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Storm Surges - or - Is that an Ocean in my Basement?

Issues: 1. What is a S torm S urge & 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 - or - Is that an Ocean in my Basement?.

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Storm Surges - or - Is that an Ocean in my Basement?

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  1. Issues: 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- or -Is that an Ocean in my Basement?

  2. 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]

  3. 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

  4. Wind-stress Effect • Water piles up, against coast, to height • i.e. 0.1 to 1 m for PEI or Bay of Fundy.

  5. Inverted-barometer Effect • 1cm sea rise per 1mbar pressure drop • 1cm sea rise per 0.1 kPa pressure drop

  6. 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

  7. Timing is Everything! [Surge at high tide is especially bad]

  8. 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)

  9. Some Statistics • Source: www.es.flinders.edu.au/ ~mattom/ShelfCoast/ notes/chapter04.html

  10. 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 1869 Oct 5]. • http:www.magma.ca/~jdreid/saxby25dec.htm

  11. 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)

  12. Truro with/without Saxby-sized Storm Surge

  13. Amherst

  14. 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.

  15. 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

  16. Reminder: Bangladesh gets hit hard • Source: www.es.flinders.edu.au/ ~mattom/ShelfCoast/ notes/chapter04.html

  17. Bangladesh Storm Surges • Types: A <2m ; B 2-5m ; C >5m • Source: www.es.flinders.edu.au/~mattom/ ShelfCoast/notes/figures/fig4a4.html

  18. Topic #3: Prediction Strategies • Physics: mass is conserved ; f=ma • Mathematics: differential equations for weather/ocean prediction • Computing: approximate these equations on a grid

  19. 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

  20. Nature magazine 2001-Oct-31

  21. Dalhousie Prediction System

  22. www . Phys . Ocean . Dal . Ca / ~josko / exper /

  23. Dalhousie Forecast 2000-jan-22

  24. Topic #4:Current Research on Storm Surges • Automatic prediction systems • Storm surges in a changed climate

  25. Josko Bobanovic PhD 1997 • Created air/ocean model • Model turns weather forecasts into ocean forecasts, with no human interaction • Http :// www . Phys . Ocean . Dal . Ca / ~josko / exper /

  26. Surges in Rising-Ocean Case • Natacha Bernier, PhD student • Sea-level increasing

  27. Climate Change • IPCC report (Thomas Stocker)

  28. Global Temperature Change • IPCC report: • Predict 1C to 5C warming by 2100 • Expansion: 0.2m to 1m

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