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We study local magnetohydrodynamical instabilities of differential rotation in magnetized, stably stratified regions of stars and planets using a Cartesian Boussinesq model. We consider arbitrary latitudes and general shears (with gravity direction misaligned from this by an angle |$\phi$|⁠), to model radial (⁠|$\phi =0$|⁠), latitudinal (⁠|$\phi =\pm 90^\circ$|⁠), and mixed differential rotations, and study both non-diffusive [including magnetorotational instability (MRI) and Solberg–Høiland instability] and diffusive instabilities [including Goldreich–Schubert–Fricke (GSF) and MRI with diffusion]. These instabilities could drive turbulent transport and mixing in radiative regions, including the solar tachocline and the cores of red giant stars, but their dynamics are incompletely understood. We revisit linear axisymmetric instabilities with and without diffusion and analyse their properties in the presence of magnetic fields, including deriving stability criteria and computing growth rates, wave vectors, and energetics, both analytically and numerically. We present a more comprehensive analysis of axisymmetric local instabilities than prior work, exploring arbitrary differential rotations and diffusive processes. The presence of a magnetic field leads to stability criteria depending upon angular velocity rather than angular momentum gradients. We find MRI operates for much weaker differential rotations than the hydrodynamic GSF instability, and that it typically prefers much larger length-scales, while the GSF instability is impeded by realistic strength magnetic fields. We anticipate MRI to be more important for turbulent transport in the solar tachocline than the GSF instability when |$\phi \gt 0$| in the Northern (and vice versa in the Southern) hemisphere, though the latter could operate just below the convection zone when MRI is absent for |$\phi \lt 0$|⁠. [ABSTRACT FROM AUTHOR]

Context. Simulations and observations of the solar atmosphere often reveal the presence of torsional Alfvén waves and vortices with sufficient power to heat the solar corona and accelerate the solar wind. Aims. We challenge the long-held view that low-frequency Alfvén waves are suppressed due to inhomogeneities and steep spatial gradients in the atmosphere. Alfvén waves and vortices in a stratified solar atmosphere are modelled with the aim of calculating and comparing their energy flux for different field line geometries. Methods. We show that the general problem of linear Alfvén wave propagation along field lines of arbitrary geometry can be reduced to a set of Klein–Gordon equations for the perturbations of the magnetic field and velocity. Solutions and corresponding energy fluxes are constructed for three cases with different expansion rates of the field lines in the lower atmosphere. Results. Expansion rates that are associated with cut-off free propagation in the lower atmosphere suppress the perturbation amplitudes and the corresponding energy flux. These include the uniform field model and the thin flux tube model. A counterexample with an intermediate field line expansion rate and non-vanishing cut-offs exhibits consistently large perturbation amplitudes and unrestricted energy flux across the entire frequency spectrum. Conclusions. Field lines with different expansion rates and geometries in the lower atmosphere can significantly alter the amplitudes of the Alfvén waves and vortices and the extent of the energy flux entering the corona. [ABSTRACT FROM AUTHOR]

Context. The new in situ measurements of the Solar Orbiter mission contribute to the knowledge of the suprathermal populations in the solar wind, especially of ions and protons whose characterization, although still in the early phase, seems to suggest a major involvement in the interaction with plasma wave fluctuations. Aims. Recent studies point to the stimulating effect of suprathermal populations on temperature anisotropy instabilities in the case of electrons already being demonstrated in theory and numerical simulations. Here, we investigate anisotropic protons, addressing the electromagnetic ion-cyclotron (EMIC) and the proton firehose (PFH) instabilities. Methods. Suprathermal populations enhance the high-energy tails of the Kappa velocity (or energy) distributions measured in situ, enabling characterization by contrasting to the quasi-thermal population in the low-energy (bi-)Maxwellian core. We use hybrid simulations to investigate the two instabilities (with ions or protons as particles and electrons as fluid) for various configurations relevant to the solar wind and terrestrial magnetosphere. Results. The new simulation results confirm the linear theory and its predictions. In the presence of suprathermal protons, the wave fluctuations reach increased energy density levels for both instabilities and cause faster and/or deeper relaxation of temperature anisotropy. The magnitude of suprathermal effects also depends on each instability's specific (initial) parametric regimes. Conclusions. These results further strengthen the belief that wave-particle interactions govern space plasmas. These provide valuable clues for understanding their dynamics, particularly the involvement of suprathermal particles behind the quasi-stationary non-equilibrium states reported by in situ observations. [ABSTRACT FROM AUTHOR]

Long-term trends and dependences on solar activity were derived for wave disturbances at mesopause altitudes (80−100 km) based on temperature variations obtained by spectral observations of the hydroxyl airglow at the Zvenigorod Science Station, Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, in 2000−2024, as well as by methods of statistical analysis. Their activities were determined by digital frequency filtering in three regions of wave periods, such as 0.7−2.0, 1.4−4.1, and 2.7−8.2 h with maxima at 1, 2, and 4 h. The root-mean-square values of temperature half-differences served as an indicator of wave activity. Both year-round and average seasonal (winter and summer) values were analyzed. According to the study results, the wave activity is characterized by positive trends with their dependence on the frequency band of disturbances (in winter, the trend is greater in the high-frequency band, and in summer, the trend is greater in the low-frequency band). The dependence on solar activity is positive. Its values are greater for the high-frequency band of disturbances, as well as in winter. [ABSTRACT FROM AUTHOR]

A study of cosmic ray modified shock structures is presented for a system of four fluids consisting upon cosmic rays, thermal plasmas, forward and backward propagating self-excited Alfvén waves. A fluid model is employed to study the energy exchange mechanisms for the shock formation where cosmic rays, forward and backward propagating Alfvén waves are taken massless fluids in the comparison of thermal plasmas. This work may help to understand theoretical and observational perspective of the processes involved in supernova environment. [ABSTRACT FROM AUTHOR]

This study presents a state-of-the-art risk evaluation approach, designed for spatiotemporal multivariate environmental dynamic wind-wave systems, being either measured or Monte Carlo (MC) numerically simulated over a representative time-lapse. The main objective of this study has been to benchmark/validate the effectiveness and accuracy of the Gaidai multivariate risk evaluation methodology, using the application to in situ raw windspeeds, along with correlated wave-heights measurements, delivered by North Pacific area of the National Oceanic and Atmospheric Administration (NOAA) ocean buoys. The current study outlines a novel risk evaluation methodology, suitable for environmental dynamic systems, that are either MC numerically modeled, or directly physically measured. The intercorrelations between the wind-wave environmental system's critical/key dimensions and components, along with the high dimensionality of complex environmental systems, are not easily addressed by contemporary classic reliability methods. The objective of this study is to apply a novel reliability/risk evaluation methodology to a combined windspeed and correlated wave-height raw data set, recorded by the NOAA buoys within the North Pacific area, to demonstrate the efficiency of the proposed methodology. By reliability/risk assessment in the current study authors primarily mean probability forecast of certain multivariate hazard event. It is well known that when combined, windspeeds along with correlated wave heights form nonlinear dynamic environmental systems, that are complex, multidimensional, nonstationary, and yet intercorrelated. Global warming is only one of several significant factors that have ongoing impact on ocean windspeeds along with correlated wave heights, and environmental system risk evaluation is essential for marine, naval, and offshore structures, operating within specific in situ offshore areas of interest subject to realistic in situ ocean/sea weather conditions. The main goal of this study had been to benchmark and validate novel multivariate risk analysis methodology, making it possible to extract essential information directly from in situ raw environmental measurements. The methodology presented in this study opens the possibility of efficiently yet accurately assessing global failure/damage and hazard risks for multivariate nonstationary nonlinear environmental sea/ocean wind-wave systems. [ABSTRACT FROM AUTHOR]

