Impulsive Events Research Articles

Extent and Volume of Lava Flows Erupted at 9°50′N, East Pacific Rise in 2005–2006 From Autonomous Underwater Vehicle Surveys

AbstractSeafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid‐ocean ridges. Volcanic eruptions in 2005–2006 at 9°50′N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near‐bottom bathymetric data. We present near‐bottom data collected during 19 autonomous underwater vehicle (AUV) Sentry dives at 9°50′N in 2018, 2019, and 2021. The resulting 1 m‐resolution bathymetric grid and 20 cm‐resolution sidescan sonar images cover 115 km2, and span the entire area of the 2005–2006 eruptions, including an 8 km2 pre‐eruption survey collected with AUV ABE in 2001. Pre‐ and post‐eruption surveys, combined with sidescan sonar images and seismo‐acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005–2006 eruptions, lava flowed up to ∼3 km away from the axial summit trough, covering an area of ∼20.8 km2; ∼50% larger than previously thought. Where pre‐ and post‐eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from ∼1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that ∼57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9°50′N area.

A Physical Interpretation of Asymmetric Growth and Decay of the Geomagnetic Dipole Moment

AbstractObservations of relative paleointensity reveal several forms of asymmetry in the time dependence of the virtual axial dipole moment (VADM). Slow decline of the VADM into a reversal is often followed by a more rapid rise back to a quasi‐steady state. Asymmetry is also observed in trends of VADM during times of stable polarity. Trends of increasing VADM over time intervals of a few 10s of kyr are more intense and less frequent than decreasing trends. We examine the origin of this behavior using stochastic models. The usual (Langevin) model can account for asymmetries during reversals, but it cannot reproduce the observed asymmetry in trends during stable polarity. Better agreement is achieved with a different class of stochastic models in which the dipole is generated by a series of impulsive events in time. The timing of each event occurs randomly as a Poisson process and the amplitude is also randomly distributed. Predicted trends replicate the observed asymmetry when the generation events are large and the recurrence time is long (typically longer than 3 kyr). Large and infrequent generation events argue against dipole generation by small‐scale turbulent flow. Instead, the observations favor a mechanism that relies on expulsion of poloidal magnetic field from the core.

Impulsivity and Stressful Life Events Independently Relate to Problematic Substance Use in At-Risk Adolescents

Impulsivity and Stressful Life Events Independently Relate to Problematic Substance Use in At-Risk Adolescents

Secular variation signals in magnetic field gradient tensor elements derived from satellite-based geomagnetic virtual observatories

SUMMARYWe present local time-series of the magnetic field gradient tensor elements at satellite altitude derived using a Geomagnetic Virtual Observatory (GVO) approach. Gradient element time-series are computed in 4-monthly bins on an approximately equal-area distributed worldwide network. This enables global investigations of spatio-temporal variations in the gradient tensor elements. Series are derived from data collected by the Swarm and CHAMP satellite missions, using vector field measurements and their along-track and east–west differences, when available. We find evidence for a regional secular variation impulse (jerk) event in 2017 in the first time derivative of the gradient tensor elements. This event is located at low latitudes in the Pacific region. It has a similar profile and amplitude regardless of the adopted data selection criteria and is well fit by an internal potential field. Spherical harmonic models of the internal magnetic field built from the GVO gradient series show lower scatter in near-zonal harmonics compared with models built using standard GVO vector field series. The GVO gradient element series are an effective means of compressing the spatio-temporal information gathered by low-Earth orbit satellites on geomagnetic field variations, which may prove useful for core flow inversions and in geodynamo data assimilation studies.

Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field Line Braiding Model with Compound Injections

Abstract We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly variable over more than two orders of magnitude, even if the source ratio is at the nominal value. Assuming a 3He/4He source ratio of 10% in impulsive 3He-rich events and the same spatial offset of the source regions, the 3He/4He ratio at observation sites also vary considerably. The variability of the ion composition ratios depends on the radial distance, which can be tested by observations made at different radial locations. We discuss the implications of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.

