13 October 2011 Is the katabatic wind the forcing factor of Terra Nova Bay polynya events?
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Abstract
The dynamics of Terra Nova Bay (TNB) winter polynya events has been investigated by means of Sea-Ice Concentration (SIC) maps derived from the observations of the passive microwave sensor AMSR-E; these maps are produced by the Institute of Environmental Physics of the University of Bremen and made available on a daily basis through its web site. The formation and persistence of TNB polynya are thought to be due to the combined effect of katabatic winds, advecting eastward the new formed ice, and of the Drygalski Ice Tongue which inhibits northward ice drift into TNB. To measure polynya extents, an image window covering the area of TNB, approximately from 74.5 to 75.5°S and from 163 to 167°E, was extracted from the whole Antarctic SIC data set. This image window, 20 x 20 pixel size, i.e. 125 x 125 km, which almost exactly circumscribes the TNB polynya, is used for the computation of polynya area. On the basis of previous studies, it is assumed that a SIC pixel is "open water" when its value goes below 70%; polynya area is then computed by multiplying the number of "open water" pixels by the area of one pixel (39.0625 km2). As katabatic wind, blowing eastward down from the Presley Glacier, is considered the main forcing factor in the opening of the polynya, wind data from AWS Eneide station, located in the vicinity of the Italian Antarctic Base "Mario Zucchelli Station" (74.8°S 164.18°E), were retrieved. Eneide station takes measurements of wind speed and direction and air temperature every hour; wind speed and direction were then composed in one single figure defined as effective wind, i.e. the wind component pushing eastward or at 270°. The correlation between effective wind and polynya extents was analyzed by means of the running correlation coefficient function Ri which can reveal the consistency between the forcing factor of the polynya and its opening. Ri function demonstrates that water areas may correlate either positively or negatively with offshore winds. This main result is analyzed and discussed.
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Flavio Parmiggiani, Flavio Parmiggiani, } "Is the katabatic wind the forcing factor of Terra Nova Bay polynya events?", Proc. SPIE 8175, Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions 2011, 817511 (13 October 2011); doi: 10.1117/12.897387; https://doi.org/10.1117/12.897387
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