Variability of the internal wave continuum: study of 2500 worldwide seasonal to inter-annual time series

Internal Gravity Waves (IGW) span time scales between the inertial frequency f (∼1 day−1) and buoyancy frequency N (∼15 min−1 in the thermocline). The level of the continuum (defined as all frequencies apart from near-inertial and tidal) is related to small scale mixing, but its energy sources are poorly understood. We hypothesize that the continuum receives energy only from the wind, the tides and the mesoscale turbulence via the generation of near inertial waves (NIW), internal tides (IT) and lee-waves. These then exchange energy with each other and the continuum via triad interactions. If this hypothesis is correct, the kinetic energy (KE) within the continuum should covary with KE of the sources, possibly with a lag. Here, we investigate this relationship within a database of 2500 globally distributed, moored current-meter records (deployed on 697 separate moorings). The time evolution of the KE of the sources and continuum is obtained by computing spectra using sliding 30-days multitaper spectral windows. As a first approximation, the sources are defined as the diurnal and semi-diurnal tidal components and the wind. The preliminary results suggest that, contrary to the conventional view that IGW continuum is constant in space and time, the level varies by a factor of 10 at typical moorings. Additionally, parameters such as the energy level and the correlation between the sources and the continuum are classified and presented as function of geographical position and season.