The interaction of a solar wind discontinuity with the backstreaming particles of the Earth’s ion foreshock can generate hot, tenuous plasma transients such as foreshock bubbles (FB) and hot flow anomalies (HFA). These transients are known to have strong effects on the magnetosphere, distorting the magnetopause (MP), either locally during HFAs or globally during FBs. However, previous studies on the global impact of FBs have not been able to determine whether the response stems directly from the transverse scale size of the phenomenon or its fast motion over the magnetosphere. Here we present the observation of an FB and its impact on the magnetosphere from different spacecraft scattered over the dayside magnetosphere. We are able to constrain the size of the transverse scale of an FB from direct observations to be about 10 $R_\mathrm{E}$. We further suggest that a combination of this scale and the motion of the FB over the MP is responsible for the previously reported global response of the dayside magnetosphere.

During the first flyby of the BepiColombo composite spacecraft at Mercury in October 2021 ion spectrometers observed two intense spectral lines with energies between 10 and 70eV. The spectral lines persisted also at larger distances from Mercury and were ob- served again at lower intensity during cruise phase in March 2022 and at the second and third Mercury flyby as a single band. The ion composition indicates that water is the dominant gas source. The outgassing causes the composite spacecraft to charge up to a negative potential of up to -50V. The distribution and intensity of the lower energy signal depends on the intensity of low energy electron fluxes around the spacecraft which again depend on the magnetic field orientation. We interpret the observation as being caused by water outgassing from different source locations on the spacecraft being ion- ized in two different regions of the surrounding potential. The interpretation is confirmed by two dimensional particle-in-cell simulations.

Precipitation of auroral electrons is usually assumed to be symmetric with respect to the sign of the dawn-dusk (By) component of the interplanetary magnetic field (IMF). This is also the case in most currently used precipitation models, which parameterize solar wind driving by empirical coupling functions. However, recent studies have showed that geomagnetic activity is significantly modulated by the signs and amplitudes of IMF By and the Earth’s dipole tilt angle $\Psi$. This so called explicit By dependence is not yet included in any current precipitation models. In this paper, we quantify this By dependence for auroral electron precipitation for the first time. We use precipitation measurements of the Defense Meteorological Satellite Program (DMSP) Special Sensor J instruments from years 1995-2022. We show that the dawnside electron precipitation at energies 13.9-30 keV is greater at auroral latitudes for opposite signs of By and $\Psi$ in both hemispheres, while the dusk sector is mostly unaffected by By and $\Psi$. For energies below 6.5 keV the By dependence is strong poleward of the auroral oval in the summer hemisphere, also exhibiting a strong dawn-dusk asymmetry. We also show that By dependence of precipitation modulates ionospheric conductance, which has important implications for solar wind response of ionospheric currents.

We analyzed the contribution of electromagnetic ion cyclotron (EMIC) wave driven electron loss to a flux dropout event in September 2017. The evolution of electron phase space density (PSD) through the dropout showed the formation of a radially peaked PSD profile as electrons were lost at high L*, resembling distributions created by magnetopause shadowing. By comparing 2D Fokker Planck simulations of pitch angle diffusion to the observed change in PSD, we found that the μ and K of electron loss aligned with maximum scattering rates at dropout onset. We conclude that, during this dropout event, EMIC waves produced substantial electron loss. Because pitch angle diffusion occurred on closed drift paths near the last closed drift shell, no radial PSD minimum was observed. Therefore, the radial PSD gradients resembled solely magnetopause shadowing loss, even though the local pitch angle scattering produced electron losses of several orders of magnitude of the PSD.

The monthly mean sunspot number has been larger in June-July 2023 than the double peak of solar cycle 24 (146 in February 2014 and 139 in November 2011) and brings us back to the sunspot level of solar cycle 23. However, the number of rocket launches, satellites in orbit and private space companies has increased dramatically in the past 20 years. Additionally, there is a growing interest for space exploration beyond Earth’s orbit, to the Moon and beyond, which comes with higher risk of being affected by space weather. Here, we discuss some of these trends and the role of the journal to improve awareness of space weather impacts.

The turbulent foreshock region upstream of the quasi-parallel bow shock is dominated by waves and reflected particles that interact with each other and create a large number of different foreshock transients. The structures with the enhanced magnetic field (Short Large Amplitude Magnetic Structures, SLAMS) and density spikes named plasmoids are frequently observed. They are one of the suggested sources of transient flux enhancements (TFE) or jets in the magnetosheath. Using measurements of the Magnetospheric Multiscale Spacecraft (MMS) and OMNI solar wind database between the 2015 and 2018 years, we have found that there is a category of events exhibiting both magnetic field and density enhancements simultaneously and we introduce the term “mixed structures” for them. Consequently, we divided our set of observations into three groups of events and present their comparative statistical analysis in the subsolar foreshock. Based on our results and previous research, we discuss the properties, possible origin and occurrence rates these events under different upstream conditions and their possible relation to the jet and plasmoid formation in the magnetosheath.

A document by Aryav Bhesania. Click on the document to view its contents.

