Temporal and spatial variability of the internal wave field in a lake with complex morphometry

Javier Vidal, Sally MacIntyre, Erika E. McPhee-Shaw, William J. Shaw and Stephen G. Monismith

Limnol. Oceanogr., 58(5), 2013, 1557-1580 | DOI: 10.4319/lo.2013.58.5.1557

ABSTRACT: To quantify the effect of basin morphometry on internal wave dynamics, we installed thermistor arrays around the perimeter of Mono Lake, California. The lake's complex bathymetry includes alongshore bottom slopes ranging from < 1% up to 9% and a steep-sided peninsula-like island. Under the influence of the dominating winds from the south, isopycnals downwelled along the long axis of the lake as well as along an axis parallel to the peninsula, generating vertical mode 2 horizontal mode 2 internal waves. On relaxation of the wind, a horizontal mode 2 Kelvin wave evolved with a period of ∼ 22 h in each of the two sub-basins. The response of the internal wave field to high winds was spatially variable, with higher vertical excursions of isopycnals and higher rates of strain, indicative of non-linearity and turbulence, at both sides of the peninsula and near steep sloping boundaries to the south. Rate of strain squared was enhanced up to three orders of magnitude relative to background rates depending on bottom slope. Model comparisons in which the island was moved to the center of the lake or removed showed a dominant horizontal mode 1 wave and stronger influence of rotation. Increased complexity of basin morphometry modified the horizontal and vertical phase structure of dominant basin-scale waves, redistributed the potential energy in the internal wave field over space, and shifted the positions of the basins in which the waves rotated. Whether turbulence increased with these shifts depended on the incidence of steep topography.

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