Sea states are likely highly complex and variable under tropical cyclone (TC) conditions. Outrunning the inner core TC vortex, swell systems can radiate in different directions with different wavelengths. Jointly using several sources of wave observations, it is demonstrated that directional properties of wave fields induced by a TC can now be very well recovered. Directional wave information extracted from Sentinel‐1 wave mode and CFOSAT SWIM are combined with Sofar Spotter drifters and NDBC buoy network. Specific filtering is applied to deal with respective limitations of these observation systems. High consistency between the different data sources is generally obtained, to provide evolving directional distributions of radiating swell systems during the whole TC life time. TC wave properties can then trace particular events associated to extended fetch effects, quantifying the asymmetrical directional wavelength distributions, as function of the TC main characteristics evolving with time (intensity, size, translation). Plain Language Summary: Strong winds varying at relatively small scale inside tropical cyclones make wave generation processes complex and not properly understood. To improve their performances, wave numerical models can be calibrated using in situ or remote wave data measured inside cyclones. Satellite altimeters can be used to provide wave height data, but wave direction and wavelength satellite observations are still very rare and their quality often hampered by strong winds and heavy rains. Wave buoys provide more reliable data but rarely cross the trajectory of a cyclone. Considering the propagation properties of ocean surface waves, a method is proposed to characterize tropical cyclone induced waves by identifying them far enough from their source, where data are expected to be more accurate and more numerous. Taking advantage of four different platforms (satellites and buoys), it is demonstrated that the properties of waves emitted in almost all directions can now be robustly described during a whole tropical cyclone life cycle. Key Points: The wave rose concept is introduced to describe the wavelength directional distribution of TC induced swells with observations far from TCsDifferent observation networks (buoys and satellites) are found to be consistent and complementary to describe this directional distributionThis directional distribution is characterized during TC Larry life cycle, opening perspectives to improve TC waves parametric models [ABSTRACT FROM AUTHOR]

Motivated by recent observations of rapid (interannual) signals in the geomagnetic data, and by advances in numerical simulations approaching the Earth's outer core conditions, we present a study on the dynamics of hydromagnetic waves evolving over a static base state. Under the assumption of timescales separation between the rapid waves and the slow convection, we linearize the classical magneto-hydrodynamics equations over a steady non-axisymmetric background magnetic field and a zero velocity field. The initial perturbation is a super-rotating pulse of the inner core, which sets the amplitude and length scales of the waves in the system. The initial pulse triggers axisymmetric, outward propagating torsional Alfvén waves, with characteristic thickness scaling with the magnetic Ekman number as EkM1/4. Because the background state is non-axisymmetric, the pulse also triggers non-axisymmetric, quasi-geostrophic (QG) Alfvén waves. As these latter waves propagate outwards, they turn into QG, magneto-Coriolis (QG-MC) waves as the Coriolis force supersedes inertia in the force balance. The period of the initial wave packet is preserved across the shell but the QG-MC wavefront disperses and a westward drift is observed after this transformation. Upon reaching the core surface, the westward drift of the QG-MC waves presents an estimated phase speed of about 1100kmy−1. This analysis confirms the QG-MC nature of the rapid magnetic signals observed in geomagnetic field models near the Equator. [ABSTRACT FROM AUTHOR]

Background: In Venezuela, the predominant vaccines administered are BBIBP-CorV and Gam-COVID-Vac. Despite robust evidence from randomized clinical trials validating the effectiveness of COVID-19 vaccines in mitigating hospitalization and mortality, there is still a lack of post-authorization safety studies conducted within this demographic population. Methods: A prospective observational study from October 5, 2021 to March 31, 2022 encompassed COVID-19 vaccinated and unvaccinated patients from four sentinel hospitals in Venezuela. Patient lethality was predicted using Charlson Comorbidity index. Clinical outcomes were assessed through WHO's COVID-19 Clinical Progression Scale. Results: Out of the 175 patients assessed, 85 (48.6%) were vaccinated. The median Charlson Comorbidity index was 3 points, with no statistically significant differences observed between the groups (p = 0.2). A total of 50 (28.6%) patients died during the study period, with higher proportion of deaths in unvaccinated patients (35.6% vs. 21.2%, p = 0.035). Advanced age (OR = 1.043, 95% CI = 1.015–1.071, p = 0.002) was associated with increased death risk, whereas vaccination against COVID-19 (OR = 0.428, 95% CI = 0.185–0.99, p = 0.047), high oxygen saturation (OR = 0.964, 95% CI = 0.934–0.995, p = 0.024), and enoxaparin administration (OR = 0.292, 95% CI = 0.093–0.917, p = 0.035) were associated with decreased death risk. Conclusion: During the third and fourth waves of the pandemic, COVID-19 vaccination was associated with a 57% reduction in lethality among patients in four public hospitals in Venezuela. Key summary points: Less than half (48.6%) of the patients were vaccinated against SARS-CoV-2. At least one out of four patients died during the study period, mainly in the unvaccinated group. Advanced age was associated with a higher risk of death. Vaccination against COVID-19, high oxygen, and enoxaparin administration were factors associated with a lower risk of death. [ABSTRACT FROM AUTHOR]

The key difficulty faced by 2D models for planet–disc interaction is in appropriately accounting for the impact of the disc's vertical structure on the dynamics. 3D effects are often mimicked via softening of the planet's potential; however, the planet-induced flow and torques often depend strongly on the choice of softening length. We show that for a linear adiabatic flow perturbing a vertically isothermal disc, there is a particular vertical average of the 3D equations of motion that exactly reproduces 2D fluid equations for arbitrary adiabatic index. There is a strong connection here with the Lubow–Pringle 2D mode of the disc. Correspondingly, we find a simple, general prescription for the consistent treatment of planetary potentials embedded within '2D' discs. The flow induced by a low-mass planet involves large-scale excited spiral density waves that transport angular momentum radially away from the planet and 'horseshoe streamlines' within the coorbital region. We derive simple linear equations governing the flow that locally capture both effects faithfully simultaneously. We present an accurate coorbital flow solution allowing for inexpensive future study of corotation torques, and predict the vertical structure of the coorbital flow and horseshoe region width for different values of adiabatic index, as well as the vertical dependence of the initial shock location. We find strong agreement with the flow computed in 3D numerical simulations, and with 3D one-sided Lindblad torque estimates, which are a factor of 2–3 lower than values from previous 2D simulations. [ABSTRACT FROM AUTHOR]

Approximately 75% of the world's and California's shores are rocky. Rocky shores are of biological interest owing to their diverse and productive species assemblages, where waves and currents play a critical role in larval dispersal and recruitment. Surface variability for nearshore (5⪅depth⪅60m) $(5\lessapprox \mathrm{d}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h}\lessapprox 60\hspace*{.5em}\mathrm{m})$ rocky bottoms at intermediate wave scale 1/750

