Prominent Oscillations Research Articles

Borehole Effects on Coaxial and Coplanar Logs of Triaxial Tools in Laminated Formations with Anisotropic Shale Host

This paper studies the borehole effect in the triaxial induction logs within sand-shale laminated models with isotropic and anisotropic shale laminae with transverse isotropy. This study compares results from a 3D Vector Finite Element program (with borehole) and a 1D-Analytic code (no borehole). In comparison with the coaxial configuration, the vertical coplanar logs show a stronger horning effect in front of the laminated pack boundaries; a more intense skin effect to the conductivity media; and a more prominent oscillation within the laminated formation. In addition, feature changes (angular or smooth shapes) occur on the coaxial and coplanar responses as the dipping angle varies. The sensitivities of the logs to the anisotropy and borehole are opposite, i.e., for small angles where the coaxial is least sensitive, the coplanar is most sensitive, and for large angles where the coaxial is most sensitive, the coplanar is least sensitive. The main physical cause of these opposite behaviors to the anisotropy and borehole effect is the same: the weight of the horizontal magnetic component of the horizontal dipole contribution on the coaxial and coplanar dipping logs since it is the only one of the four magnetic field components that has anisotropy sensitivity and strongest skin effect.

Distinctive Effects of D1 and D2 Receptor Agonists on Cortico-Basal Ganglia Oscillations in a Rodent Model of L-DOPA-Induced Dyskinesia

L-DOPA-induced dyskinesia (LID) in Parkinson’s disease has been linked to oscillatory neuronal activities in the cortico-basal ganglia network. We set out to examine the pattern of cortico-basal ganglia oscillations induced by selective agonists of D1 and D2 receptors in a rat model of LID. Local field potentials were recorded in freely moving rats using large-scale electrodes targeting three motor cortical regions, dorsomedial and dorsolateral striatum, external globus pallidus, and substantial nigra pars reticulata. Abnormal involuntary movements were elicited by the D1 agonist SKF82958 or the D2 agonist sumanirole, while overall motor activity was quantified using video analysis (DeepLabCut). Both SKF82958 and sumanirole induced dyskinesia, although with significant differences in temporal course, overall severity, and body distribution. The D1 agonist induced prominent narrowband oscillations in the high gamma range (70–110 Hz) in all recorded structures except for the nigra reticulata. Additionally, the D1 agonist induced strong functional connectivity between the recorded structures and the phase analysis revealed that the primary motor cortex (forelimb area) was leading a supplementary motor area and striatum. Following treatment with the D2 agonist, narrowband gamma oscillations were detected only in forelimb motor cortex and dorsolateral striatum, while prominent oscillations in the theta band occurred in the globus pallidus and nigra reticulata. Our results reveal that the dyskinetic effects of D1 and D2 receptor agonists are associated with distinct patterns of cortico-basal ganglia oscillations, suggesting a recruitment of partially distinct networks.

Sex-specific alterations in corticotropin-releasing factor regulation of coerulear-cortical network activity

The locus coeruleus (LC)-norepinephrine system is a stress responsive system that regulates arousal and cognitive functions through extensive projections, including to the prefrontal cortex. LC-cortical circuits are activated by stressors, and this activation is thought to contribute to stress-induced impairments in executive function. Because corticotropin-releasing factor (CRF) is a mediator of stress-induced LC activation, we examined the effects of CRF administered into the LC of male and female rats on network activity of two functionally distinct regions of the PFC, the medial PFC (mPFC) and the orbitofrontal cortex (OFC). Network activity, measured as local field potentials, was recorded in awake animals before and after intra-LC infusion of aCSF or CRF (2 or 20 ng). CRF had qualitatively distinct effects on network activity in males and females with respect to dose, region and timecourse. CRF (20 ng) produced a prominent theta oscillation (7–9 Hz) selectively in female rats shortly after LC infusion and 20 min later. In contrast, in male rats, CRF (2 and 20 ng) decreased the amplitude of power in the 4–6 Hz range in the mPFC 10 min after injection. Lastly, CRF (20 ng) increased mPFC-OFC coherence in females and decreased mPFC-OFC coherence in males. In sum, these results show sex differences in CRF modulation of the LC-norepinephrine system that regulates prefrontal cortical networks, which may underlie sex differences in cognitive and behavioral responses to stress.

