ИСТИНА

It is dependable grounded that polar ice cap has being shrunk in recent 20-30 years significantly. This manifests among other things in ice-free period duration extension at the Arctic coasts. Ice-free period duration, in turn, is crucial for marine and coastal environment and development, including coastal dynamics as far as it determines coastal bluff exposition to waves and, hence, the intensity of mechanical destruction of coast by waves. If speaking about the Arctic coasts development, ice-free period is crucial for navigation period duration and as far as it is getting longer some management decisions may follow. In this work the OSI SAF sea ice concentration data product of Norwegian and Danish meteorological Institutes (EUMETSAT, 2014) is applied for ice-free period duration assessment in Barents and Kara Seas coasts (Baydaratskaya Bay, Pechora Sea, Dvinskaya Bay). It has daily temporal and 12.5 km spatial resolution and the coverage of 1979 – 2016 period. It is the only product among others with the relatively high resolution and long period covered. The difficulty of satellite data usage in coastal zones is great data contamination by the land surface signal. Due to that contamination sea ice concentration data in 2-3-pixel zone along the coast never reaches 0 or 100% and it really makes IFD detection complicated and uncertain. Still, here we show that OSI SAF-derived IFD has mean accuracy of about 7-12 days (about 10-15% of mean IFD) which is quite high, but enough to describe interannual variability and long-term tendencies, as far as long-term trend is characterized by about 20-50 days (30-100% if compared to the mean value of the 1980s, and 300-600% for the Franz-Josef land) per 35 years. The IFP start and end dates were detected by the original analyses of sea ice concentration annual evolution curve in the nearest to the observation station OSI SAF net cell. 15 sites in the Barents and Kara Seas (including Marresalya and Varandey, where observation data are available). The method is based on the derivative analyses. Validation was made using the variety of alternating sources, namely: observation and reanalyses (CFSR) data, MODIS images, AARI ice charts and free-access reports of local hydrometeorological services about the navigation situation.