Tides and shallow water dynamics near Tromsø

Abstract

I have investigated the tidal dynamics near Tromsø using data from some observations and from a numerical model. These data show that currents relating to the shallow water tides are very pronounced at the Tromsøysund and Sandnessund constrictions. This is due to two tidal waves - one of them force the northern, while the other force the southern side of those constrictions - being differently influenced by the shallow water tides. The pressure gradient along the channels is therefore significantly influenced by the difference in shallow water tides on either side. Furthermore, the data suggest that high frequency oscillations superimposed on the tidal signal create strong velocities at some stations. The numerical model suggests that these high frequency oscillations can be attributed to dipoles forming at the constrictions. They build up strong low-pressure zones, and propagate downstream after some time. The streamwise momentum balance indicate that dipoles first start moving away from the constriction after making conditions unfavourable for flow-separation close to the constrictions. My results suggest that such dipoles can force a faster flow far downstream of- than at constrictions, and that they do so frequently in Rystraumen.