Monitoring of ice dynamics using bottom-mounted ADCP in the central Gulf of Finland in 2010

This study is aimed to describe the sea ice dynamics in relation to wind forcing using bottom-track (BT) facility of the ADCP for detecting the presence and movement of the ice. The measurements were performed from 12 January to 27 April 2010 in the central part of the Gulf of Finland 15 km off Kunda (59°42.09 N, 26°24.23 E). A broadband ADCP (307.2 kHz, RD Instruments) was configured to measure BT velocities (i.e. sea surface tracking) with the sampling interval of 10 min (average of 5 pings). The relevant wind data were obtained from meteorological station on the island of Vaindloo, about 15 km to the north from the location of ADCP and from the operational model HIRLAM (first three weeks). The winter of 2009/2010 was a bit colder than average, the major parts of the Gulf of Finland were ice covered and especially in the second half of the winter the ice conditions were very dynamic as well. The detection of the ice cover periods based on analysis of the BT error velocity and velocity values. The rms of the BT error velocity for the ice cover periods were 3–5 times smaller than those for the open water periods. Altogether five periods with ice cover with the duration from 6 to 12 days were determined, which makes approximately 60% of the whole ‘ice season’. The alternation of ice cover at the observation site was in a good accordance with variations of wind over the gulf and was confirmed by the available cloud free MODIS (NASA) satellite images. The ice drift velocity was well correlated with the wind velocity during all ice cover periods as inferred from magnitude of the vector correlation coefficients in the range of 0.87–0.99. The ice to wind speed ratio varied between 0.016 and 0.039 and the mean direction of ice drift was to the right from the wind direction by 3°-19°. The study concludes that the bottom-track option of the ADCP applied for detection of ice cover is a reliable tool for monitoring local ice conditions and could be used more widely in the future research.