Energetic Fluxes Research Articles

Hydrogen bombardment-induced nano blisters in multilayered Mo/Si coatings

Nanometer-thick multilayered Mo/Si coatings, employed as artificial Bragg structures, are essential for reflecting specific wavelengths of light in synchrotrons, space telescopes, and extreme ultraviolet optical systems. However, these coatings are prone to blistering failures when exposed to energetic fluxes, such as hydrogen bombardment and solar wind particles. The blistering mechanism is investigated through systematic analysis of experimental data and the development of a multilayered mechanical model based on pockets of energy concentration theory. Energy release rates for pure mode fracture at blister tips, the evolution of blister morphologies, and interface fracture toughness are assessed through theoretical derivations. The relationship between blister radii and heights is elucidated and quantitatively validated against experimental data. Variations in fracture toughness are correlated to hydrogen characteristics, and the influence of hydrogen species, exposure temperature, dose, energy, and strained layer thickness on blister formation is evaluated using the developed model. These findings provide crucial insights for optimizing exposure parameters to mitigate blistering and enhance the performance and reliability of multilayered Mo/Si coatings.

Whistler wave scattering of energetic electrons past 90°

The consequences of a 90° barrier in the scattering of energetic electrons by whistler waves are explored with self-consistent two-dimensional particle-in-cell simulations. In the presence of a 90° scattering barrier, a field-aligned heat flux of energetic electrons will rapidly scatter to form a uniform distribution with pitch angles 0<θ<90° but with a discontinuous jump at θ=90° to a lower energy distribution of electrons with 90°<θ<180°. However, simulations reveal that such a distribution contains a large reservoir of free energy that is released to drive large-amplitude, oblique-propagating whistler waves (δB/B0∼0.1). As a result, energetic electrons near a pitch angle 90° experience strong resonance scattering. Nearly half of the energetic electrons in the positive parallel velocity plane cross the 90° barrier and diffuse to negative parallel velocities. Thus, the late-time electron velocity distribution becomes nearly isotropic. This result has implications for understanding the regulation of energetic particle heat flux in space and astrophysical environments, including the solar corona, the solar wind, and the intracluster medium of galaxy clusters.

Energy spectra of energetic neutral hydrogen backscattered and sputtered from the lunar regolith by the solar wind

Context. The solar wind impinging on the lunar surface results in the emission of energetic neutral atoms. This particle population is one of the sources of the lunar exosphere. Aims. We present a semi-empirical model to describe the energy spectra of the neutral emitted atoms. Methods. We used data from the Advanced Small Analyzer for Neutrals (ASAN) on board the Yutu-2 rover of the Chang’E-4 mission to calculate high-resolution average energy spectra of the energetic neutral hydrogen flux from the surface. We then constructed a semi-empirical model to describe these spectra. Results. Excellent agreement between the model and the observed energetic neutral hydrogen data was achieved. The model is also suitable for describing heavier neutral species emitted from the surface. Conclusions. A semi-analytical model describing the energy spectrum of energetic neutral atoms emitted from the lunar surface has been developed and validated by data obtained from the lunar surface.

Exploring the hardness of the ionising radiation with the infrared softness diagram

