Transcript Document 7323079

Storm Surges
- or IsIssues:
that an Ocean in my Basement?
1. What is a Storm Surge & how do they
work?
2. Who cares about SS? (Local & Global)
3. Prediction strategies
4. Current research
http: // www . Phys . Ocean . Dal . Ca /
~kelley / papers / presentations / 2002 /
AST /
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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TOPIC #1:
Q: What is a storm surge?
A: a sea-level rise
(or fall), in excess
of tides.
Caused by
storms...
Wind-stress
Pressure anomaly
[DEMOSTRATION]
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Q: What causes Storm Surges?
Wind stress ... winds sweep water
towards the coast, where it piles up
Inverted-barometer effect... storms are
low-pressure zones, and they suck water
upwards
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Wind-stress Effect
Water piles up, against coast, to height
i.e. 0.1 to 1 m for PEI or Bay of Fundy.
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Inverted-barometer Effect
1cm sea rise per
1mbar pressure drop
1cm sea rise per 0.1
kPa pressure drop
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Geometric Factors
Surges heighten if they flow into a “funnel”
shaped topography
Resonance can occur if geometry is matched
to storm scale and translation speed
Wind-stress is larger for the eastern side of a
low-pressure system moving north (in the
northern hemisphere), so the exact track of
the storm can be important in narrow ocean
domains
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Timing is Everything!
[Surge at high tide is especially
bad]
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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TOPIC #2 ...
Q: Who cares about Storm
Surges?
A: people who live on flat land near coasts.
Local examples:
Bay of Fundy (1869) - Saxby Gale
PEI (2002)
World examples:
Eastern U.S. (rich region)
India and Bangladesh (poor region)
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Some Statistics
Source: www.es.flinders.edu.au/
~mattom/ShelfCoast/ notes/chapter04.html
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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The Saxby Gale: a lunatic idea
Stephen Saxby, 19th century British Naval
instructor
He suggested we can predict storm
surges (tides & weather) based on lunar
cycles
[Modern view: lunar cycles predict tides
only]
Late 1868: Saxby predicted storm
somewhere in world, a year hence [on
“Storm
1869
OctSurges”
5]. Dan Kelley. Oct 2002 AST meeting.
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TO THE EDITOR
... threatens, not only us in Great Britain, but all parts of the earth as
about to happen in the coming year. Some of your readers may
probably be incredulous as to weather warnings given so long an
interval before an expected danger: allow me, therefore, first to give
at least one authentic instance ...
...1869, that at seven a.m., on October 5, the moon will be at that part
of her orbit which is nearest to the earth ... the moon will be on the
earth's equator... and nothing more threatening can, I say, occur
without miracle. ... In the meantime there will be time for the repair of
unsafe sea walls, and for the circulation of this notice by means of
your far-reaching voice, throughout the wide world. Dec. 21 S. M.
SAXBY, R.N.
The Standard; London, England; Friday, December 25,1868; Issue
No. 13,851 Page 5, col. 7 (middle)
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Truro with/without Saxby-sized
Storm Surge
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Amherst
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Moncton Times 1869 Oct 8
... were awakened in the night to find there
dwelling partly filled with water and all means of
reaching dry land apparently cut off ... only
chance of escape seemed to be by means of a
raft ... he and his family got upon it and
committed themselves to the mercy of the
waves ... the raft parted ... The bodies of three
of the children were found on Tuesday but the
other has not yet been recovered.
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Bangladesh
Region is low-lying, densely-populated, and
too poor to erect defences or evacuate.
Surges up to 12-metres can occur.
Example: 1970, a 5-metre surge flooded a
million acres of fields, killing 200,000 people.
Example: few months ago
Predictive models in development by
Physical Oceanographers
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Reminder: Bangladesh gets hit hard
Source: www.es.flinders.edu.au/
~mattom/ShelfCoast/ notes/chapter04.html
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Bangladesh Storm Surges
Types: A <2m ; B 2-5m ; C >5m
Source:
www.es.flinders.edu.au/~mattom/
ShelfCoast/notes/figures/fig4a4.html
“Storm
Surges” Dan Kelley. Oct 2002 AST meeting.
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Topic #3: Prediction Strategies
Physics:
mass is conserved
; f=ma
Mathematics:
differential
equations for
weather/ocean
prediction
“Storm Surges” Dan Kelley.
Computing:
Oct
2002 AST meeting.
approximate
these
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Q: can we predict SS?
A: yes, if we can predict weather
Saxby's error: weather cannot be predicted in
terms of tidal forcing
Prediction involves coupling an atmospheric
model to an ocean model
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Nature magazine 2001-Oct-31
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Dalhousie Prediction System
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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www . Phys .
Ocean . Dal .
Ca / ~josko /
exper /
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Dalhousie Forecast 2000-jan-22
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Topic #4:
Current Research on Storm
Surges
Automatic prediction systems
Storm surges in a changed climate
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Josko
Bobanovic PhD
1997
Created
air/ocean model
Model turns
weather
forecasts into
ocean forecasts,
with no human
interaction
“Storm Surges” Dan Kelley.
Http :// www .
Phys . Ocean .
Dal
Ca /
1
Oct 2002
AST. meeting.
Surges in Rising-Ocean Case
Natacha Bernier, PhD student
Sea-level increasing
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Climate Change
IPCC report (Thomas Stocker)
“Storm Surges” Dan Kelley. Oct 2002 AST meeting.
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Global Temperature Change
IPCC
report:
Predict
1C to 5C
warming
by 2100
“Storm Surges” Dan Kelley.
Expansio
n: 0.2m to1
Oct 2002 AST meeting.