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Internal Solitary Waves and their interaction with sea ice

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SIPW05 - SIP Follow on: Mathematics of sea ice in the twenty-first century

Oceanic internal waves (IWs) propagate along density interfaces and are ubiquitous in stratified water. Their properties are influenced strongly by the nature and form of the upper and lower bounding surfaces of the containing basin(s) in which they propagate.  As the Arctic Ocean evolves to a seasonally more ice-free state, the IW field will be affected by the change at the surface. The relationship between IW dynamics and ice is important in understanding (i) the general circulation and thermodynamics in the Arctic Ocean and (ii) local mixing processes that supply heat and nutrients from depth into upper layers, especially the photic zone. This, in turn, has important ramifications for sea ice formation processes and the state of local and regional ecosystems.  An experimental study of internal solitary waves (ISWs) propagating in a stably stratified two-layer fluid in which the upper boundary condition changes from open water to ice is presented. Grease, level and nilas ice are considered. The experiments show that the internal wave-induced flow at the surface is capable of transporting sea-ice in the horizontal direction. In the level ice case, the transport speed of, relatively long ice floes, nondimensionalized by the wave speed is linearly dependent on the length of the ice floe nondimensionalized by the wavelength. It will also be shown that bottom roughness associated with different ice types can cause varying degrees of vorticity and small-scale turbulence in the wave-induced boundary layer beneath the ice. Measures of turbulent kinetic energy dissipation under the ice are, shown to be comparable to those at the wave density interface. Moreover, in cases where the ice floe protrudes into the pycnocline, interaction with the ice edge can cause the ISW to break or even be destroyed by the process. The results suggest that interaction between ISWs and sea ice may be an important mechanism for dissipation of ISW energy in the Arctic Ocean. Preliminary results from Particle Tracking Velocimetry measurements of experiments using floating polystyrene discs (with the same density as sea ice ρ = 910kg/m3 ) will also be presented. The motion of these discs is compared to the output of a simple numerical model, in order to quantify how ice moves in response to the near-surface internal wave-induced flow. Acknowledgements This work was funded through the EU Horizon 2020 Research and Innovation Programme Hydralab+ and by the Natural Environment Research Council (NERC) funded ONE Planet Doctoral Training Partnership (grant number [NE/S007512/1]). References Carr M, Sutherland P, Haase A, Evers K-U, Fer I, Jensen A, Kalisch H, Berntsen J, Parau E, Thiem O, Davies PA. Laboratory Experiments on Internal Solitary Waves in Ice-Covered Waters. Geophysical Research Letters 2019, 46(21), 12230-12238.

This talk is part of the Isaac Newton Institute Seminar Series series.

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