Aims. We explored the softness parameter in the infrared, ηIR′, whose main purpose is the characterisation of the hardness of the incident ionising radiation in emission-line nebulae. This parameter is obtained from the combination of mid-infrared wavelength range transitions corresponding to consecutive ionisation stages in star-forming regions. Methods. We compiled observational data from a sample of star-forming galaxies (SFGs), including luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs), to study the ηIR′ and its equivalent expression in two dimensions, the softness diagram. We compared them with predictions from photoionisation models to determine the shape of the ionising continuum energy distribution in each case. We also used the measured emission-line ratios as input for HCMISTRY-TEFF-IR, a code that performs a Bayesian-like comparison with photoionisation model predictions in order to quantify the equivalent effective temperature (T*) and the ionisation parameter. Results. We found similar average values within the errors of ηIR′ in (U)LIRGs (−0.57) in the rest of the SFGs (−0.51), which could be interpreted as indicative of a similar incident radiation field. This result is confirmed from the analysis using HCM-TEFF-IR, which simultaneously points to a slightly lower, although similar within the errors, T* scale for (U)LIRGs, even when a higher dust-to-gas mass ratio is considered in the models for these objects. These derived T* values are compatible with the ionisation from massive stars, without any need of harder ionising sources, both for (U)LIRGs and the rest of the SFGs. However, the derived T* in (U)LIRGs do not show any correlation with metallicity. This could be interpreted as a sign that their similar average T* values are due to the attenuation of the energetic incident flux from massive stars by the heated dust mixed with the gas. This is supported by the known very large amounts of small grains associated with the very high star formation rates measured in galaxies of this type.

Compatible alternative energy storage systems for electric vehicles: Review of relevant technology derived from conventional systems

Because of the energy crisis and environmental challenges, it is important to establish a new smart city model to offer some effective solutions. Electric vehicles are one of the primary components that may help to reduce environmental issues and intervene in the energy recovery and management process. On-board the vehicle, many methods can be used to manage the energetic flux. Hybrid arrangements are one of the strongest ways to merge two options. Arrangements can incorporate more than two separate energy sources, with the vehicle using one or both of them. Renewable energy advances these systems and provides new potential for the widespread use of hybrid and pure electric vehicles. The dynamic nature of the field, which includes varied technologies critical for renewable energy integration, justifies energy storage and recovery strategies. Its significance arises from its role in leading future research, informing policy decisions, and encouraging sustainability in energy practices across multiple industries. This work contributes to the development of robust and efficient energy infrastructures by addressing existing difficulties and optimizing energy systems. Generally, we will look at some existing energy storage methods that provide needed energy in electric vehicles. Some vehicles already employ these conventional technologies, so we will present some industry examples. And discuss the alternatives generated from these conventional techniques based on the most recent research on this subject. Energy recovery systems are also being considered as a supply system to increase range and support energy storage systems in a variety of configurations.

Heat Budget of Sub-Mediterranean Downy Oak Landscapes of Southeastern Crimea

This article presents the findings of a research endeavor focused on the diurnal and seasonal dynamics of heat balance and its constituent elements within an oak forest situated in the expanse of the Karadag Nature Reserve. Computed are the values corresponding to the elements of heat balance, encompassing radiation balance, latent heat fluxes corresponding to heat consumption for evaporation, turbulent heat exchange transpiring within the atmosphere, and heat flux coursing through the soil. The features of changes in the heat balance in two key areas are considered: in the zone of growth of the downy oak forest in an open area and in the forest itself. The study discloses patterns characterizing the apportionment of radiation balance into heat and energetic fluxes within the context of the downy oak landscapes native to the southeastern Crimea. Scrutiny of the data established that a substantial proportion of radiation balance finds application in propelling turbulent heat flux, while a minor share is channeled into processes of evaporation and soil heat flux. Evidenced is that the magnitudes of heat balance components, encompassing radiation balance, latent heat fluxes corresponding to heat consumption for evaporation, turbulent heat exchange transpiring within the atmosphere, and heat flux through the soil within the sub-canopy realm, undergo modifications contingent upon the seasons of the year and the vegetative phases of the downy oak forest. The correlation between air temperature and the constituents of heat balance is subject to analysis both within the confines of the territory in the zone of growth of the downy oak forest in an open area and in the forest itself. Manifest is the constancy of the influence exerted by forest vegetation upon heat balance; nevertheless, the degree of its impact is circumscribed by the cyclical dynamics of foliage upon the trees: a well-developed canopy serves to amplify the influence exerted upon the distribution of heat and energetic fluxes. This study of heat balance and its constituents assumes significance in engendering comprehension regarding the operation of downy oak landscapes that are situated on the periphery of their habitudinal range. Also, it helps to reveal deeper patterns of climate change in forest ecosystems.

