Internal Waves Research Articles

Can β-blockers prevent intracranial aneurysm rupture? - insights from Computational Fluid Dynamics analysis.

Hypertension is a risk factor for intracranial aneurysm rupture. We analyzed whether the intake of drugs from specific classes of anti-hypertensive medications affects hemodynamic parameters of intracranial aneurysm dome. We recorded medical history including medications and the in-hospital blood pressure values. We then obtained 3D reconstruction of each patients' aneurysm dome and the feeding artery. Using OpenFOAM software we performed Computational Fluid Dynamics analysis of blood flow through the modeled structures. Blood was modeled as Newtonian fluid, using the incompressible transient solver. As the inlet boundary condition we used the patient-specific Internal Carotid Artery blood velocity waves obtained with Doppler ultrasound. We calculated haemodynamic parameters of the aneurysm dome. All presented analyses are cross-sectional.We included 72 patients with a total of 91 unruptured intracranial aneurysms. The history of β-blocker intake significantly influenced hemodynamic parameters of aneurysm dome. The patients on β-blockers had significantly smaller aneurysm domes (5.09 ± 2.11 mm vs. 7.41 ± 5.89 mm; p = 0.03) and did not have aneurysms larger than 10 mm (0% vs 17.0%; p = 0.01). In the Computational Fluid Dynamics analysis, walls of aneurysms in patients who took β-blockers were characterized by lower Wall Shear Stress Gradient (1.67 ± 1.85 Pa vs. 4.3 ± 6.06 Pa; p = 0.03), Oscillatory Shear Index (0.03 ± 0.02 vs. 0.07 ± 0.10; p = 0.04) and Surface Vortex Fraction (16.2% ± 5.2% vs. 20.0% ± 6.8%; p<0.01). After controlling for covariates, we demonstrated difference of Surface Vortex Fraction (F[1, 48] = 4.36; p = 0.04) and Oscillatory Shear Index (F[1, 48] = 6.51; p = 0.01) between patients taking and not taking β-blockers, respectively. Intake of β-blockers might contribute to more favorable hemodynamics inside aneurysmal sac. Other antihypertensive medication classes were not associated with differences in intracranial aneurysm parameters.

Characteristics of internal waves within thermohaline staircase region in the Caribbean Sea

Thermohaline staircases play a crucial role in the vertical transport of heat and salt in the thermocline. However, there are few in-situ observations of internal waves within thermohaline staircases. The seismic method offers high horizontal resolution and full ocean depth images over large volumes of the ocean, which can enable the visualization of internal waves within the thermohaline staircase region. In this paper, we characterize and analyze internal waves within thermohaline staircases in the Caribbean Sea using two-dimensional seismic data. Snapshots of fine structure displacements caused by internal waves are captured. We calculate the horizontal wavenumber spectra of the vertical displacement of internal waves, which closely align with the Garrett-Munk tow spectrum, indicating features of background internal wave field. We employed the Empirical Mode Decomposition (EMD) method to analyze vertical displacement data of internal waves derived from seismic data and obtained new results. The internal waves within thermohaline staircases consist of some dominant wavelength components of around 0.34 km, 0.83 km, 1.8 km, 6.25 km, 12.5 km, and 25 km. Wavelengths of approximately 0.34 km, 0.83 km, 1.8 km, and 6.25 km are coupled between the upper and lower sections, indicating the vertical transmission of the energy of high-wavenumber internal waves. By applying the prestack migration method, we observed that internal waves within thermohaline staircases display a staggered pattern. Except for the fractured strip structure, other reflectors show subtle alterations, suggesting that the thermohaline staircase stays stable during the acquisition period. Seismic oceanography emerges as a reliable method for studying internal wave characteristics within thermohaline staircases. It has the capacity to facilitate research on the complex dynamics of the ocean at multiple scales.