In this article, a regional ocean surface waves dataset from Sentinel‐1 A and B Synthetic Aperture Radar (SAR) satellites has been described. The ocean wave data have been extracted from the Sentinel‐1 level‐2 OCN (ocean) product as provided by the European Space Agency and downloadable for this region from the Copernicus Australasia regional data hub. The source OCN data have been produced by evolving versions of Sentinel‐1 Instrument Processing Facility (IPF). The structure of the source OCN NetCDF files changes over time and presents a challenge in performing long duration, time series analyses, including the examination of potential inconsistencies in OCN wave data, due to employment of different IPF versions over the duration of the satellite missions. Here, the input OCN wave data have been homogenized to a single, easily usable standard format after applying a quality assurance and control procedure that removes various inconsistencies in variables, coordinates, dimensions and land flag, and through the addition of new auxiliary variables. The new format has the desirable properties of being compact in size, consistent in structure, and scalable in temporal and spatial coverage. It is also convenient to use and offers opportunities to perform fast, multi‐year regional processing and analysis for calibration and validation studies and scientific applications. No re‐processing of Sentinel‐1 level‐1 data has been carried out in this work. [ABSTRACT FROM AUTHOR]

Dry low emissions (DLE) systems are well-known to be susceptible to thermoacoustic instabilities. In particular, transverse, spinning modes of high frequency may appear, and lead to severe damage in a matter of seconds. The thermoacoustic response of an engine is usually specific to the combustor geometry, operating conditions and difficult to reproduce at the lab-scale. In this work, details of high frequency dynamics (HFD) observed during the early development phase of a new DLE system are provided, where a multipeaked spectrum was noticed during testing. Beginning with an analysis of the measured pressure spectra from three different concepts, an analytical model of the clockwise and anticlockwise transverse waves was fitted to the experimental data using a nonlinear curve fitting approach to produce a simple yet useful understanding of the phenomena. A flamelet-based large eddy simulation (LES) of the entire combustion system was used to complement this analysis and confirm the mode shapes using dynamic mode decomposition (DMD). Both approaches independently identified a spinning second-order mode as the dominant one in the high frequency regime. The LES indicates the coupling of a distortion of swirl profile with a precessing vortex core as a possible cause for the onset of instability. With regard to modeling sensitivities, it is shown that subgrid scale combustion modeling has a strong impact on predicted amplitudes. Ultimately, a thickened-flame model with a modified efficiency function provided consistent results. [ABSTRACT FROM AUTHOR]

Understanding the wave and current conditions of coral reef ecosystems is essential for maintaining their health, as many reef processes are controlled by these hydrodynamic conditions. In this study, high-frequency measurements of tides, waves, and currents were made using acoustic, electromagnetic, and pressure instruments over a 28-d period on the fore-reef and reef flat of a coral reef atoll in the South China Sea. The research revealed wave transformation, tidal and wave modulation of flow, and wave setup conditions for the first time at this typical atoll. Three large wave processes dominated by gravity waves (GWs) are observed in the fore-reef. The GWs are significantly attenuated on the reef flat, whereas infragravity (IG) waves strengthened. The tidal modulation of GWs and IG waves on the reef flat is significant when the incident wave height exceeded 1 m. In the fore-reef, the modulation of progressive tidal waves and large waves leads to relatively stronger upper-layer currents, and weak near-bottom currents are primarily attributed to the dissipation of tidal wave energy by the rough coral terrain. In calm conditions, flow variations on the reef flat are modulated by tides, thereby allowing seawater flow to pass through the reef flat during spring tides. Conversely, during periods with large waves, tidal modulation of flow on the reef flat is less significant, and the cross-reef flow velocity increases with increasing incident wave height. The occurrence of wave setup on the reef flat enhances cross-reef flow towards the lagoon. The wave setup is positively linearly correlated with the incident wave height. The magnitude of wave setup is associated with the distance between the measurement sites on the fore-reef and reef flat. [ABSTRACT FROM AUTHOR]

The Tropical Cloud Oscillation (TCO) in the Martian atmosphere is a shift of clouds in the northern spring and summer tropical cloud belt between the eastern and western hemispheres on an intra‐seasonal timescale of about 10–40 sols. The TCO is a significant intraseasonal variation and may strongly affect the Martian general circulation, water cycle, and dust cycle. We examine TCOs using multiple data sets with a focus on the clouds observed in Mars Daily Global Maps during Mars Year (MY) 29–35. One or more TCO cycles are observed in each MY and the phenomenon is most prominent during Ls = 135°–185°. Space‐time spectral analysis shows a variety of waves which appear to follow the theoretical dispersion relationships of equatorial waves, such as Kelvin waves, Rossby waves, and Mixed Rossby Gravity waves. The TCO appears to be controlled by zonal wavenumber one traveling waves with Kelvin and Rossby wave characteristics and exhibits a fine‐scale latitudinal structure that requires modeling with sufficient resolution. Issues with current data assimilation products for use in studies of Martian equatorial waves due to this fine‐scale structure are discussed. Plain Language Summary: During martian northern spring and summer, a relatively thick water ice cloud belt is observed in the tropics (approximately 25°S–25°N), which modifies large‐scale circulation, global water transport and the atmospheric dust cycle. We report on a Tropical Cloud Oscillation (TCO) that is a periodic shift in the thickness of this cloud belt between the eastern and western hemispheres on timescales (about 10–40 Mars days) longer than that of weather but shorter than that of seasons. Since the TCO involves changes in clouds and implies changes in circulation, it may also modulate the dust and water cycles. We examine TCOs using image data for Mars Year 29–35 (late 2007 through early 2021). One or more TCO cycles are observed in each Mars Year and the phenomenon is most prominent in late northern summer. A wide variety of atmospheric waves are found during TCOs; however, the most important are equatorial waves traveling eastward and westward with one peak and one trough around the planet. These waves have narrow latitudinal length scales and thus require high resolution numerical models to simulate and properly represent in data assimilation products. Key Points: The Martian tropical cloud belt exhibits eastern—western zonal oscillations that are most prominent in late northern summerTropical Cloud Oscillations are controlled by large‐scale low frequency equatorial Kelvin and Rossby wavesEquatorial wave dynamics may have an important effect on the Martian water and dust cycles [ABSTRACT FROM AUTHOR]

We investigate vortex dynamics in three magnetic regions, viz. Quiet Sun, Weak Plage, and Strong Plage, using realistic three-dimensional simulations from a comprehensive radiation-magnetohydrodynamics (MHD) code, MURaM. We find that the spatial extents and spatial distribution of vortices vary for different set-ups even though the photospheric turbulence responsible for generating vortices has similar profiles for all three regions. We investigate kinetic and magnetic swirling strength and find them consistent with the Alfvén wave propagation. Using a flux tube expansion model and linear MHD wave theory, we find that the deviation in kinetic swirling strength from the theoretically expected value is the highest for the Strong Plage, least for the Weak Plage, and intermediate for the Quiet Sun at chromospheric heights. It suggests that Weak Plage is the most favoured region for chromospheric swirls, though they are of smaller spatial extents than in Quiet Sun. We also conjecture that vortex interactions within a single flux tube in Strong Plage lead to an energy cascade from larger to smaller vortices that further result in much lower values of kinetic swirling strength than other regions. Fourier spectra of horizontal magnetic fields at 1 Mm height also show the steep cascade from large to smaller scales for Strong Plage. These findings indicate the potential of vortex-induced torsional Alfvén waves to travel higher in the atmosphere without damping for weaker magnetic regions such as the Quiet Sun, whereas vortices would result in dissipation and heating due to the vortex interactions in narrow flux tubes for the strongly magnetized regions such as Strong Plage. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are bright extragalactic transients likely produced by magnetars. We study the propagation of FRBs in magnetar winds, assuming that the wind is strongly magnetized and composed of electron-positron pairs. We focused on the regime where the strength parameter of the radio wave, a0, is larger than unity and the wave frequency, ω0, is larger than the Larmor frequency in the background magnetic field, ωL. We show that strong radio waves with a0 > 1 are able to propagate when ω0 > a0ωL, as the plasma current is a linear function of the wave electric field. The dispersion relation is independent of the wave strength parameter when ω0 > a0ωL. Radio waves could instead be damped when ω0 < a0ωL, as a significant fraction of the wave energy is used to compress the plasma and amplify the background magnetic field. Our results suggest that FRBs should be produced at large distances from the magnetar (i.e., R > 1012 cm, where the condition ω0 > a0ωL is satisfied). Alternatively, the structure of the magnetar wind should be strongly modified during a flare to allow for the escape of FRBs produced at radii R < 1012 cm. [ABSTRACT FROM AUTHOR]

