Experimental study of internal wave generation by convection in water

TL;DR

This experimental study explores how convection in water generates internal waves at the interface between turbulent and stratified layers, providing insights relevant to atmospheric and stellar phenomena.

Contribution

The paper demonstrates that internal waves are passively excited by convection in water and that their propagation aligns with dissipative linear wave theory, using novel laboratory measurements.

Findings

Most convective energy is at low frequency and localized near the interface.

Some energy radiates far from the interface via higher frequency, shorter wavelength waves.

Wave propagation matches dissipative linear wave theory.

Abstract

We experimentally investigate the dynamics of water cooled from below at 0^oC and heated from above. Taking advantage of the unusual property that water's density maximum is at about 4^oC, this set-up allows us to simulate in the laboratory a turbulent convective layer adjacent to a stably stratified layer, which is representative of atmospheric and stellar conditions. High precision temperature and velocity measurements are described, with a special focus on the convectively excited internal waves propagating in the stratified zone. Most of the convective energy is at low frequency, and corresponding waves are localized to the vicinity of the interface. However, we show that some energy radiates far from the interface, carried by shorter horizontal wavelength, higher frequency waves. Our data suggest that the internal wave field is passively excited by the convective fluctuations, and the wave propagation is correctly described by the dissipative linear wave theory.