Abstract
Long, non-dispersive coastal wind-generated internal waves in the Hardangerfjord is investigated based on hydrographic data at the coast and current and temperature measurements in the fjord. The aim of the present work is to investigate to what extent coastal wind-generated changes in the pycnocline at the fjord mouth cause the propagation of an internal pulse into the fjord, and the exchange of water in the fjord due to these pulses. A linear two-layer model is applied to describe the dynamics of a stratified, wind-driven coastal area, which is affected by the rotation of Earth, connected to a narrow, channel-shaped fjord where the effect of the rotation of Earth can be neglected. The results from this thesis show that the rapid change in temperature and strong flows measured inside the fjord can be related to along-shore coastal winds, which set up Ekman transports and causes a depression or rise of the pycnocline at the fjord mouth, relative to the wind direction, causing internal pulses that propagates into the fjord. The dynamics described by the two-layer model works best for the coast and outer part of the fjord, where the topography have a channeling shape. From the current measurements, the clearest signal of the pulse is found in the outer part of the fjord, a weaker signal in the middle part of the fjord, and no signal in the inner part of the fjord. These internal pulses are causing an exchange of 40-80 percent of fjord and coastal water in the upper layer of the fjord. It is the period of the internal pulses which controls the volume transport and the exchange of the water in the outer and middle part of the fjord, which again is controlled by the period of the coastal winds