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Storm-induced sea ice breakup and the implications for ice extent

Storm-induced sea ice breakup and the implications for ice extent. Alison Kohout, Mike Williams , Sam Dean (NIWA) Mike Meylan , University of Newcastle, Australia. Motivation. Assumed the amplitude of all waves decay exponentially in sea ice

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Storm-induced sea ice breakup and the implications for ice extent

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  1. Storm-induced sea ice breakup and the implications for ice extent Alison Kohout, Mike Williams, Sam Dean (NIWA) Mike Meylan, University of Newcastle, Australia

  2. Motivation • Assumed the amplitude of all waves decay exponentially in sea ice • Based on single site observations of small waves in the Arctic in the late 1970’s and early 1980’s • Didn’t fit opportunistic observations • Desire to understand sea ice changes in both polar regions • Increased desire to forecast sea ice

  3. The Experiment Deploy wave buoys at multiple sites Measure vertical acceleration integrate to get wave height Return FFT of 34 min of measurements every 3 hours Buoys last up to 6 weeks Analysis focuses on significant wave height (HS)

  4. The deployment Photo: Rob Johnson • All ice was first year ice (mean thickness: 0.75 m) • All deployed on similar sized ice floes • Floe size in the Marginal Ice Zone increased with distance from the ice edge Photo: Graham Oakley

  5. Variance Solid line Dashed line

  6. Types of decay Calm Period Large wave event

  7. Box Plot

  8. Large wave events Calm periods • Indications of non-linear wave-wave interactions • Possible explanation why linear theory fails

  9. Ice breaking by waves Storm waves have the capability to maintain floe breaking potential hundreds of kilometres from the ice edge

  10. Relevance Note: axis is reversed Looked for a relationship in the Arctic, but had insufficient data to test

  11. Future wave climate 2090-2100 RCP 8.5 2090-2100 RCP 4.5 Historical period (1989-99) Increases are over 1850 to 1870 • Climate Models predict that wave heights should increase everywhere at the sea ice edge • This will be a negative feedback on extent

  12. Summary New waves-in-ice data capturing both calm and storm events Storm waves decay differently to small waves, can no longer assume all waves decay exponentially Predicts energy from waves propagates further Storm generated waves play a larger role in the breakup of sea ice than previously thought Significant wave height increases predicted in both Antarctic and Arctic, this may enhance sea ice retreat

  13. Future work: • Minimize averaging and study each variable in deeper detail • Planning for another voyage in 2016 • Deploying next generation of buoys with the plan to allow routine deployment • Explore potential of extra sensors for both sea ice and other applications • Implementation of wave processes in sea ice models • Thanks to: • Captain and crew of the Aurora Australis • INPROD: Bill Penrose & Scott Penrose • Takenobu Toyota, Martin Doble, Vernon Squire • ACECRC • Australian Antarctic Division • Marsden Fund • Foundation for Research, Science and Technology (FRST)

  14. Sea ice concentration

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