Internal seiches

Definition

An internal seiche is a standing wave produced in the interior of a lake at the thermocline level.

When wind blows over a lake, a storm surge is produced that causes the thermocline to tilt in the opposite direction (Figure 1). Once the wind ceases, the thermocline, which forms a sharp interface due to the strong density gradient, begins to oscillate around the nodal point in the center of the lake. This is the point that experiences no vertical motion during a seiche cycle (Figure 1). Maximum amplitudes are observed at the antinodes at the ends of the lake basin. This phenomenon was first interpreted as an internal seiche by Watson (1904).

Internal seiches, Figure 1

Definition sketch for a two-layer approximation of a uninodal internal seiche in a stratified rectangular lake basin. Black dot: nodal point, A: antinodes, dashed line: still water reference level of the thermocline, arrows: mean orientation of water mass movement.