SEMINAR: OI Seminar Series - Dr Flo Kaempf

Dr Flo Kaempf from UWA School of Environmental Systems Engineering.

Title: Sea breezes force near-inertial waves close to the critical latitude for resonance

Abstract: Inertial oscillations are anti-cyclonic motions at the local inertial frequency and are observed globally in regions with weak frictional damping. Near the latitudes 30 deg south and north the inertial frequency is approximately diurnal. Periodic forcing at these 'critical latitudes', by tides or diurnal variations in wind stress, can cause a resonant response in the currents. New observations from a location near the critical latitude for resonance off South Western Australia (Rottnest Shelf) reveal strong anti-cyclonic circular motions that often exceed the mean Leeuwin current by speeds > 0.3 m/s. The observations were made in a region of particularly low tidal energy, therefore the resonant response of the currents is purely driven by the diurnal sea breeze system. As a result the influence of the wind was observed to depths > 250 m (much larger than then the Ekman depth of ~ 70 m). The sea breeze system in South Western Australia is one of the strongest worldwide, frequently exceeding 15 m/s, and contributes to 35% of all wind patterns annually. Consequently, in the absence of significant tidal mixing, the sea breeze forcing of near-inertial waves in this region is an important candidate for vertical mixing across the pycnocline.