A Model Of Arctic Ocean Internal Waves Generated By Under Ice Topography

Author : Madison Smith
Publisher :
ISBN 13 :
Total Pages : 161 pages
Book Rating : 4.:/5 (112 download)

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Download or read book The Role of Waves in the Autumn Arctic Ocean written by Madison Smith and published by . This book was released on 2019 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent decline of sea ice coverage in the Arctic Ocean has resulted in a substantial seasonal wave climate. Waves generated in the open water are attenuated far into the sea ice, but are a defining feature of the marginal ice zone (MIZ). In autumn, waves in the MIZ can be large due to the significant open water area following the minimum ice extent. Waves are expected to affect ice cover development through both kinematic and thermodynamic processes. In this research, I use observations from 2015 in the Beaufort Sea region to improve understanding of key feedbacks between waves and sea ice, and describe implications for autumn ice formation. In the MIZ, where surface waves are often present, much of the ice forms through the 'pancake cycle'. Gradients in wave orbital velocities across the surface cause small ice crystals to be herded into increasingly larger, rounded floes. Modeling the relative motion between ice floes is the basis for describing pancake ice growth, as well as the attenuation of wave energy associated with their motion. Here, existing models for ice motion and growth are evaluated using coincident measurements of waves and pancake sea ice made using shipboard stereo video. The observations are well captured by existing models, and relative velocities of floes are typically small compared to the mean orbital velocities. The models for relative motion of pancake sea ice due to waves can be subsequently used to estimate attenuation of wave energy due to floe motion. Under the conditions observed, estimates of wave energy loss from ice-ocean turbulence are much larger than those from pancake collisions, and can account for most of the observed wave attenuation. In addition to the general trends of sea ice growth in the Arctic in autumn, ice edge advance can be temporarily reversed as a result of upper ocean mixing by wind and waves. Observations during a high wind and wave event demonstrate how heat released from the upper ocean can melt significant amounts of newly formed pancake sea ice. Measurements from drifting buoys and ship-based platforms are used to construct heat and salt budgets, which give a consistent picture of the air-ice-ocean evolution. Following the event, there was less heat remaining in the upper ocean and sea ice formation quickly resumed. The young ice cover formed throughout the autumn significantly changes the way in which momentum is transferred from the wind to the waves, and into the ocean below. Using coincident measurements of sea ice, wind, surface waves, and near-surface turbulence across a range of conditions, I quantify the relationship between new sea ice formation, attenuation of waves, and suppression of near-surface turbulence. Sea ice formation reduces the wind input transfer velocity by attenuating the short waves, which simultaneously suppresses the wave-driven near-surface turbulence. As ice thickens and grows, the ice provides the dominant roughness for wind input. Based on the observations, I suggest parameters for estimating near-surface turbulence in thin pancake and frazil ice, which are ubiquitous in autumn marginal ice zones. The results of this research provide validation and parameterization for a new class of sea ice models that include dynamic and thermodynamic floe processes. Constraining rates of pancake ice growth is important as it occurs at a much faster rate than simple thermodynamic ice growth, and it is believed to be more common in the Arctic Ocean in recent years. Yet, as the timing of the ice-edge advance shifts later into stormier autumn months, waves from storm events may play an increasing role in delaying ice advance. Thus, the coupled wave-ice interactions examined are likely to become increasingly important in determining the state of the autumn Arctic Ocean with the growing wave climate.