Context. Recent observations of decayless transverse oscillations have revealed two branches in the relationship between period and loop length. One is a linear relationship, interpreted as a standing mode, while the other shows almost no correlation and has not yet been interpreted conclusively. Aims. We investigated the undersampling effect on observed periods of decayless oscillations. Methods. We considered oscillating coronal loops that closely follow the observed loop length distribution. Assuming that all oscillations are standing waves, we modelled a signal that represents decayless oscillations where the period is proportional to the loop length and the amplitude and phase are randomly drawn. We generated a downsampled signal from the original signal by considering different sample rates that mimic temporal cadences of telescopes, and analysed the periods for sampled signals using the fast Fourier transform. Results. When the sampling cadence approaches the actual oscillation period, there is a greater tendency to overestimate the periods in short loops. We find the same two branches in the relationship between loop length and period of the sampled signals as those seen in the observations. Conclusions. We find that long periods of decayless oscillations occurring in short loops could be the result of undersampling. [ABSTRACT FROM AUTHOR]

Aims. The study investigates the relevance of the seed particle population in the results of particle acceleration in interplanetary shock waves, when wave–particle interactions are treated self-consistently. Methods. We employed the SOLar Particle Acceleration in Coronal Shocks (SOLPACS) model, which is a proton acceleration simulation in shocks with self-consistent nonlinear wave–particle interactions. We compared a suprathermal monoenergetic injection with a two-component injection, including the suprathermal monoenergetic component and a broad-spectrum energetic component corresponding to the observed background particle spectrum. Energetic particles in the beginning of the simulation could increase the local wave intensities sufficiently to increase the rate of acceleration for injected particles and even reshape the resulting particle energy spectra and spatial distributions. The resulting particle energy spectra, particle spatial distributions, and wave intensity spectra are compared to observations made by Solar Orbiter's instrument suite of the 2021 October 30 energetic storm particle (ESP) event to evaluate the relevance of the seed particle population in the acceleration model. Results. The energetic component of the seed particle population shortens the needed acceleration time for particles and enhances the tail of the spectrum to a level that matches the observations. The highest compared energies (> 1 MeV) match only when an energetic component is included in the seed particle population. The wave intensities and spatial distributions, on the other hand, showed no significant differences with the monoenergetic and two-component injection. While the simulated and observed wave intensities match within five minutes before the shock passing, the simulated wave field is too intense farther out from the shock, probably due to a lack of wave damping and/or decay processes in the simulation, leading to particles being slightly overly trapped to regions closer to the shock. [ABSTRACT FROM AUTHOR]

Context. Kinetic-scale dynamics in weakly collisional space plasmas usually exhibits a self-similar statistics of magnetic field fluctuations. This implies the existence of an invariant probability density function (master curve). Aims. We provide an analytical derivation of the master curve by assuming that perpendicular fluctuations can be modeled through a scale-dependent Langevin equation. Methods. In our model, magnetic field fluctuations are the stochastic variable, and their scale-to-scale evolution is assumed to be a Langevin process. We propose a formal derivation of the master curve describing the statistics of the fluctuations at kinetic scales. The model predictions were tested on independent data samples of the fast solar wind measured near the Sun by Parker Solar Probe and near the Earth by Cluster. Results. The master curve is a generalization of the Kappa distribution with two parameters: One parameter regulates the tails, and the other controls the asymmetry. The model predictions match the spacecraft observations up to 5σ and even beyond in the case of perpendicular magnetic field fluctuations. [ABSTRACT FROM AUTHOR]

Solid organ transplant recipients (SOTR) are at increased risk from COVID-19. Over time, the absolute risk of adverse outcomes after COVID-19 has decreased in both the nonimmunosuppressed/immunocompromised (non-ISC) general population, and amongst SOTR. Using the N3C, we examined the absolute risk of mortality, major adverse renal or cardiac events, and hospitalization after COVID-19 diagnosis amongst non-ISC and SOTR populations over five waves of the pandemic (Wave 1: Ancestral COVID; Wave 2: Alpha; Wave 3: Delta; Wave 4: Omicron; Wave 5: Omicron). Within each wave, we determined the relative risk of each outcome for SOTR versus the non-ISC population based on crude event rates, and then used multivariable cox proportional hazards models and logistic regression to determine the adjusted risk of each outcome based on SOT status. Throughout the pandemic, including during the Omicron wave (Wave 5), SOTR were at greater absolute risk for each outcome than non-ISC patients (p-values all <0.001). The adjusted risk of SOT status for each outcome was relatively stable over time (aHR 1.28-1.61 for mortality; aHR 1.31-1.47 for MACE; aHR 1.72-1.90 for MARCE; aHR 1.75-2.07 for AKI; and aOR 1.53-1.81 for hospitalization). Despite a reduction in the absolute risk of COVID-19 complications, the relative risk for SOTR versus the non-ISC population has not improved. [ABSTRACT FROM AUTHOR]

A global inventory of extractive species mariculture in wave-exposed temperate waters shows that the longline is the technology used in more than 99% of the sites (Part 1 of this review). In this second part, I compare the static (longline at rest), quasi-static (tidal sea surface elevation, steady currents and mainline lifting operation) and dynamic (wind seas and swells) loading and motion of surface, semi-submerged and fully submerged longlines used to grow bivalves and kelp. This review is based on a hundred papers published on the subject mostly after 2010 and on simple analytical models used to illustrate the many compromises that must be made to ensure the survivability of the structure and the survival (retention), growth and quality of the cultured biomass. Surface longlines are unsuitable for fully exposed environments. To mitigate storm energy it is necessary to minimize the volume of surface buoys and submerge the mainline to the maximum depth possible. There is however a limit to minimizing the volume of surface buoys due to the uplifting of the mainline by currents. In the case of kelp, its optimal growing depth is within a few meters from the sea surface. This limitation can be partly circumvented by having the kelp float above the mainline. In the case of bivalves, mainline depth can be tens of meters below the sea surface. This comes with some disadvantages including difficulties in maintaining the delicate buoyancy balance, particularly for fully submerged longlines without legs, and reduced access to the mainline, particularly for fully submerged longlines with legs. Devices that allow autonomous or remote-controlled changes of mainline depth on a daily, occasional (husbandry and harvest operations) or seasonal basis have been tested but are not yet used commercially on longlines. [ABSTRACT FROM AUTHOR]

