UPWELLING IN BROAD FJORDS

A broad fjord is defined here as a stratified fjord whose width exceeds the first baroclinic radius defined from the stratification. When a longitudinal wind blows along such a fjord, the response entails upwelling on one side and downwelling on the other. The physics are identical to those of the classical theory of coastal upwelling, except that here upwelling and downwelling are simultaneously present and interfere with each other. Our solution is based on the impulse method suggested by CSANADY (1977, Journal of Geophysical research, 82, 397-419) and assumes a two-layer stratification. Limiting cases of infinite lower-layer depth (toward one layer) and/or infinitely wide fjord (toward one coast) are explored to appreciate the dependency of the solution on the parameters it involves. The general conclusion is that the shallower and the narrower the fjord, the weaker the upwelling-downwelling response. However, when the wind impulse is large, this is true only for upwelling. Relevance to Porsangerfjord in northern Norway and comparison with a numerical model demonstrate the applicability of the model to observed events.