The Effect of Thermal Misbalance on Slow Magnetoacoustic Waves in a Partially Ionized Prominence-Like Plasma

Solar prominences are partially ionized plasma structures embedded in the solar corona. Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences, which have been interpreted in terms of standing or propagating MHD waves. Some of these observations suggest that slow magnetoacoustic waves could be responsible for these oscillations and have provided us with evidence about their damping/amplification with very small ratios between damping/amplifying times and periods, which have been difficult to explain from a theoretical point of view. Here we investigate the temporal behavior of non-adiabatic, slow, magnetoacoustic waves when a heating–cooling misbalance is present. The influence of optically thin losses and of a general heating term, in which density and temperature dependence can be modified, as well as the effect of partial ionization have been considered. Furthermore, a tentative example of how, using observational data, the observed ratio between damping/amplifying times and periods could be matched with those theoretically obtained is shown. In summary, different combinations of radiative losses, heating mechanisms, and typical wavenumbers, together with the effect of partial ionization, could provide a theoretical tool able to reproduce observational results on small-amplitude oscillations in prominences.

Automatic detection technique for solar filament oscillations in GONG data

Context. Solar filament oscillations have been known for decades. The new capabilities of the new telescopes have afforded routine observations of these periodic motions. Oscillations in filaments show key aspects of their structure. A systematic study of filament oscillations over the solar cycle can shed light on the evolution of the prominences. Aims. This work is a proof of concept that aims to automatically detect and parametrise these oscillations using Hα data from the GONG network of telescopes. Methods. The proposed technique studies the periodic fluctuations of every pixel of the Hα data cubes. Using the fast Fourier transform, we computed the power spectral density (PSD). We defined a criterion to consider whether it is a real oscillation or a spurious fluctuation. This consisted of considering that the peak in the PSD must be greater than several times the background noise with a confidence level of 95%. The background noise is well fitted to a combination of red and white noise. We applied the method to several observations that were reported in the literature to determine its reliability. We also applied the method to a test case, which was a data set in which the oscillations of the filaments were not known a priori. Results. The method shows that the filaments contain areas in which the PSD is above the threshold value. The periodicities we obtained generally agree with the values that were obtained by other methods. In the test case, the method detects oscillations in several filaments. Conclusions. We conclude that the proposed spectral technique is a powerful tool for automatically detecting oscillations in prominences using Hα data.

Effect of aluminum foam on pressure oscillation of premixed methane-air deflagrations

The effect of aluminum foam on the pressure oscillation of premixed methane-air deflagrations was investigated using experiments performed in an empty duct and a duct with aluminum foam attached to the upper and lower walls. For a fair comparison, the passage areas of the two ducts are identical when considering a 10 mm thickness of the porous medium. The flame propagation, pressure oscillation, and interaction mechanism between the acoustic wave and flame front are discussed by comparing the flame structure and pressure waveform during premixed methane-air mixture deflagration. The results demonstrate that for the empty duct configuration, the flame propagates as a cellular structure and then evolves into an oscillating flame when approaching the closed end of the duct. The coupling effect of the flame and acoustic waves induces the flame to oscillate violently as the distance from the ignition source to the closed end of the duct (i.e., the ignition position) increases to a threshold value. The magnitude of pressure oscillation increases as the distance between the ignition source and the closed end of the duct increases and reaches a maximum when the ignition position is 700 mm from the closed end. Additionally, the pressure oscillation is consistent with the flame oscillation. This oscillation results in a large deflagration pressure and a high rate of pressure rise. By contrast, the aluminum foam-laden duct completely suppresses the oscillation of the premixed methane-air deflagrations for all ignition positions. The aluminum foam inhibits the coupling effect and consequently restrains the prominent deformation and oscillation of the flame front. Flame oscillation vanishes as the acoustic damping coefficient increases. In this case, there is no oscillation and the leading position of the left flame exhibits a linear relationship with time. Whether the foam material has an inhibitive effect on the deflagration pressure depends on the ignition position. The aluminum foam enhances the deflagration pressure when the ignition position is 100 mm from the closed end, with a 29% increase in the maximum overpressure. By contrast, the aluminum foam attenuates the deflagration pressure for other ignition positions, with a maximum drop ratio of 61.7% at the ignition position being 700 mm from the closed end.

