Low‐Frequency Wave Activity in the Ocean—Ross Ice Shelf—Atmosphere System

Abstract

The main subject of this study is the low‐frequency (with the periods longer than 2 hr) wave processes in the coupled regional system of the Ross Ice Shelf (RIS), the Ross Sea and the atmosphere above them. We investigate possible causal relationships between the wave activity in the three media using a unique set of geophysical instruments: a hydrophone measuring pressure variations on the seafloor, a network of seismometers measuring vertical displacements of the RIS surface, and a Dynasonde system measuring wave characteristics at the ionospheric altitudes. We present an extension of the previously introduced theoretical model of the coupled resonance vibrations of the RIS that quantifies the connection between the ocean tide and the resonance vibrations of the RIS. The ocean tide is confirmed as the most significant source of excitation of the resonances. Analysis of average power spectra in year‐long data sets reveals multiple harmonics of the tide (eight) detected by the RIS seismometers while only three are detected by the seafloor sensor. This may represent a confirmation of the effect of resonance‐related broadband amplification predicted by the model. Several peaks in the spectrum of RIS vibrations have periods different from the periods of nearby tidal constituents and may be associated with broad‐scale resonance RIS vibrations. Resonances may play a role in maintaining the coupled atmosphere‐ocean wave activity. Our results reveal a statistically significant correlation between the spectra of the vertical displacements of the RIS and the spectra of the atmospheric waves.

Atmospheric Wave Radiation by Vibrations of an Ice Shelf

“…The natural frequencies of free vibrations are also the resonance frequencies of the RIS oscillations forced by ocean waves (Zabotin et al, 2023). The normal mode solution in Equations 22-24 is obtained in the stratified fluid approximation, which for low-order modes is superior to the alternative thin-plate approximation (Zabotin et al, 2023).…”

“…ρ 1 and ρ 2 are the mass densities of ice and sea water. Equation 22 follows from Equations 22, 27, and 28 in Godin and Zabotin (2016) and the equation Zabotin et al (2023)] that relates the vertical displacement to pressure perturbation p at z = 0. A natural frequency ω of vibrations is determined from the equation…”

“…Because of the large dimensions of the RIS, the fundamental mode and other low-order modes of its free oscillations have periods of several hours. To interpret observations of unusual persistent atmospheric wave activity in the RIS vicinity as well as seismic observations of long period RIS vibrations, a simple, analytical model of low-order vibrations of the ice shelf and their excitation by the ocean has been developed in Godin and Zabotin (2016) and Zabotin et al (2023). RIS is modeled as a homogeneous rectangular plate of constant thickness over ocean of constant depth with a rigid bottom.…”

“…The hypothesis that the persistent atmospheric wave activity was generated by resonant vibrations of the RIS was shown to explain several key features of the observations, including frequency band, vertical wavelength range, and weak variation of the vertical wavelength with height . A direct experimental confirmation of the relation between vertical displacement of the ice surface with atmospheric waves with periods of 2 hours and longer was recently obtained (Zabotin et al, 2023) by combining radar measurements of the wave characteristics at the ionospheric altitudes using a Dynasonde system installed at the Jang Bogo Station, Antarctica (Kim et al, 2022;Kwon et al, 2018) with the measurements of the RIS vibrations using a network of seismometers (Bromirski et al, 2015;Diez et al, 2016).…”

“…In the context of atmospheric waves, the wavenumber integration approach appears to be especially well suited for numerical simulations of waves due to harmonic sources. In this paper, the approach is applied to modeling atmospheric AGWs that are generated by free vibrations of large ice shelves, the energy of which is concentrated around a set of discrete natural frequencies (Godin & Zabotin, 2016; Holdsworth & Glynn, 1978, 1981; Papathanasiou et al., 2019; Sergienko, 2013; Zabotin et al., 2023). As discussed below, an extension of the acoustic wave number integration method to AGWs requires its significant modifications, which are due to the AGWs having trace speeds that may be comparable to the wind speed, and a qualitative difference between the acoustic dispersion relation and the dispersion equation of long‐period AGWs.…”