Statistical results of the numerical model of sea ice drift extremes in the south-western part of the Kara Sea

Abstract

The aim of the study was to identify the basic characteristics of ice drift in the south-western Kara Sea and to estimate the extreme drift speed of given probability, including its spatial variability and statistical correlation with the main drift-forming factors. In order to obtain the ice drift data, the numerical dynamic-thermodynamic model of ice cover evolution developed in AARI was used. Its basic specific feature is imitation of ice cover with the help of so-called markers (conventional ice floes). Using three variants of the model grid net (25, 12.5 and 5 km), the ice conditions in the Baidara Bay and the adjoining area in January-March 2018 were simulated. The analysis of the simulation results showed that the average ice drift (average ice transport) is directed from the Baidara Bay to the open sea, i.e. northward with slight deviations mostly to the west. A less detailed grid net results in a smoothed ice drift field, while an increase in the spatial resolution of the model increases the spatial contrasts of the ice drift. The maximum values of the extreme ice drift velocity expressed as “once per N years” occur in the northern part of the model area at the directions of the north-western quarter (up to 1.5-1.8 m/s “once per 10 years” - “once per 100 years”, respectively). The frequency of ice drift velocity exceeding 0.3 m/s is about 4-7 %, and that of ice drift velocity exceeding 0.6 m/s is not more than 1 %. At low drift velocity, the role of inertia is very high, but as the drift rate grows, the inertia contribution decreases noticeably. At increasing drift velocity, the statistical correlation between the ice drift (on the one hand) and the wind, current and sea level tilt (on the other hand) becomes evident. This effect is especially evident for the correlation “drift / wind”. The correlation “drift / ice pressure” depends on the drift speed more or less noticeably at low and high drift speeds, when unidirectional changes of the ice drift and ice pressure happen more often than the opposite ones. At the drift velocities within 0.15-0.60 m\s, the correlation between the ice drift and ice pressure is insignificant, i.e. the unidirectional and opposite changes of the ice drift and ice pressure are almost equally likely.