57A072
Ice drift in the Baltic Sea and Sea of Okhotsk
Annu Oikkonen, Matti Leppäranta, Kunio Shirasawa
Corresponding author: Annu Oikkonen –
annu.oikkonen@helsinki.fi
In this study the ice drift in two very different
regional ice zones is compared. The study is based on the ice-drift observations
made with drifting ice buoys in the Sea of Okhotsk during the winters of 2004
and 2005 and with the ship moored into the drifting ice floe in the Baltic Sea
in March 2009. Ice drift was compared with wind observations in both sea areas.
In addition, in the Sea of Okhotsk sea-level measurements and the tidal
component of sea-level variations were used to study the importance of tidal
forcing. During the Baltic Sea ice-drift experiment, data collected in three
drifting ice stations represented three very different drifting conditions. At
the first ice station (S1) the wind was mild and the icefield was very compact
resulting in very slow drift. In the second ice station (S2) stronger wind
caused faster drift, but also a lot of ice deformations. Fastest ice drift (22
cm s–1) was observed in the
third ice station (S3), where ice drift was very close to free drift. In S1 and
S3 power spectrums of wind and ice drift correspond well over the whole
frequency span, while in S2 correspondence especially in higher frequencies is
clearly weaker and high rates of deformations lower the power of ice drift. In
the Sea of Okhotsk ice was drifting generally much faster than in the Baltic
Sea. Although all of the ice-drift power spectrums do not show very clear tidal
peaks, cross wavelet and wavelet coherence analyses show the importance of
tides. In the cross wavelet transforms of ice drift and sea-level variations
there is significant common power in tidal bands of about 12 and 24 hours, and
the common power varies with varying maximum tide amplitude.
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