Parametrization of Energetic Ion and Electron Fluxes in the Near‐Earth Magnetotail

AbstractThe near‐Earth plasma sheet region is the main source of energetic (tens to hundreds keV) ion and electron populations transported by convection and injections into the inner magnetosphere. Energetic ions from the plasma sheet contribute to the ring current, whereas energetic electrons contribute to the radiation belt seed population for further acceleration to relativistic energies. Near‐Earth plasma sheet energetic fluxes have been traditionally used to set boundary conditions for radiation belt and ring current models. This study provides an empirical parametrization for ∼75 keV flux intensity as a function of the geomagnetic activity index auroral electrojet and the equatorial magnetic field Bz. Such parametrization includes the dynamic magnetic field configuration in the near‐Earth plasma sheet and may be merged with empirical magnetic field models. We also provide models extending this parametrization to the [20, 300] keV of electron energy range and [75, 300] keV of ion energy range. The parametrization is developed based on THEMIS and Geostationary Operational Environmental Satellite measurements, and verified by comparison with MMS measurements in the near‐Earth plasma sheet. This parametrization incorporates meso‐scale transient flux variations associated with Bz perturbations into ring current and radiation belt simulations.

Variation of Hydrogen Energetic Neutral Atom Flux in the Subsolar Magnetosheath as a Function of Solar Cycle

AbstractWe analyzed observations of energetic neutral atoms (ENAs) of hydrogen collected from the subsolar magnetosheath by the Interstellar Boundary Explorer (IBEX) in Solar Cycle 24. We looked for long‐term solar activity‐related variation and correlation between the H ENA flux and the solar wind parameters. The H ENA flux in the energy range from 0.5 to 6 keV increased during the maximum and declining phases of the solar cycle. This H ENA flux increase happened during a period of enhanced solar wind dynamic pressure observed at 1 au. We study the relation between the ENA flux and solar wind pressure in the subsolar magnetosheath and conclude that the increase in the ENA flux is a consequence of enhanced ENA production. It is because of the increased solar wind pressure during the declining phase of the solar activity that moved the subsolar magnetosheath earthward into a region of denser hydrogen geocorona, thus increasing the H ENA production. Furthermore, we report a positive correlation between the H ENA flux in the subsolar magnetosheath and the solar wind pressure for the first four energy steps observed by IBEX‐Hi and a decrease for the highest energy acquired, which indicates the presence of a different parent ion population for those ENAs from that of the core solar wind. Our study also shows that the ENA flux correlates differently with the solar wind density and speed as a function of increasing energy of ENAs.

Understanding photochemical adaptations of microalgal ammonium extremophiles to elevated ammonium concentrations in abattoir anaerobic digestate

Identifying microalgal species with outstanding environmental resistance to NH4+ toxicity is critical to developing effective algal-based anaerobic effluent treatment. This is the case for two microalgal NH4+ extremophiles, Chlorella sp. MUR269 and Scenedesmus sp. MUR270 well suited to treat high nitrogen digestates. However, their exact tolerance mechanisms to high NH4+ conditions still need to be understood. A chlorophyll fluorescence approach based on high-throughput pulse amplitude-modulated fluorimetry was used to understand the photochemical adaptations of these species under increasing NH4+ concentrations (0, 100, 200 mgNL−1) derived from abattoir anaerobic digestate. Both species tolerated 200 mgN-NH4+L−1 in the digestate by exhibiting different photochemical mechanisms. Chlorella decreased its PSII primary photochemistry efficiency (Fq′/FM′) and maximum electron transport (rETRmax) immediately after exposure to the treatment conditions. In contrast, Scenedesmus maintained unaltered Fq′/FM′ regardless of NH4+-N concentration, while rETRmax was significantly reduced to a level of Chlorella at 200 mgNL−1. Energy transduction parameters showed Chlorella increased the size of its reaction centre antennae to capture more photons, which increased the trapping flux ratio and maintained efficient dissipation of excess energy. Conversely, Scenedesmus displayed reductions in the absorbed, trapped and dissipated energy fluxes, though its transported flux for photochemical energy production was similar to Chlorella sp. The energetic communication and connectivity between Chlorella PSII units went up by 47 % and 40 % when the NH4+-N level increased from 50 to 100 and N200 mgL−1, respectively, while Scenedesmus exhibited a dose-dependent decrease in the connectivity between its PSII components. The photosynthetic performance index revealed that the overall energetic flux processing efficiency by Scenedesmus was 86 % (50 mgNL−1), 73 % (100 mgNL−1) and 91 % (200 mgNL−1) higher than Chlorella sp. Thus, the two chlorophytes maintained their overall photochemical capacity by simple, economic biological mechanisms involving adjustments of antenna size and energetic communications between PSII neighbour units.