A theory of large-scale flows of rotating partially ionized space and astrophysical plasma in the approximation of the Hall magnetohydrodynamics is developed. Partially ionized rotating plasma describes large-scale processes in the exoplanetary atmospheres of hot Jupiters, the thermospheric–ionospheric system of planets and the Earth, in the protoplanetary disks, along with many other objects of heliophysics and space physics. The derived equations contain nontrivial terms describing the influence of rotation on the Hall current and ambipolar plasma diffusion in addition to the traditional Coriolis force acting upon momentum of the plasma's center of mass. Linear flows are analyzed in the simplest case when gravity is neglected. The dispersion relations for modified Alfvén waves, rotating fast and slow acoustic waves, along with modified whistler waves, are obtained. The slow acoustic waves represent a new type of flows driven by the Coriolis force. The fast acoustic waves correspond to conventional acoustic waves in the absence of rotation. [ABSTRACT FROM AUTHOR]

The SOL2012-05-17 event is remarkable in that it caused one of two ground-level enhancements (GLE71) in Solar Cycle 24. Despite the efforts spent studying this solar event, some aspects of it remain unclear. This relates to the development of a coronal mass ejection (CME), the history of the shock wave, and the flare. Our measurements reveal the following chain of phenomena. Two successive eruptions occurred within a few minutes. The rate of change of the reconnected magnetic flux shows a series of increases corresponding to the acceleration or deceleration of the erupting structures. The temporal profile of the magnetic-flux change rate is similar to the hard X-ray burst. Each eruption excited a disturbance that, propagating outward, accelerated all structures above it. This led to complex kinematic characteristics of the erupting structures that eventually formed a self-similarly expanding CME. The two disturbances became piston shocks and merged into a single, stronger shock. There are indications of transformation of the piston shock into a bow shock, but this occurs at distances exceeding ten solar radii. Components of the described picture were observed in a number of events and can serve as a guide for studies of eruptive flares. [ABSTRACT FROM AUTHOR]

Waves play an important role in the heating of solar atmosphere; however, observations of wave propagation and damping from the solar photosphere to corona through chromosphere and transition region are very rare. Recent observations have shown propagation of 3-min slow magnetoacoustic waves (SMAWs) along fan loops from the solar photosphere to corona. In this work, we investigate the role of area divergence and frequencies on the damping of SMAWs propagating from the photosphere to the corona along several fan loops rooted in the sunspot umbra. We study the Fourier power spectra of oscillations along fan loops at each atmospheric height which showed significant enhancements in 1–2, 2.3–3.6, and 4.2–6 min period bands. Amplitude of intensity oscillations in different period bands and heights are extracted after normalizing the filtered light curves with low-frequency background. We find damping of SMAW energy flux propagating along the fan loop 6 with damping lengths |$\approx 170$| and |$\approx 208$| km for 1.5- and 3-min period bands. We also show the decay of total wave energy content with height after incorporating area divergence effect, and present actual damping of SMAWs from photosphere to corona. Actual damping lengths in this case increases to |$\approx 172$| and |$\approx 303$| km for 1.5- and 3-min period bands. All the fan loops show such increase in actual damping lengths, and thus highlight the importance of area divergence effect. Results also show some frequency-dependent damping of SMAW energy fluxes with height where high-frequency waves are damped faster than low-frequency waves. [ABSTRACT FROM AUTHOR]

A semi-planing catamaran is a type of marine craft that benefits from high speed, in conjunction with the its inherent characteristics such as a large deck and high transverse stability. The aspect ratio, length over the beam of a demi-hull, significantly affects the hydrodynamic performance of this vessel. In this study, the effects of the aspect ratio on the hydrodynamic performance of a semi-planing catamaran in calm water and waves are investigated using numerical simulations. The numerical simulation of the AUT-SEM00 model itself is validated by its model test results. The results show that increasing the aspect ratio significantly increases the wetted surface, and that the increase in resistance in calm water is negligible. In addition, increasing the aspect ratio radically reduces the amplitude of vertical acceleration in waves at the center of gravity by up to 85%. Consequently, the seakeeping performance is considerably improved, and the risk to crew and equipment is reduced. [ABSTRACT FROM AUTHOR]

In recent years, there has been an unprecedented increase in interest in the study of radicalisation. To comprehend this phenomenon, numerous political science and sociological perspectives are emphasised to determine social movement conceptualisations. Using British Muslim youth as a case study, the goal of this article is to explore the themes of identity, resistance, racialisation, and mobilisation as antecedents to Islamist radicalisation. In other words, the few young Muslims who have turned to radicalism have done so due to fractures in their gendered sense of status and belonging at the local, national, and international levels. In this article, I conduct a theoretical and conceptual review of five distinct stages of Islamist radicalisation in the context of the United Kingdom, all of which are influenced by local, national, and international concerns. This discussion supports the argument that these waves of radicalism result from identity fragmentation in local communities and worsen as a result of international events. In the British context, the dangers of radicalism are determined by the intersections of local, global, and international events, or at the micro, meso, and macro levels, and these indicate the greatest risks linked to this phenomenon. [ABSTRACT FROM AUTHOR]

The past twenty years have witnessed critical terrorism studies (CTS) become an increasingly influential body of work. In this article, I offer the first sustained effort to chart CTS' development and transformation by positing three successive waves in its evolution. CTS' first wave, I argue, was characterised by agenda-setting efforts to map the prospects of a distinctively critical approach to terrorism research. Second wave literature elaborated on this nascent project's scope, strengthening and broadening its empirical, conceptual, and methodological ambitions. More recent third wave work seeks to problematise the underpinning assumptions and commitments of earlier CTS literature, especially in relation to its engagement with race and colonialism. Mapping CTS' development in this way, I argue, offers three contributions to knowledge. First, it helps historicise CTS research by detailing the academic and wider contexts of its development. Second, it enables engagement with CTS' pluralism, foregrounding the importance of internal disagreements for its past and future trajectories. And, third, it enables new reflection on the political and normative stakes of differing approaches to, and aspirations for, critical terrorism research. [ABSTRACT FROM AUTHOR]