Topographic Rossby Wave‐Modulated Oscillations of Dense Overflows

AbstractThe global supply of Antarctic Bottom Water (AABW) is sourced from a handful of dense overflows. Observations from the Weddell Sea indicate that the overflow there exhibits prominent oscillations accompanied by dense eddies, while the Ross Sea overflow shows no significant oscillations other than tides, yet the genesis of these oscillations and their role in mediating AABW export remain poorly understood. Here idealized model simulations are used to investigate the dynamics of these oscillations. It is shown that the dominant oscillations result from the formation of Topographic Rossby waves (TRWs) associated with baroclinic instability of the dense overflow. A key finding is that the TRWs can feed back onto the dense overflow, producing coherent subsurface eddies of the same frequency. A series of sensitivity experiments reveal that these behaviors depend strongly on the local environment: steep topographic slopes suppress the baroclinic growth of TRWs, while strong downstream along‐slope flows suppress the upstream propagation of TRW energy and genesis of subsurface eddies. These results explain the varying prevalence of different oscillatory phenomena observed across different dense overflow regimes.

Formation of an Electron-Phonon Bifluid in Bulk Antimony

The flow of charge and entropy in solids usually depends on collisions decaying quasiparticle momentum. Hydrodynamic corrections can emerge, however, if most collisions among quasiparticles conserve momentum and the mean-free path approaches the sample dimensions. Here, through a study of electrical and thermal transport in antimony (Sb) crystals of various sizes, we document the emergence of a two-component fluid of electrons and phonons. Lattice thermal conductivity is dominated by electron scattering down to 0.1 K and displays prominent quantum oscillations. The Dingle mobility does not vary despite an order-of-magnitude change in transport mobility. The Bloch-Grüneisen behavior of electrical resistivity is suddenly aborted below 15 K and replaced by a quadratic temperature dependence. At the Kelvin temperature range, the phonon scattering time and the electron-electron scattering time display a similar amplitude and temperature dependence. Taken together, the results draw a consistent picture of a bifluid where frequent momentum-conserving collisions between electrons and phonons dominate the transport properties.Received 11 January 2022Revised 1 April 2022Accepted 7 June 2022DOI:https://doi.org/10.1103/PhysRevX.12.031023Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasThermal conductivityTransport phenomenaCondensed Matter, Materials & Applied Physics

The enigma of infra-slow fluctuations in the human EEG.

Spontaneous Infra-Slow Fluctuations (ISFs) of the human EEG (EEG-ISFs) were discovered 60 years ago when appropriate amplifiers for their recordings were designed. To avoid skin-related artifacts the recording of EEG-ISFs required puncturing the skin under the electrode. In the beginning of the 21st century the interest in EEG-ISFs was renewed with the appearance of commercially available DC-coupled amplified and by observation of ISFs of the blood oxygen level–dependent (BOLD) functional magnetic resonance imaging signal at a similar frequency. The independent components of irregular EEG-ISFs were shown to correlate with BOLD signals which in turn were driven by changes in arousal level measured by galvanic skin response (GSR), pupil size and HRV. There is no consensus regarding the temporal organization of EEG-ISFs: some studies emphasize the absence of peaks on EEG-ISFs spectra, some studies report prominent oscillations with frequency around 0.1 or 0.02 Hz, while some emphasize multiple discrete infraslow oscillations. No studies used parameters of EEG-ISFs as neuromarkers to discriminate psychiatric patients from healthy controls. Finally, a set of working hypotheses is suggested that must be tested in future research to solve the enigma of EEG-ISFs.