Adiabatic energy change in the inner heliosheath: how does it affect the distribution of pickup protons and energetic neutral atom fluxes?

ABSTRACT The hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to ∼5 and ∼20 times in the upwind and downwind directions at energies ∼1–2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.

Spherical Harmonic Representation of Energetic Neutral Atom Flux Components Observed by IBEX

The Interstellar Boundary Explorer (IBEX) images the heliosphere by observing energetic neutral atoms (ENAs). The IBEX-Hi instrument on board IBEX provides full-sky maps of ENA fluxes produced in the heliosphere and very local interstellar medium through charge exchange of suprathermal ions with interstellar neutral atoms. The first IBEX-Hi results showed that, in addition to the anticipated globally distributed flux (GDF), a narrow and bright emission from a circular region in the sky, dubbed the IBEX ribbon, is visible in all energy steps. While the GDF is mainly produced in the inner heliosheath, ample evidence indicates that the ribbon forms outside the heliopause in the regions where the interstellar magnetic field is perpendicular to the lines of sight. The IBEX maps produced by the mission team distribute the observations into 6° × 6° rectangle pixels in ecliptic coordinates. The overlap of the GDF and ribbon components complicates qualitative analyses of each source. Here, we find the spherical harmonic representation of the IBEX maps, separating the GDF and ribbon components. This representation describes the ENA flux components in the sky without relying on any pixelization scheme. Using this separation, we discuss the temporal evolution of each component over the solar cycle. We find that the GDF is characterized by larger spatial scale structures than those of the ribbon. However, we identify two isolated, small-scale signals in the GDF region that require further study.

Forecasting solar energetic proton integral fluxes with bi-directional long short-term memory neural networks

Solar energetic particles are mainly protons and originate from the Sun during solar flares or coronal shock waves. Forecasting the Solar Energetic Protons (SEP) flux is critical for several operational sectors, such as communication and navigation systems, space exploration missions, and aviation flights, as the hazardous radiation may endanger astronauts’, aviation crew, and passengers’ health, the delicate electronic components of satellites, space stations, and ground power stations. Therefore, the prediction of the SEP flux is of high importance to our lives and may help mitigate the negative impacts of one of the serious space weather transient phenomena on the near-Earth space environment. Numerous SEP prediction models are being developed with a variety of approaches, such as empirical models, probabilistic models, physics-based models, and AI-based models. In this work, we use the bidirectional long short-term memory (BiLSTM) neural network model architecture to train SEP forecasting models for three standard integral GOES channels (>10 MeV, >30 MeV, >60 MeV) with three forecast windows (1-day, 2-day, and 3-day ahead) based on daily data obtained from the OMNIWeb database from 1976 to 2019. As the SEP variability is modulated by the solar cycle, we select input parameters that capture the short-term, typically within a span of a few hours, and long-term, typically spanning several days, fluctuations in solar activity. We take the F10.7 index, the sunspot number, the time series of the logarithm of the X-ray flux, the solar wind speed, and the average strength of the interplanetary magnetic field as input parameters to our model. The results are validated with an out-of-sample testing set and benchmarked with other types of models.