Tidal dissipation in evolved low- and intermediate-mass stars

As the observed occurrence for planets or stellar companions orbiting low- and intermediate-mass evolved stars is increasing, so is the importance of understanding and evaluating the strength of their interactions. This is important for the further evolution of both our own Earth-Sun system and most of the observed exoplanetary systems. One of the most fundamental mechanisms behind this interaction is the tidal dissipation in these stars, as it is one of the engines of the orbital and rotational evolution of star-planet and star-star systems. This article builds upon previous works that studied the evolution of the tidal dissipation along the pre-main sequence and the main sequence of low- and intermediate-mass stars and found a strong link between the structural and rotational evolution of stars and tidal dissipation. This article provides, for the first time, a complete picture of tidal dissipation along the entire evolution of low- and intermediate-mass stars, including the advanced phases of evolution. Using stellar evolutionary models, the internal structure of the star was computed from the pre-main sequence all the way up to the white dwarf phase for stars with initial masses between 1 and 4 M$_ Using this internal structure, the tidal dissipation was computed along the entire stellar evolution. Tidal dissipation was separated into two components: the dissipation of the equilibrium (non-wave-like) tide and the dissipation of the dynamical (wave-like) tide. For evolved stars, the dynamical tide is constituted by progressive internal gravity waves. The evolution of the tidal dissipation was investigated for both the equilibrium and dynamical tides, and the results were compared. The significance of both the equilibrium and dynamical tide dissipation becomes apparent within distinct domains of the parameter space. The dissipation of the equilibrium tide is dominant when the star is large or the companion is far from the star. Conversely, the dissipation of the dynamical tide is important when the star is small or the companion is close to the star. The size and location of these domains depend on the masses of both the star and the companion, as well as on the evolutionary phase. Both the equilibrium and the dynamical tides are important in evolved stars, and therefore both need to be taken into account when studying the tidal dissipation in evolved stars and the evolution of the planetary and/or stellar companions orbiting them.

Effect of Rotation on Wave Mixing in Intermediate-mass Stars

Internal gravity waves are likely to cause mixing in stellar interiors. Studies show that the mixing by these waves changes drastically across age and mass. Here, we study the effect of rotation on this wave mixing by considering a 7 M ⊙ model at zero-age main sequence and mid-main sequence. We compare the mixing profiles at a range of rotation rates (1 × 10−5, 2 × 10−5, 3 × 10−5, 4 × 10−5, and 1 × 10−4 rad s−1) and observe that the mixing decreases with decreasing Rossby number. This can be attributed to the effect of rotation on convection, which influences the amplitude with which the waves are excited near the convective–radiative interface.

Numerical investigation of interaction of two internal solitary waves with different initial wave amplitudes

The present study investigates the collision of two internal solitary waves with different initial amplitudes using a multi-domain boundary element method. It calculates and discusses wave profiles, residence time, and phase shifting. Observations reveal that tail waves are induced during the collision process, with the amplitude of the tail wave increasing as the initial amplitude of the internal solitary wave increases. Residence time, defined in terms of the interaction between waves of different initial amplitudes, decreases as wave amplitudes increase, eventually stabilizing at a constant value. Additionally, phase shifting increases with wave amplitude, with the rate of increase slowing down as the wave profile becomes relatively large.

Does Climate Variability Influence Internal Migration Flows in Senegal? An Empirical Analysis

This paper aims to estimate the total effect of climate variability on interregional migration flows in Senegal. We match regional climate data at origin, represented by normalised rainfall and normalised temperatures (maximum and minimum), with regional migration flow data from Senegal’s Agence Nationale de la Statistique et de la Démographie (ANSD) censuses to construct a panel database covering the five-yearly internal migration waves of 1976, 1988, 2001 and 2013. Using a gravity equation model where migration flows are explained by measures of climatic variability at origin, controlled for geographical, socioeconomic and demographic factors traditionally identified in the literature. Our results show that only negative precipitation anomalies at the origin area act as a push factor and accelerate emigration. In the predominantly agricultural regions, rainfall deficits appear, alongside traditional socioeconomic variables, as an additional significant factor shaping mobility across the country.

Early detection of Tonga volcanic-eruption from internal gravity wave effects on ionosphere, using satellite geodetic techniques

The occurrence of some natural hazards in the troposphere may lead to creation of Internal Gravity Waves (IGWs). These waves transfer energy from the lower troposphere to upper layers, and to the ionosphere. When these IGWs reach the ionosphere, they create significant variations in the ionospheric parameters. Therefore, they have considerable effects on performance of Global Navigation Satellite Systems (GNSS) receivers. In this study, we used double-frequency measurements of GNSS ground-based stations from GEONET network in New Zealand to detect the IGWs created by the tsunami induced from the 2022 Tonga volcanic eruption. In addition to GNSS measurements, FORMOSAT-7/COSMIC-2 (F7/C2) data, and SWARM data were also used to study these IGWs. It is known that many of the IGWs have horizontal phase speeds faster than that of the tsunami. As the volcanic-originated IGWs spread in cone-shape pattern, it is possible to detect these fast IGWs in the ionosphere earlier than the tsunami waves, reaching the tide gauges or DART buoys. In our study, we could detect the first IGWs at the New Zealand GNSS stations, 2 h earlier than the first registration of the tsunami waves at tide gauges and DART buoys near the New Zealand peninsula, which is located approximately 1.600 km from the Tonga Volcano. It can be concluded that IGWs can be used to warn tsunamis faster than the current early-warning systems, which make use of tide gauges and DART buoys. Furthermore, the spatial variations in ionospheric electron density (IED) were investigated using F7/C2 RO data. The results show that the volcanic-originated IGWs cause reduction in the IED peak value and altitude. The results of IED derived from F7/C2 and SWARM were in good agreement.

