A note on the locus of a shelf front

It is suggested that the locus of a shelf front is where the water depth is equal to the thickness of the tidal frictional bottom boundary layer. From this, it follows that the locus of the front should be given by a critical value of h/U_t, where h is the water depth and U_t is the tidal stream amplitude. This result differs from that suggested by Simpson and Hunter who argued that a critical value of h/U³_t determines the locus of the front. The parameterization suggested here implies that the locus of a shelf front (1) does not adjust in response to the seasonal heating cycle and (2) responds only weakly to the spring-neap cycle. Utilizing established empirical constants, we predict that the locus of a shelf front should be where h/U_t ≅ 80 s. All these predicted features conform well with observed properties of shelf fronts. The bottom boundary layer thickness conformant with these results is equal to λ(C_d-U_t²)^1/2/f, where λ = 0.20 and C_d = 0.003.