Vertical propagation of lakewide internal waves

Abstract

Internal waves with diurnal period dominated velocities measured by an Acoustic Doppler Profiler (ADP) in a small lake (main basin 3000 m by 400 m by 18 m). ADP profiles and an along‐lake temperature section indicate that the observed waves, like seiches, had horizontal wavelengths exceeding the metalimnion length. However, unlike non‐dissipative seiches, the observed waves propagated vertically, carrying energy to the lakebed where waves were absorbed, rather than being strongly reflected. This absorption is predicted by a standard parameterization of boundary layer dissipation. The absence of upward‐propagating energy precludes seiche resonance, limits focusing of waves toward attractors, and suggests that hypolimnion dissipation was limited by the supply of downward‐propagating energy. Vertical wavelengths were less than the lake depth. Simplified calculations suggest that vertically‐propagating waves, as opposed to vertically standing seiches, are most likely where vertical wavelengths are short, near‐bed stratification is strong, and lakes are short and deep.