Earth’s Cryosphere, 2022, Vol. XXVI, No. 5, p. 25-34.

CRYOGENIC PHENOMENA IN SEAS AND OCEANS

FREQUENCY OF OCCURRENCE OF FAST ICE CALCULATED FROM POLYGONS OF DIGITIZED ICE CHARTS USING THE EXAMPLE OF THE KARA SEA

R.I. May^1,2,*, K.R. Ganieva¹, A.G. Topaj³, A.V. Yulin⁴

^{1 St. Petersburg State University, Department of Oceanology, Universitetskaya Emb. 7/9, St. Petersburg, 199034 Russia
2 Krylov State Research Center, Moskovskoe shosse 44, St. Petersburg, 196158 Russia
3 LLC “Bureau Hyperborea”, Kavalergardskaya St. 6A, St. Petersburg, 191015 Russia
4 Arctic and Antarctic Research Institute, Beringа St. 38, St. Petersburg, 199397 Russia
*Corresponding author; e-mail: rimay@mail.ru}

Many elements of the natural environment are areal objects that change their position and shape at all scales of variability. For sea ice, such elements can be fast ice, drifting ice, polynyas, ice massifs, and boundaries of multi-year ice. In other earth sciences, these are the boundaries of glaciers, permafrost, snow cover, forest zone, and various isolines of meteorological and oceanological fields (isotherms, isobars, etc.). To analyze such objects, one can usually use approximations in the form of a grid area (rasterization) or a system of sections. In this article, we suggest a direct analysis of these objects based on operations with vector polygons. An efficient algorithm for calculating the probability (frequency of occurrence) of an unlimited number of polygons has been developed and tested. A criterion for selecting one of the real edges of a polygon as an analogue of the isoline of the probability of intersections of polygons is proposed. The developed method has been tested using data on the fast ice of the Kara Sea taken from the digital ice charts developed by the Arctic and Antarctic Research Institute for 1998–2020. As a result, the charts of fast ice probability for the cold season of each year and for a given time of the year for the entire considered period have been obtained. Based on these data, the operational characteristics of fast ice have been estimated, and a tendency for a decrease in the area of fast ice during the considered period has been revealed. For the beginning of May (the period of the maximum development of fast ice), analogues from factual observations characterizing extreme, median, and quartile probability isolines of fast ice occurrence have been found.

Keywords: fast ice, sea ice, Kara Sea, analysis of polygons

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Recommended citation: May R.I., Ganieva K.R., Topaj A.G., Yulin A.V., 2022. Frequency of occurrence of fast ice calculated from polygons of digitized ice charts using the example of the Kara Sea. Earth’s Cryosphere 26 (5), 25–34.