Single- and Multi-Carrier Systems Affected by Impulsive Noise: Covid-19 View

In this work we present a fully stochastic model of performance analysis of single- and multi-carrier modulations (SCM and MCM) in communication systems affected by impulsive noise. The key performance of the model is the symbol error rate (SER), which is fully determined as a function of the system parameters, including the frame length, symbol power, white noise power, impulsive noise power, and the probability of the impulse events. We derive closed-form analytical expressions for the systems SER and compare them with simulation results, showing very good agreement for all the impulsive noise scenarios. Specifically, we show under which conditions a MCM system performs better than a SCM one, and vice versa, which can be used to apply an optimal switching policy that minimizes SER. The model developed for SCM and MCM systems is conceptually applied to the Covid-19 phenomenology and, consequently, the results obtained for SCM and MCM scenarios are interpreted to inform decision and management policies of social distancing (lock/roam). Specifically, we also show when the “roam” strategy performs better than the “lock” strategy, and vice versa, thus enabling the design of an optimal control policy that minimizes the mortality rate (MR). However, the proposed model for Covid-19, which assumes a similarity with SCM/MCM systems, may not be easy to be tested in practice in the absence of adequate statistical data. Therefore, any management decision should not be based (only) on the proposed model adapted to Covid-19, and necessarily requests the integration of experts opinions.

A Multi-wavelength Analysis of Small-scale Brightenings Observed by IRIS

Abstract Small-scale brightenings in solar atmospheric observations are a manifestation of heating and/or energy transport events. We present statistical characteristics of brightenings from a new detection method applied to 1330, 1400, and 2796 Å IRIS slit-jaw image time series. A total of 2377 events were recorded that coexist in all three channels, giving high confidence that they are real. Of these, ≈1800 were spatially coherent, equating to event densities of ∼9.7 × 10−5 arcsec−2 s−1 within a 90″ × 100″ FOV over 34.5 minutes. Power-law indices estimates are determined for total brightness (2.78 < α < 3.71), maximum brightness (3.84 < α < 4.70), and average area (4.31 < α < 5.70) distributions. Duration and speed distributions do not obey a power law. A correlation is found between the events’ spatial fragmentation, area, and duration, and a weak relationship with total brightness, showing that larger/longer-lasting events are more likely to fragment during their lifetime. Speed distributions show that all events are in motion, with an average speed of ∼7 km s−1. The events’ spatial trajectories suggest that cooler 2796 Å events tend to appear slightly later and occupy a different position/trajectory than the hotter channel results. This suggests that either many of these are impulsive events caused by reconnection, with subsequent rapid cooling, or that the triggering event occurs near the TR, with a subsequent propagating disturbance to cooler atmospheric layers. The spatial distribution of events is not uniform, with broad regions devoid of events. A comparison of spatial distribution with properties of other atmospheric layers shows a tentative connection between high magnetic field strength, the corona’s multi-thermality, and high IRIS brightening activity.

3He-rich solar energetic particle events observed on the first perihelion pass of Solar Orbiter

We report observations of five impulsive solar energetic particle (SEP) events observed inside 1 au during the first perihelion pass of the Solar Orbiter mission, which was launched in February 2020. These small events were all reasonably associated with active regions observed from Earth but which had rotated out of view by the time of the Solar Orbiter observations. Even though most of the events were small, their spectral forms,3He content, and association with type III bursts convincingly identifies them as3He-rich impulsive SEP events with properties similar to those previously observed at 1 au. Three of the events showed fast ion rise times, and two of them had long-lasting anisotropies consistent with the Compton-Getting effect.