A sequence of weather‐driven hydrodynamic events stimulates the formation of harmful algal blooms on an oligotrophic lake

AbstractHarmful algal blooms (HABs) are common in many eutrophic lakes and frequently associated with nutrient excesses, warm waters, and calm conditions. While HABs can also occur in oligotrophic waterbodies, bloom‐stimulating factors remain elusive for these ecosystems. Here, using a high‐frequency sensor platform supported by hydrodynamic modeling, we document a clearly linked sequence of three hydrodynamic events that immediately preceded each HAB event on Skaneateles Lake, NY during 2018. HABs were first preceded by interactions between internal waves in the thermal structure of the lake with the northern slope of the lakebed. These interactions disturbed sediments resulting in upwelling of nutrient‐rich sediment and possibly cyanobacterial cells into the lower water column. Next, moderate winds stimulated Langmuir circulation which facilitated the transport of material from the lower water column to well‐lit surface waters. Finally, the sequence culminated with a calm wind period, which is often classically associated with surface HAB formation. While individual steps in this sequence occurred independently and repeatedly throughout the year, the complete sequence occurred only eight times, immediately preceding each of the eight documented HABs. We empirically derive thresholds for and timing of the sequence to independently predict HAB occurrence and elevated cyanobacteria levels in the lake. The discovery of this specific and repeated event sequence and the identified thresholds provides the potential for forecasting of HABs days in advance. Ongoing climate change impacts, including increasing water column thermal stratification and changing wind speeds may alter the frequency, timing, and duration of this sequence and consequent HAB formation.

Laser ultrasonic testing of defects in milling groove brazed joints of thrust chamber

This paper presented a new approach for noncontact inspection of defects in milling groove brazed joints of thrust chamber with laser ultrasonic testing method and synthetic aperture focusing technique (SAFT). Firstly, laser ultrasonic testing methods for milling groove brazed joints of thrust chamber was studied. Subsequently, numerical models were constructed to analyze the influence of defects on laser-excited signals. The analysis revealed that the brazed defects caused internal waves to reflect on the rib surface, manifesting as defect echo signals preceding the outer wall echo. Through scanning setting, the obtained SAFT images illustrate the presence of the defect directly and clearly. Furthermore, an experimental system was established to detect and image artificial defects with different degrees of weld leakage. The experimental results are consistent with simulation results, validating the capability and effectiveness of the testing and imaging method. In general, the proposed laser ultrasound method offers inherent advantages of non-contact detection with high resolution and precision, and it is easy to achieve fast and automated scanning of large and complex structures like thrust chambers, demonstrating its potential for enhancing the safety and reliability of liquid rocket engines.

Qualitative difference between large waves in deep and shallow fluid formulations

The note addresses a qualitative difference between shallow (vertically confined) and deep (vertically non-confined) fluid geometries for stationary internal solitary waves. It is shown that in a deep fluid, the propagation velocity of large amplitude wave (with a vortex inside) is greater than the velocity predicted by small but finite amplitude theory, known as the Benjamin-Ono model. This effect has been found both asymptotically and experimentally. For the case of a shallow fluid, the situation is qualitatively different. The speed of a wave with vortex inside is smaller than that predicted by the Korteweg-de Vries theory. The reported observation could distinguish wave motions in shallow (confined) and deep (non-confined) geometries and seems to be important in a variety of applications.

Tuning control parameters of underwater vehicle to minimize the influence of internal solitary waves

ISWs (Internal solitary waves) are waves that occur in stratified oceans, generating strong shear near the pycnocline. Encountering ISWs can cause a vehicle to experience the phenomenon of “falling deep”. Therefore, it is quite necessary to exert control on the vehicle in order to effectively avoid this phenomenon. This study establishes a numerical wave tank for ISWs based on the mKdV (modified Korteweg de Vries) theory. Additionally, a PD (Proportional Derivative) control method is developed for vehicles encountering ISWs in stratified fluids. The PD control parameters are designed and tuned, and the vehicle's control effectiveness, motion response and hydrodynamic characteristics, are analysed. The results suggest that this control method can effectively reduce the heave and pitch motions of the vehicle in different submergence depths and wave amplitudes. The pitch angle can be controlled within 0.2 rad for different control parameters. Better control can suppress changes within a range of 0.1 rad. To better evaluate the control effect, a new evaluation parameter σ is proposed, which takes into account both heave and pitch motions. After implementing control, the value of σmax significantly decreases. Optimal control parameters can reduce the value of σmax by about 90% compared to an uncontrolled vehicle.

