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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 - PowerPoint PPT Presentation
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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– 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
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)
energywavetotalHs
Photo: Rob Johnson
Photo: Graham Oakley
The deployment
• 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
Variance
Solid line Dashed line
Types of decay
Calm Period Large wave event
Box Plot
Large wave events Calm periods
• Indications of non-linear wave-wave interactions• Possible explanation why linear theory fails
Ice breaking by waves
Storm waves have the capability to maintain floe
breaking potential hundreds of kilometres
from the ice edge
Relevance
Looked for a relationship in the Arctic, but had insufficient data to test
Note: axis is reversed
Future wave climate
• Climate Models predict that wave heights should increase everywhere at the sea ice edge
• This will be a negative feedback on extent
Historical period (1989-99) 2090-2100 RCP 8.5 2090-2100 RCP 4.5
Increases are over 1850 to 1870
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
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)
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
Sea ice concentration