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in Various Inner‐Magnetosphere Configurations at Geomagnetically Quiet Times

AbstractUtilizing multi‐point observations, we investigate a series of inner‐magnetosphere configurations formed at Kp ≤ 3+ when the magnetosphere‐ionosphere (M‐I) conjugate Abnormal Sub‐Auroral Ion Drifts (ASAID) developed near the plasmapause. We analyze the development of ASAID by adopting the recent theories of (1) fast‐time short‐circuiting explaining SAID development and (2) Larmor radius effects explaining ASAID development. The earthward ASAID electric field developed (1) by short‐circuiting when the reconnection‐related earthbound hot ring current (RC) electrons became stopped and ions kept moving earthward and started their usual Larmor rotations, and (2) because of the larger Larmor radius of the hot RC ions creating excess positive charges in the nearby cold‐inner‐edge plasmasheet plasma and deficit negative charges inside the hot RC region. Respective new findings include the observations of (1a) earthward hot RC ion injections across and near the ASAID channel in the inner magnetosphere and (1b) the localized increase of energetic proton differential fluxes (good proxy for hot RC ions) in the topside ionosphere within the ASAID channel, and (2a) M‐I conjugate ASAID and ASAID‐SAID series created by their respective single intrusion and repeated intrusions of hot RC ions into the cold plasmasheet plasma. New findings also include (3) the specifications of plasma waves such as Kelvin‐Helmholtz surface waves and electromagnetic ion cyclotron (EMIC) waves developed in the inner‐magnetosphere during plasmasheet rippling, and (4) the development of multiple ASAID channels in the hot zone impacted by EMIC waves.

Erratum for article: “Forecasting Solar Energetic Proton Integral Fluxes with Bi-Directional Long Short-Term Memory Neural Networks”

Erratum for article: “Forecasting Solar Energetic Proton Integral Fluxes with Bi-Directional Long Short-Term Memory Neural Networks”

Performance evaluation of SNB3GEO electrons flux forecasting model using LANL and GOES-13 observations

Energetic electrons in the outer radiation belt can damage the spacecrafts that operate within the region, such as geostationary satellites. For the purpose of terrestrial application, communications, broadcasting and metreological forecast, the existence of geostationary satellites are extremely useful. To provide alerts on the variations and enhancements of relativistic electron fluxes that can damage the spacecrafts, models which predict the relativistic electrons flux need to be accurate enough. In forecasting relativistic electron fluxes, SNB3GEO model provides relatively reliable and easily interpretable prediction output. Although the performance of this model was evaluated with respect to other models (such as Relativistic Electron Forecast Model (REFM)), its prediction accuracy never assessed with respect to experimental measurements except those used in model development (i.e. GOES-12, GOES-13). In this paper, we implemented evaluation of the prediction performance of SNB3GEO using two experimental measurements, which are LANL and GOES-13. The daily averaged relativistic electron flux data from 01 January 2013 to 31 December 2016 have been used to analyze the forecasting performance. Correlation Coefficient (CC), Normalized Root Mean Square Error (NRMSE) and Prediction Efficiency (PE) have been used as performance evaluation quantifier. The results indicated that SNB3GEO provides a more accurate forecast when it is compared with GOES-13 than LANL observations. The four years average values of CC,NRMSE and PE, when the model performance has been evaluated with observations of GOES-13 are 0.896,0.497 and 0.792, respectively, whereas the average values are CC=0.739,NRMSE=0.706 and PE=0.450, when the model performance evaluated with respect to observations of LANL. Such prediction performance evaluation of SNB3GEO will contribute for further improvement of the model used to predict energetic electrons fluxes in Earth’s outer radiation belt.

