The Internal Seiches in Gullmar Fjord. Part I: Dynamics

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Abstract
Internal seiche motions with period 1–3 days in Gullmar Fjord are investigated based on mooring data with high vertical and time resolution. The period and structure of the internal seiches are well described by a simple analytical three-layer model taking into account blocking of the basin water at the sill. Energy budgets for forcing and damping of the seiches are estimated. The internal seiches are forced by direct wind stress on the surface and by internal coastal waves of frequency close to the seiches, the latter contribution being a little larger. The e-folding timescale for the internal seiche damping is approximately equal to the seiche periods, which means that the seiches are effectively damped, but also that the forcing must be in near resonance in order to maintain the observed seiche motions. In the basin water the seiches manifest themselves with large vertical motions and clear upward phase propagation. The phase propagation is related with a continuous, rather than strictly layer... Abstract Internal seiche motions with period 1–3 days in Gullmar Fjord are investigated based on mooring data with high vertical and time resolution. The period and structure of the internal seiches are well described by a simple analytical three-layer model taking into account blocking of the basin water at the sill. Energy budgets for forcing and damping of the seiches are estimated. The internal seiches are forced by direct wind stress on the surface and by internal coastal waves of frequency close to the seiches, the latter contribution being a little larger. The e-folding timescale for the internal seiche damping is approximately equal to the seiche periods, which means that the seiches are effectively damped, but also that the forcing must be in near resonance in order to maintain the observed seiche motions. In the basin water the seiches manifest themselves with large vertical motions and clear upward phase propagation. The phase propagation is related with a continuous, rather than strictly layer...

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