We have examined the development of the Terra Nova Bay polynya (TNBP) using a two-month sequence of Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature (IST) images, complemented by a set of synthetic aperture radar (SAR) images. Results of a comparison between the clear-sky ISTs and the contemporaneous SAR images revealed that the polynya is characterized in the ISTs by a warm core and in the SARs by a bright backscattering area, due to the presence of seawater and grease ice. The activity of the polynya during the period was highly dynamic, with opening and closing phases that had similar temporal length scales, sometimes of less than 24 h. The recent activity of the polynya is evidenced in the SARs by alternate bright and dark backscatter bands formed during openings and calm periods and transported offshore by the ice drift. The thermal fronts that separate the warm core of the polynya from the surrounding ice sheet appeared sharp during the opening phase and smooth during the closing phase. The spatial resolution of 1 km of MODIS ISTs, compared with space-borne passive microwave systems with maximum resolution of approximately 10 km, provides a smaller area for the TNBP than do passive microwave data. The polynya area was detectable up to 80% of time with a revisit time of a few hours, giving an average area of ¡«1300 km2 and peaks up to 3000 km2. The polynya is forced by katabatic winds that have a warm signature, which is also visible in the IST sequence. Katabatic airflows descending from the Reeves Glacier valley contribute to the opening of the polynya in the central part of the bay, while airflows descending from the surrounding glacier valleys contribute to the opening in the north and south of the bay.

The Terra Nova Bay (Antarctica) polynya observed by MODIS ice surface temperature imagery from May to June 2009

BUDILLON, Giorgio
2012

Abstract

We have examined the development of the Terra Nova Bay polynya (TNBP) using a two-month sequence of Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature (IST) images, complemented by a set of synthetic aperture radar (SAR) images. Results of a comparison between the clear-sky ISTs and the contemporaneous SAR images revealed that the polynya is characterized in the ISTs by a warm core and in the SARs by a bright backscattering area, due to the presence of seawater and grease ice. The activity of the polynya during the period was highly dynamic, with opening and closing phases that had similar temporal length scales, sometimes of less than 24 h. The recent activity of the polynya is evidenced in the SARs by alternate bright and dark backscatter bands formed during openings and calm periods and transported offshore by the ice drift. The thermal fronts that separate the warm core of the polynya from the surrounding ice sheet appeared sharp during the opening phase and smooth during the closing phase. The spatial resolution of 1 km of MODIS ISTs, compared with space-borne passive microwave systems with maximum resolution of approximately 10 km, provides a smaller area for the TNBP than do passive microwave data. The polynya area was detectable up to 80% of time with a revisit time of a few hours, giving an average area of ¡«1300 km2 and peaks up to 3000 km2. The polynya is forced by katabatic winds that have a warm signature, which is also visible in the IST sequence. Katabatic airflows descending from the Reeves Glacier valley contribute to the opening of the polynya in the central part of the bay, while airflows descending from the surrounding glacier valleys contribute to the opening in the north and south of the bay.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11367/19950
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