Sketch of a first order seiche at time intervals of 1/8 T1 (ie over 1/2 of its period). Arrows indicate the direction of water movement. Water movement is in the opposite direction during the other half of the wave's period.
This figure can also bee seen as an animation.
Figure 10.4 shows a first order seiche in the Baltic Sea, where such oscillations of water level are usually produced by storms systems travelling across. The storm triggers a free oscillation (seiche) which then continues for several days before it is damped by bottom friction.
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