A bottom mounted ADCP has monitored the ice motion and thickness in Bothnian Bay, Baltic Sea during the entire winter season 2004. The ADCP was deployed at 20 m depth at Falkensgrund well outside the land fast ice zone. The data shows that the ice motion is primarily driven by the wind but with a clear influence of internal ice stresses. The ice stresses become more dominant as the ice grow thicker with increasing number of observations with nearly stationary ice for relatively high wind speeds. A clear dependence of the ice/wind speed ratio to wind shifts is detected with higher ratio in the new wind direction. The effect of strain hardening is also seen in several events as decreasing ice speed, sometimes to zero, in spite of constant wind speed and wind direction. A rough force balance computation gives a compressive ice strength of about 9 × 10~4 N m~(-2), which is much larger than normally used in numerical ice models. The ice thickness data show numerous ice ridges with ice draft well above 1 m passing the instrument. The ridges make up a large portion, 30-50%, of the total ice volume showing that dynamical processes are important for the total ice production in the Bothnian Bay.
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机译：底部安装的ADCP监视了整个2004年冬季整个波罗的海博特尼安湾的冰运动和厚度。ADCP部署在陆地快冰区外的Falkensgrund井深20 m。数据表明，冰运动主要由风驱动，但内部冰应力有明显影响。随着相对于高风速几乎静止的冰观测次数的增加，冰越来越厚，冰应力变得越来越重要。在新的风向中，以更高的比率检测到冰/风速比与风向的明确相关性。尽管风速和风向恒定，但在数个事件中也可以看到应变硬化的作用是使冰速降低，有时降至零。粗略的力平衡计算得出抗冰强度约为9×10〜4 N m〜（-2），比数值冰模型中通常使用的强度要大得多。冰层厚度数据显示，许多冰脊从设备通过后，其吃水深度均远高于1 m。脊占总冰量的很大一部分，占30％至50％，这表明动力过程对于博特尼亚湾的总冰产量至关重要。
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