The boundary layer instability beneath internal solitary waves and its sensitivity to vortex wakes

We investigated the stability of the bottom boundary layer (BBL) beneath periodic internal solitary waves (ISWs) of depression over a flat bottom through two-dimensional direct numerical simulations. We explored the convective versus absolute/global nature of the BBL instability in response to changes in Reynolds number, and the sensitivity of the instability to seeding noise in the front of the ISW – spanning laboratory to geophysical scales. The BBL was laminar at $Re_{ISW}=90$ and convectively unstable at $Re_{ISW}=300$ . At laboratory-scale $Re_{ISW}=300$ , the convective wave packet was periodically amplified by each successive ISW, until vortex shedding occurred. The associated noise-amplification behaviour potentially explains the discrepancies of the critical $Re_{ISW}$ between the lock–release laboratory experiments and our Dubreil–Jacotin–Long-initialized numerical simulations as the result of the difference in background noise. Instability energy decreased under the front shoulder of the ISW, analogous to flow relaminarization under a favourable pressure gradient. At geophysical-scale $Re_{ISW}=900$ , the BBL was initially convectively unstable, and then the instability tracked with the ISW, appearing phenomenologically similar to a global instability. The simulated initial convective instability at both $Re_{ISW}=300$ and $Re_{ISW}=900$ is in agreement with local linear stability analysis which predicts that the instability group speed is always lower than the ISW celerity. Increased free stream perturbations in front of the ISW and larger $Re_{ISW}$ shift the location of vortex shedding (and enhanced bed shear stress) beneath the wave, closer to the ISW trough, thereby potentially changing the location of maximum sediment resuspension, in agreement with field observations at higher $Re_{ISW}$ .

Influence of temperature-dependent density inhomogeneity on the stability of atmospheric stratified fluids

The stability of atmospheric stratified fluids is revisited to study the influence of the temperature-dependent density inhomogeneity due to thermal expansion in the Earth’s lower atmosphere (with heights 0 to 50 km) under the action of gravity. Previous theory in the literature [Phys. Lett. A 480 (2023) 128 990] is modified and advanced. It is found that the Brunt-Väisälä frequency associated with internal gravity waves is modified, leading to new instability conditions of vertically stratified fluids. The possibility of the onset of Rayleigh-Bénard convective instability is also discussed, and the influences of the modified Brunt-Väisälä frequency and the density and temperature gradients on the instability growth rates are studied.

Seismic oceanography of internal solitary waves offshore the South Island, New Zealand

Seismic oceanography has been widely used in the study of internal solitary waves (ISWs) in recent years, and has achieved remarkable results. In this paper, we analyzed the multi-channel seismic reflection data in the Canterbury Basin offshore New Zealand from January 9 to January 29, 2000, collected by R/V Maurice Ewing. We observed 4 groups of ISWs (labeled ISW1s to ISW4s) on 4 seismic survey lines. We studied their waveforms and propagation speeds in detail. There are two theoretical structures used to describe the vertical waveform of ISWs: the first-order nonlinear vertical structure and the linear vertical structure. We found that ISW1s fit the nonlinear structure well, ISW3s and ISW4s fit the linear structure, and ISW2 does not fit either one. As the water depth increases, the waveforms of all ISWs gradually widen. Two satellite SAR images reveal that all ISWs generally travel shoreward across the isobaths. However, the propagation direction of ISW1s is about 354°-360° (clockwise from due north), different from the propagation directions of other ISWs (about 22°-26°), which explains why ISW1s have the largest characteristic half-height width. The estimated propagation speeds are close to the theoretical speeds, confirming our speed correction method. In the end, we also discuss the interaction of ISWs and eddies.

Hamiltonian shocks

AbstractWave propagation in the form of fronts or kinks, a common occurrence in a wide range of physical phenomena, is studied in the context of models defined by their Hamiltonian structure. Motivated, for dispersive wave evolution equations such as a strongly nonlinear model of two‐layer internal waves in the Boussinesq limit, by the symmetric properties of a class of front‐propagating solutions, known as conjugate states or solibores, a generalized formulation based purely on the dispersionless reduction of a system is introduced, and a class of undercompressive shock solutions, here referred to as “Hamiltonian shocks,” is defined. This analysis determines whether a Hamiltonian shock, representing locally a kink for the parent dispersive equations, will interact with a sufficiently smooth background wave without inducing loss of regularity, which would take the form of a classical dispersive shock for the parent equations. This property is also related to an infinitude of conservation laws, drawing a parallel to the case of completely integrable systems.