Intraseasonal Oscillatory Modes in the Eastern Mediterranean Sea

Abstract The intraseasonal oscillations (ISOs) in sea currents in the eastern Mediterranean Sea near the central coast of Israel were analyzed by examining the velocity components of the sea currents at different depths as measured by acoustic Doppler current profilers located at various depths between 0 and 675 m. The total period covered by the observations was from December 2016 to May 2018. Prominent intraseasonal oscillations, much stronger than tidal velocity components, were observed in the upper part of the sea, at 30–70 m. The amplitudes of these oscillations are between 4 and 10 cm s−1 and their periods are 7, 11, 22, and 34–36 days. The strongest oscillations are found in the boreal winter. The ISOs in the sea currents were apparently induced by corresponding oscillations found in atmospheric wind velocity over the eastern Mediterranean at the surface and at 500 and 250 hPa, as suggested by the high correlations, 0.6–0.9, between the wind velocity components of the oscillatory modes in the atmosphere and the velocity component of the oscillatory modes in the sea currents with similar periods. We propose that the source of the ISOs in the atmosphere over the eastern Mediterranean is the South Asian jet wave train. The track of this wave train passes over the eastern Mediterranean, and the periods of the ISOs in the wave train are in the same band as the oscillations found here. The wave train is equivalently barotropic and strongest in the upper troposphere. This property of the wave train can explain the high correlation found between the oscillatory modes of wind velocity at 250 or 500 hPa and those in the sea currents. In all the cases besides the 7-day oscillatory mode, the significant oscillatory modes found at 250 or 500 hPa are also significant in the velocity components of the surface wind.

Effect of obstacle location on explosion dynamics of premixed H2/CO/air mixtures in a closed duct

An experimental study was presented to investigate the effect of obstacle location (OL) on explosion dynamics of premixed H2/CO/air mixtures. A fence-type obstacle providing the blockage ratio of 0.5 was mounted in the closed duct, and the distance from the ignition end increased from 100 mm to 600 mm. Therefore, the effect of the obstacle on flame exponential acceleration stage, flame deceleration stage, and tulip flame stage had been comprehensively discussed. When OL ≤ 400 mm, the turbulent finger-shaped flame front will invert into the tulip shape after the flame propagates through the obstacle channel. The competition between the flamelets’ backward movements induced by the vortex motion and forward movement induced by the squish flow causes the turbulent finger-shaped flame front’s inversion. The pressure dynamics are discussed in conjunction with flame tip dynamics. The prominent flame deformation and oscillation after the tulip flame is caused by the interaction of flame and pressure waves. However, the pressure waves make no difference on the finger-shaped flame front inversion. This indicates that the flame front inversion after the obstacle is a pure hydrodynamic phenomenon. What’s more, for a given hydrogen volume fraction, the flame duration time first decreases and then decreases with obstacle location, the maximum flame tip speed and the maximum overpressure first increases and then decreases with obstacle location, and the maximum explosion severity occurs at OL = 400 mm.

Influence of Anthropogenic Activities on Elevation‐Dependent Weakening of Annual Temperature Cycle Amplitude Over the Tibetan Plateau

AbstractThe annual cycle is the dominant component and the most prominent climate oscillation for the temperature variation over the Tibetan Plateau (TP). Identifying the relative contribution of anthropogenic and natural forcing to the changes in the annual cycle, namely, detection and attribution, is an important aspect for mountainous climate change research. The present study documents the elevation dependence of the trend in the annual temperature cycle (ATC) amplitude over the TP and detects the influence of anthropogenic activities on it. An elevation‐dependent weakening of the ATC amplitude occurs over the TP during the period 1961–2014. This variation with altitude can mainly be ascribed to the seasonal difference in warming. The influence of anthropogenic activities is detectable, with increased aerosols being the main contributor. Under aerosol‐only forcing, the larger decrease in snow‐related albedo at higher altitudes in winter can explain the amplified negative tendency of the ATC amplitude with elevation.

