Observations of Internal Gravity Waves by Argo Floats

Abstract

This study examines the global variability of the internal wave field near a depth of 1000 m using data from a set of 194 Argo floats equipped with Iridium communications, capable of measuring hourly temperature and pressure during the park phase of their 10-day cycles. These data have been used to estimate vertical isotherm displacements at hourly intervals, yielding a global measure of the heaving due to internal gravity waves. The displacement results have been employed to examine the global variability of these waves and how the displacement power spectrum compares to the canonical Garrett–Munk spectrum. Using the data, the authors find correlations between internal wave intensity and seafloor roughness, proximity to the seafloor, and the magnitude of the local barotropic velocity. The measurements also show large seamount-trapped waves at high latitudes and coastally trapped subinertial waves. These observations provide a rough global census of the nature of these waves that can ultimately be used in studies of ocean mixing.

Internal Waves in the East Australian Current

“…Internal tide energy is significantly more nonstationary than typical in the deep ocean, suggesting refraction by the strong and variable currents of the EAC. The data fill an important geographical gap in the maps of Alford (2003a), Alford and Zhao (2007a), Simmons and Alford (2012), and Hennon et al (2014) and support the general notion that low-mode near-inertial and internal-tide fluxes can travel far from their sources, still with unknown fates Zhao et al, 2016). Additionally, they provide a description of the internal wave environment in a region that is a complex superposition of many processes, rather than considering specialized cases in isolation.…”

“…Contrary to the long‐held picture of a fairly spatially and temporally constant internal wave spectral level (the “Garrett‐Munk 1976” or GM76 spectrum; Cairns & Williams, ; Garrett & Munk, ), more recent studies using moorings and Argo floats have begun to document significant spatial and temporal variations from the GM76 spectrum (Hennon et al, ; Polzin & Lvov, ; Whalen et al, ), with implications for the resultant mixing as turbulent dissipation often scales as internal wave energy squared (Gregg, ). By documenting these continuum levels for the first time in a new region, these observations fill an important gap in those studies.…”

“…Model fluxes in the inset are on the same scale as observed values. The dominant internal wave sources in the model are the Solomon Islands (9.5 ∘ S, 160 ∘ E) and the two ridges at upper right, which are to the east of New Caledonia (just off the plot at 21 ∘ S, 164 ∘ E.) studies using moorings and Argo floats have begun to document significant spatial and temporal variations from the GM76 spectrum (Hennon et al, 2014;Polzin & Lvov, 2011;Whalen et al, 2012), with implications for the resultant mixing as turbulent dissipation often scales as internal wave energy squared (Gregg, 1989). By documenting these continuum levels for the first time in a new region, these observations fill an important gap in those studies.…”

Using CryoSat‐2 altimeter data to evaluate M2 internal tides observed from multisatellite altimetry

“…They have drawn great research interest in recent years, because they play an important role in a wide range of ocean processes such as diapycnal mixing [Munk and Wunsch, 1998;Waterhouse et al, 2014]. Internal tides have been measured using a variety of observational techniques and instruments including moorings [Nash et al, 2012;Kelly et al, 2015], gliders [Johnston et al, , 2015, acoustic tomography [Dushaw et al, 1995[Dushaw et al, , 2009, Argo floats [Hennon et al, 2014], and EM-APEX floats [Terker et al, 2014]. In the past decade, internal tides have been simulated with some degree of success in global high-resolution, eddy-allowing numerical models driven by the astronomical tidal potential and atmospheric forcing [Simmons et al, 2004;Arbic et al, 2010;M€ uller et al, 2012;Shriver et al, 2014].…”

Internal Waves and Mixing near the Kerguelen Plateau

“…There are a few reports presenting observations of several internal wave packets (e.g., Cuypers et al 2013), but no study has yet explored the composition of a regional internal wave field by analyzing the characteristics of dozens of individual internal waves. Instead, previous observations of internal waves have often focused on the spectral characteristics of the internal wave field (e.g., Levine et al 1997;Kunze et al 2002;Fer et al 2010;Dosser et al 2014;Hennon et al 2014;Martini et al 2014). …”