On the boundary layer arising from fast internal waves dynamics

Abstract

In this paper, we investigate the boundary layer arising from the fast internal waves in the Boussinesq equations with the Brunt-Vais\"al\"a frequency of order $ \mathcal O(1/\varepsilon) $. For the homogeneous-in-height stratification, previous work by \emph{Desjardins, Lannes, Saut, 3(1):153--192, Water Waves, 2021} establishes uniform-in-$\epsilon$ estimates locally in time, with additional constraints on the boundary data initially, which essentially restricts the dynamics in the spatially periodic domain. Removing such constraints, our goal is to investigate the general near-boundary behavior. We observe that the fast internal waves will give rise to large growth of the spatial derivatives in the normal direction of the solutions in the vicinity of the boundary. To capture this phenomenon, we introduce an inviscid boundary layer using a natural scaling. In addition, we investigate the well-posedness of such a boundary layer system in the space of analytic functions.