3D non-driven magnetic reconnection at multiple separators

Separators are important topological features of magnetic configuration for magnetic reconnection, commonly found in the solar plasma. They are located at the boundary shared among four distinctive flux domains; therefore, current layers easily build up around them. This paper aims to explore non-driven magnetic reconnection at multiple separators since little information is available about it. We have done two sets of experiments: non-resistive magnetohydrodynamic (MHD) relaxation and resistive MHD reconnection of a magnetic configuration consisting of two null points alongside their associated spines and three non-potential separators, which connect the same two null points. We used the LARE3D code for this purpose. The main current layers are formed along these separators where reconnection takes place. The reconnection occurs in two distinct phases: fast–strong and slow–weak. Most of the current dissipates at a fast rate, through Ohmic heating, during the fast–strong phase. The short-lived impulsive bursty reconnection events occur randomly in the slow–weak phase, while viscous heating exceeds Ohmic heating in this phase. The electric field component is parallel to field lines along the separators; likewise, the rate of reconnection along each of them evolved over time. However, work on separator reconnection has a strong potential to understand the underlying physics.

Particle-in-cell Simulation of 3He Enrichment in Solar Energetic Particle Events

Abstract 3He enrichment is one distinctive feature of impulsive solar energetic particle events. This study is designed to investigate the process of plasma wave–particle resonance, which plays a key role in selectively accelerating heavy ions. We apply a 1.5 dimensional particle-in-cell simulation to model the electron-beam–plasma interaction that generates electron and ion cyclotron waves, namely proton and 4He cyclotron waves, whose dispersions are dependent on the magnetization parameter α = ω pe/Ωce and the temperature ratio τ = T e /T p . The background particles, e.g., 3He and 4He, resonate with the excited cyclotron waves and experience selective heating or acceleration. Specifically, the resonant modes of 3He ions lead to a more effective acceleration rate compared to those of the 4He ions. The simulation results provide a potential solution for understanding the abundance of heavy ions in the solar wind.

The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales.

A fast multi-dimensional magnetohydrodynamic formulation of the transition region adaptive conduction (TRAC) method

We have demonstrated that the transition region adaptive conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, successfully removing the influence of numerical resolution on the coronal density response to impulsive heating. This is achieved by adjusting the parallel thermal conductivity, radiative loss, and heating rates to broaden the transition region (TR), below a global cutoff temperature, so that the steep gradients are spatially resolved even when using coarse numerical grids. Implementing the original 1D formulation of TRAC in multi-dimensional magnetohydrodynamic (MHD) models would require tracing a large number of magnetic field lines at every time step in order to prescribe a global cutoff temperature to each field line. In this paper, we present a highly efficient formulation of the TRAC method for use in multi-dimensional MHD simulations, which does not rely on field line tracing. In the TR, adaptive local cutoff temperatures are used instead of global cutoff temperatures to broaden any unresolved parts of the atmosphere. These local cutoff temperatures are calculated using only local grid cell quantities, enabling the MHD extension of TRAC to efficiently account for the magnetic field evolution, without tracing field lines. Consistent with analytical predictions, we show that this approach successfully preserves the properties of the original TRAC method. In particular, the total radiative losses and heating remain conserved under the MHD formulation. Results from 2D MHD simulations of impulsive heating in unsheared and sheared arcades of coronal loops are also presented. These simulations benchmark the MHD TRAC method against a series of 1D models and demonstrate the versatility and robustness of the method in multi-dimensional magnetic fields. We show, for the first time, that pressure differences, generated during the evaporation phase of impulsive heating events, can produce current layers that are significantly narrower than the transverse energy deposition.

Physical and acoustic response of Pinus palustris to fire

Crackling sounds from burning vegetation provide information to fire-experienced land managers regarding the combustion process. These acoustic impulse events can inform practitioners of a variety of situations, from the type of vegetation involved and relative “dryness,” to alerting wildland fire fighters to increased burning along tree boles and in canopies. More recently, acoustic sampling has supported these observations by quantifying species and drought-stress specific differences in the acoustics impulse events in both the laboratory and field. Our team builds on this work by quantifying the response of long leaf pine (Pinus palustris) in grass-stage to low-intensity fire. We planted live fuel beds in Northern Florida with long leaf pine seedlings. We then used prepared dead long leaf pine needles to carry low-intensity fire past the live plants. Crackling sounds from both the live and dead needles were recorded. These acoustic impulse events were then analyzed to identify any unique characters associated with the live and dead needles. We pair these results with single leaf-cluster scale laboratory experiments in which we documented the mechanical and acoustic response along the axial extent of the leaves. We present the results of long leaf pine’s acoustic and mechanical response to low-intensity fire.