Contact effects by mitochondria: biological destruction of cultivated B16 – F10 melanoma cells

In recent years therapeutic effects produced by mitochondria, transplanted to pathogenic regions in an organism, which demonstrate their high migration activity and tropicity with respect to filling of energetic vacuum, have been inspiring a renewed interest in the scientific community. In this context, this raises the question of the source of metabolically active mitochondria and their histological compatibility required for the mitochondrial transplantation. Aim. The aim of our research work is to study characteristics/ quality of mitochondria from cells of the liver and the heart in rats, which in the in vitro system have produced their impact on different biological features of the B16-F10 murine melanoma cell culture. Materials and methods. In our research work we have used cells of the B16-F10 murine melanoma cell line culture. In the framework of the study, an experiment with mitochondria harvested from the liver and the heart of a rat has been conducted. Mitochondria have been isolated using differential centrifugation with a high-speed refrigerated centrifuge. With the B16-F10 culture cells, we have designed the following variants of our experiments: 1) use of cardiac mitochondria (1 mg/mL, in terms of total protein); 2) use of cardiac mitochondria (1 mg/mL) + succinic acid (10-4%); 3) mitochondria of the liver (1 mg/mL, in terms of total protein); 4) use of mitochondria of the liver (1 mg/mL) + succinic acid (10-4%); 5) use of succinic acid (10-4%) solely; 6) the reference specimen with no use of mitochondria and the above agents. An assessment of the impact made by mitochondria on the migration of the B16-F10 cells has been performed with the scratch wound healing test. For the purpose of an analysis of the effect produced by mitochondria on the energetic metabolism of the B16-F10 cell culture we have measured main parameters of the cell respiration and glycolysis in stress tests with adding some toxic chemicals. The rate of the cellular respiration has been assessed by measuring the amount of oxygen taken in (oxygen consumption rate, OCR), and the glycolysis level has been evaluated by the extracellular acidification rate (ECAR). Results. Adding cardiac and hepatic mitochondria to the cultivated B16-F10 cells has produced a pronounced cytopathic effect, which has become more remarkable upon expiration of two days of the cell cultivation and which has consisted in cytoplasm granulation and partial detaching of the cells. Introducing mitochondria of the heart to the cultivated B16-F10 cells has induced a considerable decrease both in the background-related and the maximum level of oxygen consumption by the B16-F10 cells as against the reference samples without adding of mitochondria. Adding the cardiac mitochondria has led to a statistically significant decrease in the base level of ECAR by 14,36 mpH/min (t = 3,12, df = 10) as compared with the reference values. Introducing hepatic mitochondria has also resulted in a reduction of the average value of ECAR as against the background by 4,8 mpH/min. Conclusion. Metabolically active mitochondria are capable of reformatting energetic fluxes in tumor cells and change their cellular respiration that leads to the most effectively realized death of the cultivated B16-F10 tumor cells.

Dissecting Flux Balances to Measure Energetic Costs in Cell Biology: Techniques and Challenges

Life is a nonequilibrium phenomenon: Metabolism provides a continuous supply of energy that drives nearly all cellular processes. However, very little is known about how much energy different cellular processes use, i.e., their energetic costs. The most direct experimental measurements of these costs involve modulating the activity of cellular processes and determining the resulting changes in energetic fluxes. In this review, we present a flux balance framework to aid in the design and interpretation of such experiments and discuss the challenges associated with measuring the relevant metabolic fluxes. We then describe selected techniques that enable measurement of these fluxes. Finally, we review prior experimental and theoretical work that has employed techniques from biochemistry and nonequilibrium physics to determine the energetic costs of cellular processes.

