Scaling observations of surface waves in the Beaufort Sea

Madison Smith,Jim Thomson,Jeremy Wilkinson,Jody W Deming

doi:10.12952/journal.elementa.000097

Abstract

Abstract The rapidly changing Arctic sea ice cover affects surface wave growth across all scales. Here, in situ measurements of waves, observed from freely-drifting buoys during the 2014 open water season, are interpreted using open water distances determined from satellite ice products and wind forcing time series measured in situ with the buoys. A significant portion of the wave observations were found to be limited by open water distance (fetch) when the wind duration was sufficient for the conditions to be considered stationary. The scaling of wave energy and frequency with open water distance demonstrated the indirect effects of ice cover on regional wave evolution. Waves in partial ice cover could be similarly categorized as distance-limited by applying the same open water scaling to determine an ‘effective fetch’. The process of local wave generation in ice appeared to be a strong function of the ice concentration, wherein the ice cover severely reduces the effective fetch. The wave field in the Beaufort Sea is thus a function of the sea ice both locally, where wave growth primarily occurs in the open water between floes, and regionally, where the ice edge may provide a more classic fetch limitation. Observations of waves in recent years may be indicative of an emerging trend in the Arctic Ocean, where we will observe increasing wave energy with decreasing sea ice extent.

Highlights

The average summer sea ice extent in the Arctic Ocean has significantly decreased in recent decades
Surface Wave Instrument Floats with Tracking (SWIFTs) 10 was in partial ice cover during the first two weeks of September, and SWIFT 15 was in ice the entirety of its mid-August deployment
Nondimensional wave energy measured in partial ice cover was used to estimate ‘effective’nondimensional distance in ice when winds were off-ice by applying Equation 5. This approach gives the nondimensional ‘effective fetch’ that would place the observations in ice along the same regression line as the observations in open water. (These points are shown as open circles on the black line in Figure 6.) The same screening for duration and distance limitation was applied, and we found no waves in partial ice that qualify as durationlimited due to the short open water distances between floes

Summary

Introduction

The average summer sea ice extent in the Arctic Ocean has significantly decreased in recent decades. The previously perennial Arctic sea ice cover may be entering a seasonal regime comparable to that of the Antarctic (Martin et al, 2014). The increase of wave energy in the partially ice-covered Arctic Ocean, during such storm events, may contribute to the further breakup of sea ice (Kohout et al, 2014). This feedback accelerates the predicted timeline to an ice-free Arctic summer, and motivates study of the dependence of Arctic Ocean surface waves on sea ice coverage

Methods

Results

Discussion

Conclusion