-splines to minimize the difference between the input observations
and the analysis. The methods used to standardize the input data
for analysis are described in Powell et al., (1995), and Powell
and Houston (1995). The scale of the analysis is controlled by
the analyst depending on the features that need to be resolved.
Snap shots of the streamline and isotach fields for each storm
will be generated for a 2 x 2 degree lat-lon domain centered on
Florida Bay at 6-12 h intervals, depending on the translation
speed of the storm. This domain should also be suitable for those
interested in studying extreme wind affects on the southern end
of the Everglades. Images of the wind fields will be archived
on a World Wide Web site for access by other Florida Bay
researchers and gridded fields will be generated upon request.
These fields should be capable of import to geographical information
systems for correlation studies with other geo-referenced fields
such as mangroves, reefs, and turbidity plumes.
(2) Mesoscale Atmospheric Modeling --
A major component of this dataset construction effort is the use
of the Center for Analysis and Prediction of Storms'
Advanced Regional Prediction System (ARPS) cloud-/mesoscale
atmospheric numerical weather prediction model which can
simulate/predict surface winds, rainfall and thermodynamic
fields relevant to Florida Bay at high resolution. These
fields can be used as boundary conditions/forcing for bay
and ocean circulation models. The atmospheric model can
also be used to study the effect of specific processes on
the freshwater input to Florida Bay, such as
evaporation/precipitation under different weather
regimes, as well as the transport/rainout of toxic
atmospheric substances in the South Florida ecosystem.
Accomplishment:
In November of 1994, we hosted the South Florida Atmospheric
Modeling Workshop (NOAA, Nov. 1994), attended by 40 researchers
representing meteorology, hydrology and physical oceanography
from south Florida's research community. Attendees expressed
the need for a catalog of meteorological events/regimes which
critically affect the South Florida ecosystem. Gridded datasets
from this archive could be accessed for circulation/ecological
model simulations, hydrological modeling, natural systems
restoration, and biological impact studies. Based on this
need we began by reconstructing wind fields thataffected
Florida Bay during Hurricane Andrew of 1992 (Figure 1) and Hurricane
Gordon of 1994 (Figure 2).
The track of hurricane Andrew to the north of Florida Bay
may not have helped with flushing the bay. As shown by the
streamlines in the figure, the flow was dominated by
northwesterly and then southwesterly directions which
may have forced sediment to the northeast portion of the bay.
In addition, the strong winds in excess of hurricane force
along the north fringes of the bay damaged mangroves leading
to decay of large amounts of organic material in the northern
part of the bay. In contrast, the center of Tropical Storm
Gordon (figure 2) passed well south of Florida Bay causing
northeast and then south southeast winds that may have helped
to flush material out of the bay and into the Gulf of Mexico.
Hopefully this wind field information will assist circulation
modelers to determine how the bay responds to hurricanes.
Numerical simulations of seasonal weather regimes have also begun.
The ARPS model has been configured with a horizontal grid
mesh of 9 km to include the Florida peninsula and surrounding
waters, and 42 hyperbolic tangentially stretched vertical
levels (50 meter vertical spacing in lowest 500 meters) to
resolve the planetary boundary layer. A clay-loam soil
with grass/shrub vegetation is used over land in the two
soil-layer force/restore surface energy budget. ARPS was
then initialized with a homogeneous base state from a morning
August Miami sounding. The horizontal motion fields, depicted by
flow streamlines at the Earth's surface (Figure 3) show that, at 1 PM local time
(elapsed simulation time = 5 hours), the surface heating (temperatures
in the low-mid 90's F) induces a fairly strong sea breeze (SB) front.
There is also a classic cold imprint from Lake Okeechobee -
a divergent surface outflow toward the west. Full solenoidal
circulations develop at both coasts, and a very intense
convective "cell" explodes along the SB front further north.
The realism of the atmospheric simulations will be improved
by initializing the model with non-homogeneous 3-D fields from
the operational National Weather Service Eta/Meso model,
incorporating rain/ice microphysics packages, and using
high-resolution land cover/use, soil/vegetation databases
from the South Florida Water Management District (SFWMD).
Key reference:
South Florida Atmospheric Modeling Workshop (NOAA, Nov. 1994)
Droegemeier, K.K., M. Xue, P.V. Reid, J. Brandley and R. Lindsay, 1991: Development of the
CAPS Advanced Regional Prediction System (ARPS): An adaptive, massively parallel, multi-scale prediction model, Ninth Conference on Numerical Weather Prediction, Denver, Co., American Meteorological Society, Boston, 289-292.
Lord, S. J., and J. L. Franklin, 1987: The environment of Hurricane Debby. Part I:
Winds. Mon. Wea. Rev., 119, 2760-2780.
Ooyama, K. V., 1987: Scale controlled objective analysis. Mon. Wea. Rev.,
115, 2479-2506.
Powell, M.D., S. H. Houston, and T. Reinhold, 1995: Hurricane Andrew's
landfall in
South Florida: Part I: Standardizing measurements for documentation of surface wind
fields. Accepted, Weather and Forecasting.
Powell, M. D., and S. Houston, 1995: Hurricane Andrew's Landfall in South
Florida.
Part II: Surface Wind Fields and Potential Real-time Applications. Accepted, Weather
and Forecasting.
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