Extension and validation of the pendulum model for longitudinal solar prominence oscillations

Context.Longitudinal oscillations in prominences are common phenomena on the Sun. These oscillations can be used to infer the geometry and intensity of the filament magnetic field. Previous theoretical studies of longitudinal oscillations made two simplifying assumptions: uniform gravity and semicircular dips on the supporting flux tubes. However, the gravity is not uniform and realistic dips are not semicircular.Aims.Our aim is to understand the effects of including the nonuniform solar gravity on longitudinal oscillations and explore the validity of the pendulum model with different flux-tube geometries.Methods.We first derived the equation describing the motion of the plasma along the flux tube including the effects of nonuniform gravity, yielding corrections to the original pendulum model. We also computed the full numerical solutions for the normal modes and compared them with the new pendulum approximation.Results.We find that the nonuniform gravity introduces a significant modification in the pendulum model. We also found a cut-off period; i.e., the longitudinal oscillations cannot have a period longer than 167 min. In addition, considering different tube geometries, the period depends almost exclusively on the radius of curvature at the bottom of the dip.Conclusions.We conclude that nonuniform gravity significantly modifies the pendulum model. These corrections are important for prominence seismology, because the inferred values of the radius of curvature and minimum magnetic-field strength differ substantially from those of the old model. However, we find that the corrected pendulum model is quite robust and is still valid for noncircular dips.

Quantum Oscillations in Noncentrosymmetric Weyl Semimetal SmAlSi

As a new type of quantum state of matter hosting low energy relativistic quasiparticles, Weyl semimetals (WSMs) have attracted significant attention for scientific community and potential quantum device applications. In this study, we present a comprehensive investigation of the structural, magnetic, and transport properties of noncentrosymmetric RAlSi (R = Sm, Ce), which have been predicted to be new magnetic WSM candidates. Both samples exhibit nonsaturated magnetoresistance, with about 900% and 80% for SmAlSi and CeAlSi, respectively, at temperature of 1.8 K and magnetic field of 9 T. The carrier densities of SmAlSi and CeAlSi exhibit remarkable change around magnetic transition temperatures, signifying that the electronic states are sensitive to the magnetic ordering of rare-earth elements. At low temperatures, SmAlSi reveals prominent Shubnikov-de Haas oscillations associated with the nontrivial Berry phase. High-pressure experiments demonstrate that the magnetic order is robust and survival under high pressure. Our results would yield valuable insights into WSM physics and potentials in applications to next-generation spintronic devices in the RAlSi (R = Sm, Ce) family.

Prominence oscillations activated by an EUV wave

Prominence oscillations are one of interesting phenomena in the solar atmosphere, which can be utilized to infer the embedded magnetic field magnitude. We present here the transverse oscillations of two different prominences located at the East solar limb on 2011 February 11 using the multi-wavebands data of the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) satellite. A prominence eruption was observed towards the east direction with an average speed of ≈ 275 km s−1. The eruption is fitted with the combination of a linear and an exponential functions of time. An extreme ultraviolet (EUV) wave event was associated with the prominence eruption. This EUV wave triggered the oscillations of both prominences on the East limb. We computed the period of each prominence using the wavelet analysis method. The oscillation period varies from 14 to 22 min. The magnetic field of the prominences was derived, which ranges from 14 to 20 G.

