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Summary of Working Paper No. 45-1996

I.3.1: Variability Analysis of Natural Conditions and Influence on NSR Sailing

By Sylvi Vefsnmo and Stig Magnar Løvås, SINTEF Civil and Environmental Engeneering, Trondheim, Norway

The purpose of the study has been to analyse physical environment parameters affecting transit sailing. Regional analysis as well as analysis along sailing routes are given priority. The AARI Sea Ice Charts covering the period 1967-90 have been derived from the World Data Centre for Glaciology at the National Snow and Ice Data Centre and implemented into INSROP GIS and analysed. Variability analyses are carried out for parameters such as total ice concentration, ice thickness, fraction of old ice and presence of fast ice on a monthly basis.

The representativeness of short time series analyses has been studied, by comparing the analyses of daily SSM/I ice data for the period 1987-90 with the analyses of the AARI Sea Ice Chart Database. In the winter months November-April both the AARI and SSM/I analyses show very dense drifting ice both in the Laptev and East-Siberian Seas. In both the Kara Sea and the Chukchi Sea the SSM/I data show lower ice concentrations than the AARI data. The greatest seasonal fluctuations occur at the east and west ends of the route and a short time period will not be representative for regions with large fluctuations. 1990 was a year with especially light ice conditions and this will heavily influence the variability analysis for a short time period. In the Laptev and East-Siberian Seas where the fluctuations are small in winter, the variability analysis will not be very sensitive for the length of the time series.

A methodology to analyse the distribution of different ice conditions along specified routes have been developed and implemented into INSROP GIS. As a demonstration example two sailing routes have been chosen, one representing the coastal transit route and the other representing a northern transit route. Most of the northern transit route passes through very dense drifting ice, only 10-40 % passes through open waters during the summer months June-November. About 30-50 % of the route experience old ice which is dominating in late summer. The most dominating ice conditions are very thick first-year ice. Only 20 % of the route are in thin ice (less than 70 cm). Very dense drifting ice is also dominating along the coastal transit route. The amount of open water increases from May to September where about 60 % of the route goes through open water. In the winter months 30 % of the route goes through fast ice. About 30 % of the route is in old ice during the whole year, except in late summer when the fraction is 50 %. In the summer months about 60-80 % of the route goes through thin ice. During the winter months there is multi-year ice present over 10-20 % of the route.

Ship accident data reported in different INSROP reports have been compiled and compared to the variability analysis of the AARI Sea Ice Charts Database. In the Arctic seas about 40 % of the damages occur in the Kara Sea where the intensity of sailing is highest. About 20 % of the accidents occur in the Laptev Sea and the East Siberian Sea while only about 14 % occur in the Chukchi Sea. The data also show that most of the accidents occur at the end of the navigation period (August-September), where the statistical analysis of the AARI Sea Ice Charts Database shows a high fraction of open water simultaneously with the presence of old ice, which represents obstacles to the ship traffic. The ice accidents are closely related to the ice conditions and the analysis shows that more than 50 % of the accidents are connected to unfavourable ice conditions. Especially 1983 was a year with severe ice conditions and high accident rate.