Only around 40% of rivers globally have deltas, but the conditions which inhibit or facilitate river delta formation are not well understood. Many studies have investigated the response of delta development to marine and river conditions. However, few have investigated the limits of such processes beyond which delta formation may be prevented, and none have done so using numerical modeling. This is in part due to ambiguity in the definition of the term "delta," which can make identification difficult in ambiguous cases. Here we propose a systematic method for identifying deltas, based on: accumulation of sediment above the low tide water level; proximity of such deposits to the initial coastline; and the presence of active channels. We run 42 simulations with identical river (1280m3s−1) $(1280\ {\text{m}}^{3}{\text{s}}^{-1})$ and sediment (0.048m3s−1) $(0.048\ {\text{m}}^{3}{\text{s}}^{-1})$ discharges, under combinations of significant wave height and tidal range typical for coasts globally, and determine if/when a delta is formed by this definition. Where deltas do form, we classify four formational regimes—river‐controlled, river/tide‐controlled, wave‐controlled, and wave/tide‐controlled—and discuss the mechanisms of delta development for each regime. Furthermore, we find that, under the discharge conditions considered, delta formation is prevented for combinations of, approximately, significant wave heights of 2.0m $2.0\ \mathrm{m}$ and tidal ranges ≥3.0m ${\ge} 3.0\ \mathrm{m}$. We hypothesize that inhibition of delta formation can be explained as a consequence of sufficient marine‐driven alongshore sediment transport. This is tested by deriving a 1D alongshore sediment diffusion equation, and comparing predictions made using this formula to the cross‐shore integrated sediment volumes of the simulations. Plain Language Summary: River deltas are accumulations of sand and/or silt that form where rivers discharge to the ocean. Not all rivers form deltas, however, and the conditions that allow or prevent delta formation are not well understood. Here, we run a series of computer simulations modeling a river with unchanging discharge of water and sand, discharging into a marine basin featuring varying combinations of waves and tides. We propose an approach to defining precisely when a delta is or is not present, and apply this in order to determine when/if deltas form in our simulations. The results of these simulations are used to identify the limits of wave height and tidal range beyond which delta formation may be prevented under the discharge conditions modeled. These limits are found to exist at, approximately, combinations of wave heights of around 2.0 m and tidal ranges of 3.0 m or more. We also discuss the ways in which the growth of deltas varies under different combinations of waves and tides. Finally, we use a mathematical formula to test the idea that delta formation may be prevented when sediment is driven alongshore away from the river mouth by waves and tides faster than it can accumulate. Key Points: Idealized numerical modeling of river discharge under varied waves and tides suggests limits beyond which delta formation is preventedDistinct mechanisms of delta formation under larger waves and tides than those modeled in previous studies are elucidatedAlongshore diffusion by combined waves and tides is proposed as an explanatory mechanism by which delta formation is inhibited or prevented [ABSTRACT FROM AUTHOR]

Abstract In this article, a regional ocean surface waves dataset from Sentinel‐1 A and B Synthetic Aperture Radar (SAR) satellites has been described. The ocean wave data have been extracted from the Sentinel‐1 level‐2 OCN (ocean) product as provided by the European Space Agency and downloadable for this region from the Copernicus Australasia regional data hub. The source OCN data have been produced by evolving versions of Sentinel‐1 Instrument Processing Facility (IPF). The structure of the source OCN NetCDF files changes over time and presents a challenge in performing long duration, time series analyses, including the examination of potential inconsistencies in OCN wave data, due to employment of different IPF versions over the duration of the satellite missions. Here, the input OCN wave data have been homogenized to a single, easily usable standard format after applying a quality assurance and control procedure that removes various inconsistencies in variables, coordinates, dimensions and land flag, and through the addition of new auxiliary variables. The new format has the desirable properties of being compact in size, consistent in structure, and scalable in temporal and spatial coverage. It is also convenient to use and offers opportunities to perform fast, multi‐year regional processing and analysis for calibration and validation studies and scientific applications. No re‐processing of Sentinel‐1 level‐1 data has been carried out in this work.

The propagation of a pressure wave in a porous medium with a fractured porous zone was numerically investigated. The study used a two-velocity model of a porous medium and a three-velocity model of a fractured porous medium. The problem was examined in a twodimensional formulation, considering cases when a porous medium has a free surface or is unbounded. The fractured porous zone was shown to have either an ellipseor rectangle-shaped boundary. The influence of such inhomogeneities on the propagation of pressure perturbations was analyzed.

This paper focuses on investigating the well-posedness and stabilization of the generalized Rao-Nakra beam equation. The system consists of four wave equations for the longitudinal displacements and the shear angle of the top and bottom layers and one Euler-Bernoulli beam equation for the transversal displacement. First, we prove that the system is well-posed. Second, we show that the analytic stability holds when all the displacements are globally damped through Kelvin-Voigt damping. Third, we establish the case where the damping acts only on the shear angle displacements of the top and bottom layers. In this case, we prove, by using frequency domain arguments combined with the multiplier method, that the energy of the system decays polynomially with a decay rate $ t^{-\frac{1}{2}} $. [ABSTRACT FROM AUTHOR]

Turbulent solar wind is known to be a main driver of the processes inside the magnetosphere, including geomagnetic storms and substorms. Experimental studies of the last decade demonstrate additional ways of interplanetary plasma transport to the magnetosphere, including small-scale processes in the magnetosphere boundary layers. This fact implies that properties of the solar wind turbulence can affect the geomagnetic activity. However, in front of the magnetosphere are a bow shock and a magnetosheath region which contribute to the changes in the properties of the solar wind turbulence and may result in destructions of the association between solar wind turbulence and the magnetosphere. The present study provides the statistics of two-point simultaneous measurements of the turbulence properties in the solar wind and the magnetosheath based on Wind and THEMIS spacecraft data. Changes in the turbulence properties are analyzed for different background conditions. Solar wind bulk speed and temperature are shown to be the main factors that influence the modification of turbulence at the quasi-perpendicular bow shock at frequencies higher than the break frequency (ion transition range). Inside the magnetosheath, significant steepening of spectra occurs with an increase in temperature anisotropy without a connection to the upstream spectrum scaling that underlines the crucial role of the instabilities in turbulence properties behind the bow shock. [ABSTRACT FROM AUTHOR]

Alfvén-wave turbulence is known as a plasma heating mechanism associated with the acceleration of fast solar wind, found emanating from open magnetic fields adjacent to coronal holes. In this study, we expand the scope of this mechanism to investigate the thermodynamics of Alfvénic slow solar wind, a phenomenon originating from open fields near a streamer, as observed in recent inner heliospheric missions. We demonstrate a one-dimensional two-fluid model that incorporates three components: (1) low-frequency Alfvén-wave turbulence, serving as the primary dissipation mechanism, (2) a curved magnetic field that reproduces the streamer's boundary, and (3) the kinetic instabilities to address proton temperature anisotropy. Our findings suggest that this dissipation mechanism can be applied in common to both fast and Alfvénic slow solar winds. We identify the proton-cyclotron instability near the Sun and the oblique and parallel firehose instabilities occurring close to 1 au as crucial factors governing temperature anisotropy. This study contributes to our understanding of the complex thermodynamics of solar winds and provides valuable insights for future space missions. [ABSTRACT FROM AUTHOR]