Oblique and rippled heliosphere structures from the Interstellar Boundary Explorer

Past analysis has shown that the heliosphere structure can be deduced from correlations between long-scale solar wind pressure evolution and energetic neutral atom emissions. However, this required spatial and temporal averaging that smoothed out small or dynamic features of the heliosphere. In late 2014, the solar wind dynamic pressure increased by roughly 50% over a period of 6 months, causing a time and directional-dependent rise in around 2–6 keV energetic neutral atom fluxes from the heliosphere observed by the Interstellar Boundary Explorer. Here, we use the 2014 pressure enhancement to provide a simultaneous derivation of the three-dimensional heliospheric termination shock (HTS) and heliopause (HP) distances at high resolution from Interstellar Boundary Explorer measurements. The analysis reveals rippled HTS and HP surfaces that are oblique with respect to the local interstellar medium upwind direction, with significant asymmetries in the heliosphere structure compared to steady-state heliosphere models. We estimate that the heliosphere boundaries contain roughly ten astronomical unit-sized spatial variations, with slightly larger variations on the HTS surface than the HP and a large-scale, southwards-directed obliquity of the surfaces in the meridional plane. Comparisons of the derived HTS and HP distances with Voyager observations indicate substantial differences in the heliosphere boundaries in the northern versus southern hemispheres and their motion over time.

Evidence of the Alfvén Transition Layer and Particle Precipitation in the Cusp Region: 3D Global PIC Simulation of the Solar Wind–Earth Magnetosphere Interaction

A transition layer, named the Alfvénic transition layer (or ATL), has been clearly evidenced near the outer boundary of the cusp by experimental observations from the Cluster mission. This layer characterized by a local value of Log M A ∼ 1, where M A is the Alfvén Mach number, allows the bulk flow to transit from super-Alfvénic to sub-Alfvénic from the exterior to the interior side of the outer cusp. The ATL has been observed during northward interplanetary magnetic field orientation, and mainly within the meridian plane. Currently, 3D Particle In Cell (PIC) global simulations of the solar wind–magnetosphere interaction are being performed in order to analyze the cusp region and this layer in detail. Present results stress the following points: (i) the ATL has a 3D structure; (ii) within the meridian plane, the ATL appears as a sublayer within a much more extended slow-mode pattern, and it is almost adjacent and located above the upper edge of the stagnant exterior cusp (SEC); and (iii) the plasma deceleration through the ATL is not uniform in the region located above the cusp. In addition, present preliminary results stress that (a) the spiraled streamlines of ion/electron fluxes converge when approaching the cusp, and their intensity strongly increases; and (b) ion and electron energetic fluxes penetrating the cusp region strongly differ in terms of their penetration depths and are issued from different regions of the magnetosphere/magnetosheath. Our results illustrate the importance of 3D effects used with a PIC simulation approach allowing the analysis of each population simultaneously.

Explanation of Heliospheric Energetic Neutral Atom Fluxes Observed by the Interstellar Boundary Explorer

Interstellar neutral atoms propagating into the heliosphere experience charge exchange with the supersonic solar wind (SW) plasma, generating ions that are picked up by the SW. These pickup ions (PUIs) constitute ∼25% of the proton number density by the time they reach the heliospheric termination shock (HTS). Preferential acceleration of PUIs at the HTS leads to a suprathermal, kappa-like PUI distribution in the heliosheath, which may be further heated in the heliosheath by traveling shocks or pressure waves. In this study, we utilize a dynamic, 3D magnetohydrodynamic model of the heliosphere to show that dynamic heating of PUIs at the HTS and in the inner heliosheath (IHS), as well as a background source of energetic neutral atoms (ENAs) from outside the heliopause, can explain the heliospheric ENA signal observed by the Interstellar Boundary Explorer (IBEX) in the Voyager 2 direction. We show that the PUI heating process at the HTS is characterized by a polytropic index larger than 5/3, likely ranging between γ ∼ 2.3 and 2.7, depending on the time in solar cycle 24 and SW conditions. The ENA fluxes at energies >1.5 keV show large-scale behavior in time with the solar cycle and SW dynamic pressure, whereas ENAs < 1.5 keV primarily exhibit random-like fluctuations associated with SW transients affecting the IHS. We find that ≲20% of the ENAs observed at ∼0.5–6 keV come from other sources, likely from outside the heliopause as secondary ENAs. This study offers the first model replication of the intensity and evolution of IBEX-Hi ENA observations from the outer heliosphere.