An analysis of angular directivity for small caliber firearm noise

Accurately describing the sound field generated by an impulsive source is non-trivial. Conventional methods for analyzing impulsive noise of firearms consists of deploying one or more circular microphone arrays centered on the muzzle of the source. Currently, much debate exists around the design of these microphone arrays (radius, quantity of sensors, angular spacing, etc.) and the resulting effect on capturing source directivity of the impulse event. An in-depth investigation of data collected on small caliber firearms operating in outdoor environments is performed with an emphasis on describing source directivity as a function of (1) array radius, (2) quantity of microphones, and (3) angular spacing. Ultimately, given a sufficient circular microphone array, the angular directivity of an impulsive source can be generalized using analytical curve fitting functions.

Development of parameter-based criteria for applying adjustment for highly impulsive sound sources

The paper presents the development of parameter-based criteria for application of the highly impulsive noise adjustment, which can be the extension to the approach described in standard ISO 1996-1:2016. All calculations in paper are based on the highly impulsive noise example - collision of the train cars. The research material was a record of data collected during two months of continuous noise monitoring, followed by statistical analysis of the subject. The classification based on the analysis of exposure levels was compared with the objective method proposed by the authors, based on the analysis of the distinctive characteristics of impulsive noise: impulsiveness of a given event and its rise time. As a result, three types of impulsive events: clear, masked and weak impulses were proposed with recommendation of criteria when to apply the impulsive adjustment in relation to time of a day.

Benefits of enhanced techniques combining negentropy, spectral correlation and kurtogram for bearing fault diagnosis

In condition monitoring based on vibrations for rotating machines fault detection, one of the typical symptoms is the presence of repetitive transients, which are characterized by impulsive and cyclostationarity signature. The approach quite popular nowadays in the industry for their detection is time–frequency techniques. Those techniques are mainly analysis tools instead of processing tools, and in any case, they are unable to offer a versatile methodology that applies to all mechanical signals in all circumstances. On the one hand, the paper is motivated by ideas borrowed from thermodynamics, where transients are seen as departures from a state of equilibrium; it is proposed to measure the negentropy of the squared envelope (SE) and the squared envelope spectrum (SES) of the signal. On the other hand, the paper proposes an adequate approach to exploit methods such as spectral correlation and kurtogram. The work’s main objective is to investigate connections in those approaches to capture the signature of this repetitive behavior. The methodology used in this paper proposes to display as images all three proposed techniques. The impulsive events are then detected and localized in frequency by high values of the squared envelope spectrum (SES) infogram in some frequency bands. In order to analyze the signal in the frequency domain, the Short-Time Fourier Transform (STFT) is then used. The STFT is suggested in this study due to its simplicity and high flexibility. For fault, such as bearings, Kurtogram was demonstrated to be efficient. However, kurtosis based on temporal signals is effective under some conditions; its performance is low in the presence of a low signal-to-noise ratio. The paper analyzed the case of Ball Pass Frequency Inner Race (BPFI), where bearings are housed in a casing allowing the shaft to rotate while driven by a variable speed electric motor. A radial load is applied using a hydraulic cylinder, and different sizes of defects are realized. For fault like BPFI, the negentropy gives more information even for a shallow size of fault and allows a prompt fault detection, and it can also be used for fault localization. The paper demonstrated that results obtained from negentropy through infograms combining with spectral correlation could significantly extend the domain of the applicability of the Kurtogram.

