Some kinetic energy spectra in a nearshore region of Lake Ontario

Abstract

Data from a recording current meter operated for 104 days in Lake Ontario were augmented with 3 hours of temperature-compensated hot-film anemometer data to develop the kinetic energy spectra for a frequency range of 6.0–1.0 × 10−7 Hz. The measurements were taken approximately 1 km offshore in 9 meters of water, the instruments being located 5.3 meters from the surface. Three hours of hot-film anemometer readings were also collected well offshore in the epilimnion at a depth of 5.8 meters below the surface in 22 meters of water during similar wind climates and sea states. All data were processed by a fast Fourier transform by using ensemble averaging. It was found that the spectrum in the nearshore region was different from that in the offshore region. The nearshore spectrum approximated a slope of −3.0, the energy-containing wave number being 5.3 × 10−3 cm−1 and the integral scale being 2.4 meters, whereas the offshore spectrum approximated a slope of −1.6, the energy-containing wave number being 1.0 − 10−4 cm−1 and the integral scale being 4.3 meters. The viscous dissipation in the nearshore region was 0.11 cm2/sec3, the energy-containing wave number being 1.0 × 10−4 cm−1. Viscous dissipation in the offshore experiment was 0.09 cm2/sec3, the energy-containing wave number being 3.9 × 10−3 cm−1. Little or no kinetic energy existed at wave numbers greater than 3.0 cm−1.