A comparison between vertical motions measured by ADCP and inferred from temperature data

H. van Haren (1)

1 NIOZ - Royal Netherlands Institute for Sea Research

Combined vertical current (w) and thermistor string data demonstrate that high-frequency internal "wave" trains along a pycnocline in a flat-bottom shelf sea consist for 2 periods of a dominant mode-1 non-linear part, while thereafter mainly of linear [mode-2, quadrupled frequency] waves, to first order. In a simple [linear] heat budget, the use of unfiltered temperature gradient or its time mean changes results by only 10%. The observations also demonstrate that temperature is not always adequate to estimate vertical motions using the linear 1-D heat equation. In shallow seas, tidal-w estimated from temperature data can be an order of magnitude weaker than directly observed w, and thus do not represent free internal waves. In the open ocean, tidal motions represent linear waves and are well described by temperature-inferred w. There however, the internal wave continuum is not well-described: near the buoyancy frequency it is dominated by non-linear waves and near [sub]inertial frequencies by eddies and gyroscopic waves.

Domaines: Océan, Atmosphère

H. van Haren. A comparison between vertical motions measured by ADCP and inferred from temperature data. Ocean Science Discussions, 2008, 5 (1), pp.103-121. ⟨hal-00298493⟩