Wave Propagation in Continuous Sea Ice: An Experimental Perspective

Abstract

Ocean waves penetrate hundreds of kilometres into the ice-covered ocean. Waves fracture the level ice into small floes, herd floes, introduce warm water and overwash the floes, accelerating ice melt and causing collisions, which concurrently erodes the floes and influences the large-scale deformation. Concomitantly, interactions between waves and the sea ice cause wave energy to reduce with distance travelled into the ice cover, attenuating wave driven effects. Here a pilot experiment in the ice tank at Aalto University (Finland) is presented to discuss how the properties of irregular small amplitude (linear) waves change as they propagate through continuous model sea ice. Irregular waves with a JONSWAP spectral shape were mechanically generated with a very low initial wave steepness to avoid ice break up and maintain a consistent continuous ice cover throughout the experiments. Observations show an exponential attenuation of wave energy with distance. High frequency components attenuated more rapidly than the low frequency counterparts, in agreement with a frequency-cubed power-law. The more effective attenuation in the high frequency range induced a substantial downshift of the spectral peak, stretching the dominant wave component as it propagates in ice.

A New Model Ice for Wave-Ice Interaction

“…The non-linearity is reduced from nearly 70% to 30% for MIVET, while the difference in damping between the conventional model ice and MIVET ranges from 0-100% depending on the wave frequency. As observed in earlier experiments with granular conventional model ice (pr = 80% [30]), the damping in conventional model ice is high and it also acts as a low pass filter as in S1000 where angular wave frequencies above 6 rad/s are filtered out. Some damping in MIVET is present, but it is less pronounced and it remains to be investigated whether the remaining damping refers to the present non-linearity or the wave-ice interface which is identical for S1000 and S2000.…”

“…A series of wave-ice experiments in model ice was presented in Passerotti et al [30], where the stiffness respectively the elastic modulus of the waves were around one to two orders of magnitude below target with a significant non-linearity of the model ice being around pr = 80%. The encountered wave damping was significant resulting in damping of around 50% after five wave-length.…”

“…However, it appears established that wave scattering processes lead to an increased wave attenuation in broken ice fields such as the MIZ [31,32], compared to solid level ice. Therefore, the strong attenuation observed in level ice model tests [30] that appears comparable to that in the MIZ [32] is considered a scale effect. This is likely to be triggered by the inherent plasticity or therewith associated properties of the model ice [27].…”

Laboratory Investigations of the Bending Rheology of Floating Saline Ice and Physical Mechanisms of Wave Damping in the HSVA Hamburg Ship Model Basin Ice Tank

“…Experiments on waves propagation below continuous solid ice were performed in the Large Ice Model Basin (LIMB) of HSVA (Germany) [68][69][70] and in the ice tank at Aalto University (Finland) [71]. In both HSVA experiments, dispersion equations were reconstructed using the records of ice surface elevation.…”