Microlocal analysis of internal wave attractors

Internal waves in two-dimensional aquaria can develop singular profiles, called internal wave attractors, in the long time evolution. We review the microlocal analysis of internal wave attractors, connecting the evolution of internal waves with classical dynamical systems on domain boundaries.

Effects of stratification on overshooting and waves atop the convective core of M⊙ main-sequence stars

ABSTRACT As a massive star evolves along the main sequence, its core contracts, leaving behind a stable stratification in helium. We simulate two-dimensional convection in the core at three different stages of evolution of a $5\,\mathrm{ M}_{\odot }$ star, with three different stratifications in helium atop the core. We study the propagation of internal gravity waves in the stably stratified envelope, along with the overshooting length of convective plumes above the convective boundary. We find that the stratification in helium in evolved stars hinders radial motions and effectively shields the radiative envelope against plume penetration. This prevents convective overshooting from being an efficient mixing process in the radiative envelope. In addition, internal gravity waves are less excited in evolved models compared to the zero-age-main-sequence model, and are also more damped in the stratified region above the core. As a result, the wave power is several orders of magnitude lower in mid- and terminal-main-sequence models compared to zero-age-main-sequence stars.

Compressibility effects on Rayleigh-Taylor instability in magnetized strongly coupled dusty plasma

The compressibility effects have been studied on the internal wave modes and Rayleigh-Taylor (R-T) instability in a magnetized strongly coupled dusty plasma (SCDP). A dusty fluid model is constructed considering the effects of weakly coupled electrons/ions and strongly coupled dust grains under the influence of the gravitational field. The effects of the magnetic field and viscoelastic coefficients have been incorporated under the generalized hydrodynamic (GH) fluid description in a quasineutral dusty plasma. The dispersion relation of R-T instability is derived analytically and discussed in the strongly coupled limit. The compressibility effects have appeared in the internal wave modes, significantly modifying the R-T instability criterion and growth rates. The Coulomb coupling parameter and dust magnetosonic speed suppress the growth rate of the R-T instability in a compressible SCDP.

MS-GWaM: A Three-Dimensional Transient Gravity Wave Parametrization for Atmospheric Models

Abstract Parameterizations for internal gravity waves in atmospheric models are traditionally subject to a number of simplifications. Most notably, they rely on both neglecting wave propagation and advection in the horizontal direction (single-column assumption) and an instantaneous balance in the vertical direction (steady-state assumption). While these simplifications are well justified to cover some essential dynamic effects and keep the computational effort small, it has been shown that both mechanisms are potentially significant. In particular, the recently introduced Multiscale Gravity Wave Model (MS-GWaM) successfully applied ray-tracing methods in a novel type of transient but columnar internal gravity wave parameterization (MS-GWaM-1D). We extend this concept to a three-dimensional version of the parameterization (MS-GWaM-3D) to simulate subgrid-scale nonorographic internal gravity waves. The resulting global wave model—implemented into the weather forecast and climate code Icosahedral Nonhydrostatic (ICON)—contains three-dimensional transient propagation with accurate flux calculations, a latitude-dependent background source, and convectively generated waves. MS-GWaM-3D helps reproduce expected temperature and wind patterns in the mesopause region in the climatological zonal mean state and thus proves a viable internal gravity wave (IGW) parameterization. Analyzing the global wave action budget, we find that horizontal wave propagation is as important as vertical wave propagation. The corresponding wave refraction includes previously missing but well-known effects such as wave refraction into the polar jet streams. On a global scale, three-dimensional wave refraction leads to a horizontal flow-dependent redistribution of waves such that the structures of the zonal mean wave drag and consequently the zonal mean winds are modified.

Internal Waves Force Elevated Turbulent Mixing at Barkley Canyon

AbstractSubmarine canyons are hot spots for topography‐internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf‐break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K1) energy is sub‐inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near‐inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near‐inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M2) energy appears focused near critical shelf‐break and canyon floor topography, due to local and remote baroclinic forcing. The high‐frequency internal wave continuum has enhanced near‐bottom energy at both sites (up to 7 × the Garrett‐Munk spectrum), and inferred dissipation rates, ɛ, reaching 10−7 W kg−1 near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are on the slope, and NI0.2 in the canyon. There is also a build‐up of “shoulder” energy (PSh) near the buoyancy frequency, with a power law fit to dissipation of PSh ∼ ɛ0.3 at both sites.