AstroSat detection of a quasi-periodic oscillation at ∼42 Hz in Cygnus X-2

ABSTRACT We report the results of AstroSat observations of Cygnus X-2 during 2016 February. The source’s power density spectrum generated using Large Area X-ray Proportional Counter (LAXPC) data revealed the presence of a prominent quasi-periodic oscillation (QPO) at ∼42 Hz with broad-band continuum noise at lower frequencies at ∼10 Hz. The large effective area of LAXPC at ≳30 keV allowed for an unprecedented study of the energy dependence of the QPO and the broad noise continuum. The fractional rms increases with energy, and its shape is similar for both the QPO and the continuum noise, suggesting a common radiative origin. However, while the QPO exhibits hard time-lags, with the high-energy photons lagging the low ones by a few milliseconds, the continuum noise shows the opposite behaviour. The photon spectrum from Soft X-ray Imaging Telescope and LAXPC in 0.7–30 keV band comprises the soft component from a disc and a hard Comptonized component from a hot corona. While the energy dependence of the rms shows that the QPO and the continuum noise variability are dominated by the Comptonized component, the change in sign of the time-lag suggests that the dynamic origin of the QPO may be in the disc while the noise continuum may originate from the corona.

Multi-threaded prominence oscillations triggered by a coronal shock wave

Context. Understanding the interplay between ubiquitous coronal shock waves and the resulting prominence oscillations is a key factor in improving our knowledge of prominences and the solar corona overall. In particular, prominences are a key element of the solar corona and represent a window into an as yet unexplained processes in the Sun’s atmosphere. Aims. To date, most studies on oscillations of prominences have ignored their finer structure and analyzed them strictly as monolithic bodies. In this work, we study the causal relations between a localised energy release and a remote prominence oscillation, where the prominence has a realistic thread-like structure. Methods. In our work, we used an open source magnetohydrodynamic code known as MPI-AMRVAC to create a multi-threaded prominence body. In this domain, we introduced an additional energy source from which a shock wave originates, thereby inducing prominence oscillation. We studied two cases with different source amplitudes to analyze its effect on the oscillations. Results. Our results show that the frequently used pendulum model does not suffice to fully estimate the period of the prominence oscillation, in addition to showing that the influence of the source and the thread-like prominence structure needs to be taken into account. Repeated reflections and transmissions of the initial shock wave occur at the specific locations of multiple high-temperature and high-density gradients in the domain. This includes the left and right transition region located at the footpoints of the magnetic arcade, as well as the various transition regions between the prominence and the corona. This results in numerous interferences of compressional waves propagating within and surrounding the prominence plasma. They contribute to the restoring forces of the oscillation, causing the period to deviate from the expected pendulum model, in addition to leading to differences in attributed damping or even growth in amplitude between the various threads. Along with the global longitudinal motion that result from the shock impact, small-scale transverse oscillations are also evident. Multiple high-frequency oscillations represent the propagation of magnetoacoustic waves. The damping we see is linked to the conversion of energy and its exchange with the surrounding corona. Our simulations demonstrate the exchange of energy between different threads and their different modes of oscillation.

Delta Oscillations Coordinate Intracerebellar and Cerebello-Hippocampal Network Dynamics during Sleep.

During sleep, the widespread coordination of neuronal oscillations across both cortical and subcortical brain regions is thought to support various physiological functions. However, how sleep-related activity within the brain's largest sensorimotor structure, the cerebellum, is multiplexed with well-described sleep-related mechanisms in regions such as the hippocampus remains unknown. We therefore simultaneously recorded from the dorsal hippocampus and three distinct regions of the cerebellum (Crus I, lobule VI, and lobules II/III) in male mice during natural sleep. Local field potential (LFP) oscillations were found to be coordinated between these structures in a sleep stage-specific manner. During non-REM sleep, prominent δ frequency coherence was observed between lobule VI and hippocampus, whereas non-REM-associated hippocampal sharp-wave ripple activity evoked discrete LFP modulation in all recorded cerebellar regions, with the shortest latency effects in lobule VI. We also describe discrete phasic sharp potentials (PSPs), which synchronize across cerebellar regions and trigger sharp-wave ripple suppression. During REM, cerebellar δ phase significantly modulated hippocampal theta frequency, and this effect was greatest when PSPs were abundant. PSPs were phase-locked to cerebellar δ oscillation peak and hippocampal theta oscillation trough, respectively. Within all three cerebellar regions, prominent LFP oscillations were observed at both low (δ, <4 Hz) and very high frequencies (∼250 Hz) during non-REM and REM sleep. Intracerebellar cross-frequency analysis revealed that δ oscillations modulate those in the very high-frequency range. Together, these results reveal multiple candidate physiological mechanisms to support "offline," bidirectional interaction within distributed cerebello-hippocampal networks.SIGNIFICANCE STATEMENT Sleep is associated with widespread coordination of activity across a range of brain regions. However, little is known about how activity within the largest sensorimotor region of the brain, the cerebellum, is both intrinsically organized and links with higher-order structures, such as the hippocampus, during sleep. By making multisite local field potential recordings in naturally sleeping mice, we reveal and characterize multiple sleep stage-specific physiological mechanisms linking three distinct cerebellar regions with the hippocampus. Central to these physiological mechanisms is a prominent δ (<4 Hz) oscillation, which temporally coordinates both intracerebellar and cerebello-hippocampal network dynamics. Understanding this distributed network activity is important for gaining insight into cerebellar contributions to sleep-dependent processes, such as memory consolidation.