Beach morphology assessment is very important for the sustainable development of beaches and the implementation of beach development activities through management plans. The present study focuses on assessing beach morphology and developing ecosystem-based conservative strategies to control beach erosion and improve beach safety along the two blue-flag certified beaches, Padubidri and Kasarkod, in Karnataka state. The bathymetry of the two beaches varies by gradient changes between the winter and monsoon seasons, and as a result, waves break at a distance of 15–25 m from the shore. The estimated seabed deposition between the winter and monsoon periods of 2020 is 10329 cu m and 59.36 cu m at the Padubidri and Kasarkod beaches, respectively. This study also provides the rate of shoreline change at two beaches along the coast for the period 2018–2022, as measured using geospatial technology and field investigation. The assessment revealed that the Kasarkod and Padubidri coasts experienced maximum erosion of 11.7% and 12.7%, respectively for five years. The projected shoreline changes under the climate change show erosion of 59.12 m on the northern side and accretion of about 16.13 m on the southern side of Kasarkod Beach, whereas on Padubidri Beach, erosion of 40 m on the central part of the beach between 2020 and 2030. The nearshore current magnitude is stronger at the coast of Padubidri than at Kasarkod during the study. The sediment movement from the Kamini River at the Hejamadi endpoint (southern part of Padubidri) shapes the Padubidri beach and causes accretion and erosion during winter and monsoon seasons respectively. However, these beaches are being protected by ecosystem-based conservative strategies such as beach vegetation and dune conservation through the Beach Environment and Aesthetics Management Services (BEAMS) program. Therefore, the assessment of beach morphology and conservation strategies provides a better beach management plan, to control beach erosion, and enhance beach stability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The investigation of plasma motions in the solar chromosphere is crucial for understanding the transport of mechanical energy from the interior of the Sun to the outer atmosphere and into interplanetary space. We report the finding of large-amplitude oscillatory transverse motions prevailing in the non-spicular Hα chromosphere of a small quiet region near the solar disk center. The observation was carried out on 2018 August 25 with the Microlensed Hyperspectral Imager (MiHI) installed as an extension to the spectrograph at the Swedish Solar Telescope (SST). MiHI produced high-resolution Stokes spectra of the Hα line over a two-dimensional array of points (sampled every 0.066″ on the image plane) every 1.33 s for about 17 min. We extracted the Doppler-shift-insensitive intensity data of the line core by applying a bisector fit to Stoke I line profiles. From our time–distance analysis of the intensity data, we find a variety of transverse motions with velocity amplitudes of up to 40 km s−1 in fan fibrils and tiny filaments. In particular, in the fan fibrils, large-amplitude transverse MHD waves were seen to occur with a mean velocity amplitude of 25 km s−1 and a mean period of 5.8 min, propagating at a speed of 40 km s−1. These waves are nonlinear and display group behavior. We estimate the wave energy flux in the upper chromosphere at 3 × 106 erg cm−2 s−1. Our results contribute to the advancement of our understanding of the properties of transverse MHD waves in the solar chromosphere. [ABSTRACT FROM AUTHOR]

Context. Small Solar System bodies (SSSBs) hold crucial information for understanding the formation and evolution of the Solar System. However, due to their considerable distance, small size, fast rotation, and a lack of prior information, the detection of these celestial bodies, especially their internal structures, faces numerous challenges. Aims. We explore whether the 3D structure of SSSBs can be reconstructed using monostatic radar. We investigated a more convenient observation mode and addressed the issue of the poor imaging quality of internal structures within existing imaging algorithms. Methods. Our study focused on a high-precision 3D imaging method for the internal structure of SSSBs based on radar signals. First, we considered a flyby observation mode that uses the spinning characteristics of the target for global observations, and we set up a scaled-down experimental system in the laboratory to simulate this observation mode. Next, we constructed a 3D printed physical surface model based on the shape of the asteroid 162173 Ryugu. We filled it with sand and inserted a small bottle containing different materials separately to construct two distinct layered analogs. The analogs were employed in laboratory measurements to acquire radar echoes, which were then inverted using both a classic back-projection (BP) algorithm and a modified multilayer back-projection (MLBP) method. Results. The results shown that the 3D surface structure of the target can be reconstructed well through the BP and MLBP algorithms. The MLBP algorithm exhibits a higher reconstruction accuracy for internal structures. Moreover, compared to the BP method, the MLBP method is less sensitive to the quality of echo signals, resulting in a relatively stable imaging performance. Conclusions. Our findings reveal that observing and reconstructing the high-precision structure of SSSBs is feasible through our proposed method. The observation mode, experimental setup, and analog modeling approach are widely applicable and can be applied in future research on the detection of SSSBs with more diverse and complex structures. [ABSTRACT FROM AUTHOR]

Context. Mercury presents a highly dynamic, small magnetosphere in which magnetic reconnection plays a fundamental role. Aim. We aim to model the global characteristics of magnetic reconnection in the Hermean environment. In particular, we focus on waves observed during the third BepiColombo flyby. Method. In this work, we used two fully kinetic three-dimensional (3D) simulations carried out with the iPIC3D code, which models the interaction of the solar wind with the Hermean magnetosphere. For the simulations, we used southward solar wind conditions that allow for a maximum magnetic coupling between the solar wind and the planet. Results. Our simulations show that a significant wave activity, triggered by magnetic reconnection, develops near the diffusion region in the magnetotail and propagates at large scales in the night-side magnetosphere. We see an increase in electron temperature close to the diffusion region and we specifically observe narrowband whistler waves developing near the reconnection region. These waves propagate nearly parallel to the magnetic field at frequency f ∼ 0.5fce. In addition to the electromagnetic component, these waves also exhibit an electrostatic one. Furthermore, we observe a strong electron temperature anisotropy, suggesting it plays a role as the source of these waves. [ABSTRACT FROM AUTHOR]

The geometry of a coronal hole (CH) affects the density profile of the reflected part of an incoming global coronal wave (CW). In this study, we perform for the first time magnetohydrodynamic (MHD) simulations of fast-mode MHD waves that interact with CHs of different geometries, such as circular, elliptic, convex, and concave shapes. We analysed the effect of these geometries on the density profiles of the reflected waves, and we generated the corresponding simulation-based time-distance plots. Within these time-distance plots, we determined regions that exhibit specific density features, such as large reflected density amplitudes. In a further step, these interaction features can be compared to actual observed CW–CH interaction events, which will enable us to explain interaction parameters of the observed interaction events, such as the density structure of the reflected wave. These parameters are usually difficult to understand comprehensively based on an analysis of the measurements alone. Moreover, we show that the interaction between a concave CH and CWs, whose density profile includes an enhanced as well as a depleted wave part, can lead to reflected density amplitudes that are more than twice larger than the incoming density amplitudes. Another effect of the interplay between the constructive and destructive interference of the reflected wave parts is a strongly depleted region in the middle of the CW–CH interaction process. In addition, we show that the choice of the path that is used to generate the time-distance plots is important and that this choice affects the interpretation of the CW–CH interaction results. [ABSTRACT FROM AUTHOR]

The transition of an impulsively excited kink oscillation of a solar coronal loop to an oscillation with a stationary amplitude, i.e. the damping pattern, is determined using the low-dimensional self-oscillation model. In the model, the decayless kink oscillations are sustained by the interaction of the oscillating loop with an external quasi-steady flow. The analytical solution is based on the assumption that the combined effect of the effective dissipation, for example, by resonant absorption, and interaction with an external flow, is weak. The effect is characterized by a dimensionless coupling parameter. The damping pattern is found to depend upon the initial amplitude and the coupling parameter. The approximate expression shows a good agreement with a numerical solution of the self-oscillation equation. The plausibility of the established damping pattern is demonstrated by an observational example. Notably, the damping pattern is not exponential, and the characteristic decay time is different from the time determined by the traditionally used exponential damping fit. Implications of this finding for seismology of the solar coronal plasmas are discussed. In particular, it is suggested that a very rapid, in less than the oscillation period, decay of the oscillation to the stationary level, achieved for larger values of the coupling parameter, can explain the relative rareness of the kink oscillation events. [ABSTRACT FROM AUTHOR]