Associations between non-suicidal self-injury and negative romantic relationship life events in male justice-involved adolescents

BackgroundIn the current study we investigated impulsivity and negative life events in relation to non-suicidal self-injury (NSSI) in correctional settings.MethodsA total of 141 male justice-involved juveniles participated in our cross-sectional study, aged between 14 and 21 years old (M = 17.75; SD = 1.38). Data collection took place in correctional institutions in Hungary. A binary logistic regression was conducted to investigate possible associations between NSSI, impulsivity and negative life events.ResultsLifetime prevalence of NSSI was 53.9% (N = 76). In a binary logistic regression model, only negative romantic relationship events were significantly associated with the risk of current NSSI (OR = 1.29; 95% CI = [1.06–1.56]). Other types of negative life events (family-related, friendship-related), impulsivity, age and conviction status did not have a significant role in the model.ConclusionsThe results suggest that juvenile offenders should receive additional support to manage stress that is associated with negative life events, especially problems in romantic relationships. It is essential to help young inmates to find an adaptive way of reducing stress caused by negative relationship life events.

The Evolution of Research on Abundances of Solar Energetic Particles

Sixty years of study of energetic particle abundances have made a major contribution to our understanding of the physics of solar energetic particles (SEPs) or solar cosmic rays. An early surprise was the observation in small SEP events of huge enhancements in the isotope 3He from resonant wave–particle interactions, and the subsequent observation of accompanying enhancements of heavy ions, later found to increase 1000-fold as a steep power of the mass-to-charge ratio A/Q, right across the elements from H to Pb. These “impulsive” SEP events have been related to magnetic reconnection on open field lines in solar jets; similar processes occur on closed loops in flares, but those SEPs are trapped and dissipate their energy in heat and light. After early controversy, it was established that particles in the large “gradual” SEP events are accelerated at shock waves driven by wide, fast coronal mass ejections (CMEs) that expand broadly. On average, gradual SEP events give us a measure of element abundances in the solar corona, which differ from those in the photosphere as a classic function of the first ionization potential (FIP) of the elements, distinguishing ions and neutrals. Departures from the average in gradual SEPs are also power laws in A/Q, and fits of this dependence can determine Q values and thus estimate source plasma temperatures. Complications arise when shock waves reaccelerate residual ions from the impulsive events, but excess protons and the extent of abundance variations help to resolve these processes. Yet, specific questions about SEP abundances remain.

Hydrodynamics of Small Transient Brightenings in the Solar Corona

Abstract Small scale transients occur in the solar corona at much higher frequencies than flares and play a significant role in coronal dynamics. Here we study three well-identified transients discovered by Hi-C and also detected by the EUV channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We use 0D enthalpy-based hydrodynamical simulations and produce synthetic light curves to compare with AIA observations. We have modeled these transients as loops of ∼1.0 Mm length depositing energies ∼1023 erg in ∼50 s. The simulated synthetic light curves show reasonable agreement with the observed light curves. During the initial phase, conduction flux from the corona dominates over the radiation, like impulsive flaring events. Our results further show that the time-integrated net enthalpy flux is positive, hence into the corona. The fact that we can model the observed light curves of these transients reasonably well by using the same physics as those for nanoflares, microflares, and large flares, suggests that these transients may have a common origin.

Combined Optical and Radio‐Frequency Measurements of a Lightning Megaflash by the FORTE Satellite

AbstractThe optical and VHF instrumentation on the fast on‐orbit recording of transient events (FORTE) satellite is used to document the combined phenomenology evolution of a lightning “megaflash”—Mesoscale lightning that propagates laterally over exceptional distances. We identify a FORTE flash whose maximum extent was 82 km and inferred length over multiple distinct branches exceeded 100 km. This flash lasted 1.2 s and produced 250 optical and 591 radio frequency events. We find that the channel development mapped by FORTE's pixelated lightning imager (LLS) occurred at a typical speed of 2.6 × 105 m s−1 and was accompanied by sustained periods of VHF emission that could individually exceed 100 ms in duration. The impulsive IC events generated by the flash indicate that this development occurred at altitudes between 3 and 8 km. Four +CG strokes were identified in the VHF waveform data that are responsible for two of the three highly radiant LLS groups (two of the +CGs were not as optically bright as the others). These strokes occurred at different locations throughout the flash footprint with the most distant strokes separated by approximately 50 km. These space‐based observations match previous observations of megaflashes as well as ground‐based measurements of negative leader development during “spider” lightning, suggesting that FORTE is sensing the same phenomena.