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Antony K. Liu, Seelye Martin, and Ronald Kwok

Abstract

This paper demonstrates the use of wavelet transforms in the tracking of sequential ice features in the ERS-1 synthetic aperture radar (SAR) imagery, especially in situations where feature correlation techniques fail to yield reasonable results. Examples include the evolution of the St. Lawrence polynya and summer sea ice change in the Beaufort Sea. For the polynya, the evolution of the region of young ice growth surrounding a polynya can be easily tracked by wavelet analysis due to the large backscatter difference between the young and old ice. Also within the polynya, a 2D fast Fourier transform (FFT) is used to identify the extent of the Langmuir circulation region, which is coincident with the wave-agitated frazil ice growth region, where the sea ice experiences its fastest growth. Therefore, the combination of wavelet and FFT analysis of SAR images provides for the large-scale monitoring of different polynya features. For summer ice, previous work shows that this is the most difficult period for ice trackers due to the lack of features on the sea ice cover. The multiscale wavelet analysis shows that this method delineates the detailed floe shapes during this period, so that between consecutive images, the floe translation and rotation can be estimated.

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An T. Nguyen, Ronald Kwok, and Dimitris Menemenlis

Abstract

A coupled ocean and sea ice model is used to investigate dense water (DW) formation in the Chukchi and Bering shelves and the pathways by which this water feeds the upper halocline. Two 1992–2008 data-constrained solutions at 9- and 4-km horizontal grid spacing show that 1) winter sea ice growth results in brine rejection and DW formation; 2) the DW flows primarily down Barrow and Central–Herald Canyons in the form of bottom-trapped, intermittent currents to depths of 50–150 m from the late winter to late summer seasons; and 3) eddies with diameters ~ 30 km carry the cold DW from the shelf break into the Canada Basin interior at depths of 50–150 m. The 4-km data-constrained solution does not show eddy transport across the Chukchi Shelf at shallow depths; instead, advection of DW downstream of polynya regions is driven by a strong (~0.1 m s−1) mean current on the Chukchi Shelf. Upper halocline water (UHW) formation rate was obtained from two methods: one is based on satellite data and on a simple parameterized approach, and the other is computed from the authors’ model solution. The two methods yield 5740 ±1420 km3 yr−1 and 4190–4860 ±1440 km3 yr−1, respectively. These rates imply a halocline replenishment period of 10–21 yr. Passive tracers also show that water with highest density forms in the Gulf of Anadyr and along the eastern Siberian coast immediately north of the Bering Strait. These results provide a coherent picture of the seasonal development of UHW at high spatial and temporal resolutions and serve as a guide for improving understanding of water-mass formation in the western Arctic Ocean.

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