The instabilities produced by a linear model of the tropical atmosphere coupled to a prognostic equation for water vapour are investigated. The basic model with no meridional wind supports unstable eastward‐propagating waves. For parameter regimes relevant to the Indo‐Pacific warm pool, the long‐time asymptotic behaviour of the unstable waves is found to be absolutely unstable, so that the amplitude of disturbances will grow in time at every point in the domain. The absolute instability of the system is realized at planetary length‐scales and intraseasonal frequencies. Other parameter choices for the system do not produce this same behaviour at these length‐ and time‐scales. It is shown that the resultant long‐time behaviour of the instability is characterized by roughly equal roles for temperature and moisture fluctuations in setting the thermodynamic tendency of the waves. With the inclusion of momentum damping, the phase speed of the absolutely unstable solution is about 7 m·$$ \cdotp $$s −1$$ {}^{-1} $$. Addition of a strong background meridional moisture gradient, as in recent studies on the Madden–Julian Oscillation (MJO), appears to remove the absolute instability from the system. In a background state that varies slowly in the zonal direction, it is shown analytically that localized regions of instability may be formed, again using parameter choices relevant to the warm pool. The dynamics and thermodynamics of these local instabilities show some correspondence with the observed development of the MJO as it propagates through the warm pool. [ABSTRACT FROM AUTHOR]

The BBGKY hierarchy in the Wigner representation is used with an extended Singwi‐Tosi‐Land‐Sjölander (STLS) ansatz for the two‐particle distribution function [H. Kählert, G. J. Kalman, and M. Bonitz, Phys. Rev. E 90, 011101 (2014)] to study the density response function and the dispersion relation of collective modes in a strongly coupled quantum system. It is shown that the local field correction (LFC) and the dispersion relation reduce to the results of the Quasi‐Localized Charge Approximation (QLCA) in the classical limit. In the quantum case, the LFC acquires a frequency‐dependence, similar to the quantum version of the STLS theory. The dispersion relation is governed by a generalization of the QLCA dynamical matrix. The results are expected to be relevant for the analysis of collective modes in quantum liquids with strong correlations. [ABSTRACT FROM AUTHOR]

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Parametric coupling of waves is one of the most efficient mechanisms of energy transfer that can lead to the growth or decay of waves. This transfer occurs at frequencies close to their natural frequencies. In partially ionized solar plasma, there are a multitude of waves that can undergo this process. Here, we study the parametric coupling of Alfvén waves propagating in a partially ionized solar plasma with ionization-recombination waves identified by our study to appear in a plasma in ionization non-equilibrium. Depending on the parameters that describe the plasma (density, temperature), coupling can lead to a parametric resonance. Our study determines the occurrence conditions of parametric resonance, by finding the boundaries between stable and unstable regions in the parameter space. Our results show that collisions and non-equilibrium recombination can both contribute to the onset of unstable behaviour of parametrically resonant Alfvén waves. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Partially ionized plasmas constitute an essential ingredient of the solar atmosphere, and ground- and space-based observations have pointed out the presence of oscillations in partially ionized solar plasmas such as chromosphere, photosphere, prominences or spicules, which have been interpreted in terms of magnetohydrodynamic waves. Our aim is to study the spatial behaviour of propagating weakly and fully nonlinear Alfvén waves, and the subsequent excitation of field-aligned motions and perturbations, when dissipative mechanisms, such as ambipolar diffusion and radiative losses, together with parametrized heating mechanisms, are taken into account. When only ambipolar diffusion is taken into account, first-order Alfvén waves as well as ponderomotive-driven perturbations are spatially damped, while field-aligned motions and perturbations representing propagating slow waves are undamped. These perturbations are damped when thermal effects are also considered and their damping lengths can be longer or shorter than those of ponderomotive-driven perturbations. Therefore, after the initial excitation, Alfvén waves and ponderomotive-driven perturbations could be quickly damped while slow waves still remain in the plasma, and vice versa. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Tidal turbine arrays have undergone extensive research to determine the optimal spacing for efficient performance and reduced wake generation. Small-scale laboratory tests are typically conducted to analyze wake structures prior to deployment. These tests often result in conditions of extreme blockage due to channel narrowing in comparison to turbine size. The primary objective of this study is to investigate flow behavior around turbines under blockage conditions and their performance close to the free surface, both in current-only and wave-and-current scenarios. The methodology employed a combination of blade element momentum theory and computational fluid dynamics (CFD) integrating a virtual blade model (VBM) code. The findings of this study indicate potential enhancements in tidal turbine array performance of up to 7% in lateral arrangements and 11% in streamwise arrangements under blockage conditions. The wake is significantly influenced by surface waves, which also contribute to increased downstream turbine performance. [ABSTRACT FROM AUTHOR]

It has been argued that the copper price exhibits "super-cycles" with periodicities of 30–60 years. Estimates of these super-cycles are typically generated by the bandpass filter. These filtered results are better interpreted as irregular episodic waves. The cyclical interpretation relies on an arbitrary separation between the cycle and an implicitly defined smooth trend. Analysis using the unobserved components model shows the price trend to be stochastic, not smooth. There is some evidence for short and poorly defined cycles but at best weak evidence for a long copper super-cycle. This finding is supported by examination of the price spectrum and generalizes to other non-ferrous metals. [ABSTRACT FROM AUTHOR]

As the number of satellites on orbit grows it is increasingly important to understand their operating environment. Physics‐based models can simulate the behavior of the Earth's radiation belts by solving a Fokker‐Planck equation. Three‐dimensional models use diffusion coefficients to represent the interactions between electromagnetic waves and the electrons. One‐dimensional radial diffusion models neglect the effects of energy diffusion and represent the losses due to the waves with a loss timescale. Both approaches may use pitch angle distributions (PADs) to create boundary conditions, to map observations from low to high equatorial pitch angles and to calculate phase‐space density from observations. We present a comprehensive set of consistent PADs and loss timescales for 2 ≤ L* ≤ 7, 100 keV ≤ E ≤ 5 MeV and all levels of geomagnetic activity determined by the Kp index. These are calculated from drift‐averaged diffusion coefficients that represent all the VLF waves that typically interact with radiation belt electrons and show good agreement with data. The contribution of individual waves is demonstrated; magnetosonic waves have little effect on loss timescales when lightning‐generated whistlers are present, and chorus waves contribute to loss even in low levels of geomagnetic activity. The PADs vary in shape depending on the dominant waves. When chorus is dominant the distributions have little activity dependence, unlike the corresponding loss timescales. Distributions peaked near 90° are formed by plasmaspheric hiss for L* ≤ 3 and E < 1 MeV, and by EMIC waves for L* > 3 and E > 1 MeV. When hiss dominates, increasing activity broadens the distribution but when EMIC waves dominate increasing activity narrows the distribution. Plain Language Summary: As the number of satellites on orbit grows it is increasingly important to understand their operating environment. Physics‐based models of the radiation belts can be used to model how the radiation environment varies with time. Three‐dimensional models typically include the effect of interactions between electromagnetic waves and electrons in the belts on both the motion and energy of the electrons. One‐dimensional models simplify the modeling by neglecting the effect of the waves on the energy of the electron and only consider how rapidly they are lost. Both types of model require an understanding of how electrons are distributed in the belts and how they are lost. We present calculations of the timescale for electron loss from the belts and for the shape of the distribution of electrons with equatorial pitch angle, a variable related to latitude, due to the combined effect of all the VLF waves that typically interact with radiation belt electrons. Our results show good agreement with the observations. They vary significantly with location, energy and geomagnetic activity, the influence of individual waves can be identified, and the model provides a useful resource for radiation belt models. Key Points: The combined effect of all the VLF waves that typically interact with radiation belt electrons is included in the calculationsWhen chorus is the dominant wave pitch angle distributions show little activity dependence, unlike the corresponding loss timescalesIncreasing geomagnetic activity tends to broaden the peak of the distributions dominated by hiss and narrow those dominated by EMIC waves [ABSTRACT FROM AUTHOR]