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Exploring Rogue Waves from Observations in South Indian Ocean by Paul C. Liu (NOAA/GLERL, U.S.A.) and Keith R. MacHutcho

Exploring Rogue Waves from Observations in South Indian Ocean by Paul C. Liu (NOAA/GLERL, U.S.A.) and Keith R. MacHutchon (Liebenberg & Stander International, South Africa). What is a rogue wave?. H max /H s > 2. How high can this ratio be?.

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Exploring Rogue Waves from Observations in South Indian Ocean by Paul C. Liu (NOAA/GLERL, U.S.A.) and Keith R. MacHutcho

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  1. Exploring Rogue Waves from Observations in South Indian Ocean by Paul C. Liu (NOAA/GLERL, U.S.A.) and Keith R. MacHutchon (Liebenberg & Stander International, South Africa)

  2. What is a rogue wave? Hmax/Hs > 2 How high can this ratio be?

  3. Western Cape Coast Line of South Africa showing FA Platform location Indian Ocean Atlantic Ocean FA Platform at 38S 22E

  4. Wave Measurement from a Marex Wave Recorder Significant wave height (Hs) Maximum wave height (Hmax) Average zero crossing wave period (Tz)

  5. Wind Speeds Hourly maximums Wind data Hourly averages Wind Direction Temporary Record Hourly averages Time series wave elevations Hm/Hs <2 FA Platform Wind and wave data Significant wave height Hourly ave 1/3 highest Hm/Hs Ratios 2<Hm/Hs < 3 Maximum wave heights Wave data Hm/Hs >2 3<Hm/Hs < 4 Hourly maximums Zero crossing periods Hm/Hs> 4 Hourly averages FA PLATFORM: Wind & Wave Data Structure PRIMARY PROCESSED DATA BY WAVE RECORDER SECONDARY PROCESSED DATA

  6. But that’s not the whole story!

  7. What happen when Hmax/Hs is much larger than 2?

  8. Conventional Rayleigh conditions

  9. Conventional Rayleigh conditions

  10. Comparing the results with some laboratory experiments by Chin Wu of University of Wisconsin Normalize the wave heights with their corresponding zero-crossing wave period, H/gT2

  11. Concluding remarks No. 1

  12. Agulhas Current Medium and long period waves, with lengths from 200m to 1500m, refracted by the Agulhas Bank Short and medium period waves, with lengths from <200m to 500m, refracted by the Agulhas Current Composite wave fronts arising from the deep sea over a long fetch Agulhas Retroflection Short waves, with lengths <200m, passing over the Agulhas bank Schematic Diagram showing a possible mechanism for the combination of wave spectra, leading to the presence of Freak Waves, on the Agulhas Bank

  13. Concluding remarks No. 2

  14. Proposing of a new classification: Typical rogue waves 2.0 < Hmax/Hs < 4.0 Uncommon rogue waves 4.0 < Hmax/Hs

  15. Concluding remarks No. 3

  16. With respect to typical rogue waves, Rayleigh distribution needs revision. With respect to uncommon rogue waves, Rayleigh distribution needs overhaul!

  17. Concluding remarks No. 4

  18. We need more, actual, continuous wave time series measurements in order to substantially verify or refute the existence of these uncommon rogue waves!

  19. Progress in science is sometimes made by great discoveries. But science also advances when we learn that something we believed to be true isn’t. When solving a jigsaw puzzle, the solution can sometimes be stymied by the fact that a wrong piece has been wedged in a key place. -- Richard Muller

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