The number of traveling wave families in a running water with Coriolis force

TL;DR

This paper investigates how Coriolis force affects the number of traveling wave families near shear flows, revealing conditions under which this number changes abruptly, indicating more complex long-term dynamics compared to non-rotating water flows.

Contribution

It establishes the conditions under which the number of traveling wave families changes from finite to infinite in rotating water flows, including for specific shear flows like the sinus profile.

Findings

Number of traveling wave families can change abruptly at a critical beta value.

Flows without critical points maintain a finite number of wave families.

Rotation introduces richer long-term dynamics compared to non-rotating flows.

Abstract

In this paper, we study the number of traveling wave families near a shear flow under the influence of Coriolis force, where the traveling speeds lie outside the range of the flow $u$. Under the $\beta$-plane approximation, if the flow $u$ has a critical point at which $u$ attains its minimal (resp. maximal) value, then a unique transitional $\beta$ value exists in the positive (resp. negative) half-line such that the number of traveling wave families near the shear flow changes suddenly from finite to infinite when $\beta$ passes through it. On the other hand, if $u$ has no such critical points, then the number is always finite for positive (resp. negative) $\beta$ values. This is true for general shear flows under mildly technical assumptions, and for a large class of shear flows including a cosine jet $u(y) = {1+\cos(\pi y)\over 2}$ (i.e. the sinus profile) and analytic monotone flows unconditionally. The sudden change of the number of traveling wave families indicates that long time dynamics around the shear flow is much richer than the non-rotating case, where no such traveling wave families exist.