Day‐To‐Day Variability of the MLT DE3 Using Joint Analysis on Observations From TIDI‐TIMED and a Meteor Radar Meridian Chain

AbstractIn the present work, daily variation of eastward propagating diurnal tide with zonal‐wave number 3 (DE3) is derived from joint analysis on observations from Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer and a meteor radar chain around meridian 120°E during years of 2012–2015 and 2018–2020 via a novel method. Together with empirical tidal modes (ETMs), which are based on the Global Scale Wave Model, daily DE3 in horizontal winds are extracted. ETMs characterize the two‐dimensionally latitude‐altitudinal tidal structure with consideration of tidal dissipation, and thus makes it possible to obtain the DE3 tide extending to pole‐to‐pole in latitudes and covering 80–140 km on altitudes. Quantitatively analyzing day‐to‐day variability of mesosphere and lower thermosphere DE3 reveals that the variation of tidal phase is the main contributor to the DE3 day‐to‐day variability for both zonal and meridional winds. The strength of tidal‐phase induced variability has a clear seasonal dependence that is strong around June and December solstices. Prominent semiannual oscillation (SAO) for zonal (∼16%) and meridional (∼24%) winds are revealed, and annual oscillation (AO) is superposed on the SAO for the DE3 in meridional winds (∼9%). Tidal‐phase induced variability is generally stronger in solar minima (2018–2020) than that in solar maxima (2013–2015). Furthermore, a comparison with simulations using the Whole Atmosphere Community Climate Model eXtended is discussed. The simulations confirm that the primary role of tidal‐phase variations on the day‐to‐day variability. The model does not reproduce the SAO as shown in observations, while the AO in meridional winds is simulated well.

F-electron hybridised Fermi surface in magnetic field-induced metallic YbB12

The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB6 is a subject of intense inquiry. Here we shed light on this question by accessing quantum oscillations in the high magnetic field-induced metallic regime above ≈47 T in YbB12, which we compare with the unconventional insulating regime. In the field-induced metallic regime, we find prominent quantum oscillations in the electrical resistivity characterised by multiple frequencies and heavy effective masses. The close similarity in Lifshitz-Kosevich low-temperature growth of quantum oscillation amplitude in insulating YbB12 to field-induced metallic YbB12, points to an origin of quantum oscillations in insulating YbB12 from in-gap neutral low energy excitations. Higher frequency Fermi surface sheets of heavy quasiparticle effective mass emerge in the field-induced metallic regime of YbB12 in addition to multiple heavy Fermi surface sheets observed in both insulating and metallic regimes. f-electron hybridisation is thus observed to persist from the unconventional insulating to the field-induced metallic regime of YbB12, in contrast to the unhybridised conduction electron Fermi surface observed in unconventional insulating SmB6. Our findings thus require an alternative model for YbB12, of neutral in-gap low energy excitations, wherein the f-electron hybridisation is retained.