High-Intensity Long-Duration Continuous AE Activity (HILDCAA) intervals are driven by High Speed solar wind Streams (HSSs) during which the rapidly-varying interplanetary magnetic field (IMF) produces high but intermittent dayside reconnection rates. This results in several days of large, quasi-periodic enhancements in the auroral electrojet (AE) index. There has been debate over whether the enhancements in AE are produced by substorms or whether HILDCAAs represent a distinct class of magnetospheric dynamics. We investigate sixteen HILDCAA events using the expanding/contracting polar cap model as a framework to understand the magnetospheric dynamics occurring during HSSs. Each HILDCAA onset shows variations in open magnetic flux, dayside and nightside reconnection rates, the cross-polar cap potential, and AL that are characteristic of substorms. The enhancements in AE are produced by activity in the pre-midnight sector, which is the typical substorm onset region. The periodicities present in the intermittent IMF determine the exact nature of the activity, producing a range of behaviours from a sequence of isolated substorms, through substorms which merge into one-another, to almost continuous geomagnetic activity. The magnitude of magnetic fluctuations, $dB/dt$, in the pre-midnight sector during HSSs is sufficient to produce a significant risk of Geomagnetically Induced Currents, which can be detrimental to power-grids and pipelines.

The aurora often appears as an approximately oval shape surrounding the magnetic poles, and is a visible manifestation of the intricate coupling between the Earth’s upper atmosphere and the near-Earth space environment. While the average size of the auroral oval increases with geomagnetic activity, the instantaneous shape and size of the aurora is highly dynamic. The identification of auroral boundaries holds significant value in space physics, as it serves to define and differentiate regions within the magnetosphere connected to the aurora by magnetic field lines. In this work, we demonstrate a method to detect and model the poleward and equatorward boundaries in global UV images. Our methodology enables analysis of the spatiotemporal variation in auroral boundaries from 2.5 years of UV imagery from the IMAGE satellite. The resulting dataset reveals a root mean square boundary normal velocity of 149 m/s for the poleward boundary and 96 m/s for the equatorward boundary and the velocities are shown to be stronger on the nightside than on the dayside. Interestingly, our findings demonstrate an absence of correlation between the amount of open magnetic flux and the amount of flux enclosed within the auroral oval. Furthermore, we highlight the inadequacy of a simplistic generalization of the expanding-contracting polar cap paradigm in explaining temporal variations in the auroral oval area, underscoring the imperative for an enhanced understanding of equatorward boundary fluctuations.

The random amplitude and phase fluctuations observed in trans-ionospheric radio signals are caused by the presence of electron density irregularities in the ionosphere. Ground-based measurements of radio wave signals provide information about the medium through which these signals propagate. The Canadian High Arctic Ionospheric Network (CHAIN) Global Position System (GPS) receivers record radio signals emitted by the GPS satellites, enabling the study of their spectral characteristics.This study presents examples of phase spectra with two power-law components. These components exhibit steeper spectral slopes at higher frequencies and shallower ones at lower frequencies. In most cases, the breaking frequency point is statistically larger than the frequency associated with the Fresnel scale under the Taylor hypothesis. To be more specific, we conducted a spectral characterization of sixty (60) events recorded by the CHAIN Churchill GPS receiver, which is located in the auroral oval. When fluctuations above the background level are only observed in the phase, the spectra tend to be systematically steeper. Conversely, the power increase in higher frequency fluctuations accompanying amplitude scintillation tends to result in shallower spectra. A basic yet powerful model of radio wave propagation through a turbulent ionosphere, characterized by a power law electron density spectrum, can help to explain the two power laws observed in the scintillation events presented in this study by identifying the role played by small-scale ionospheric irregularities in diffraction.

At Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, except for Ganymede, they have been only remotely detected, using ground-based radio-telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the range of magnetic flux tubes which sustain the various Jupiter-satellite interactions, and in turn to sample in situ the associated radio emission regions. In this study, we focus on the detection and the characterization of radio sources associated with Io, Europa and Ganymede. Using electric wave measurements or radio observations (Juno/Waves), in situ electron measurements (Juno/JADE-E), and magnetic field measurements (Juno/MAG) we demonstrate that the Cyclotron Maser Instability (CMI) driven by a loss-cone electron distribution function is responsible for the encountered radio sources. We confirmed that radio emissions are associated with Main (MAW) or Reflected Alfvén Wing (RAW), but also show that for Europa and Ganymede, induced radio emissions are associated with Transhemispheric Electron Beam (TEB). For each traversed radio source, we determine the latitudinal extension, the CMI-resonant electron energy, and the bandwidth of the emission. We show that the presence of Alfvén perturbations and downward field aligned currents are necessary for the radio emissions to be amplified.

A document by Corentin Louis. Click on the document to view its contents.

The outer areas of Jupiter and Saturn have multiple zonal winds, reaching the high latitudes, that penetrate deep into the planets' interiors, as suggested by gravity measurements. These characteristics are finally replicable in numerical simulations by including both a shallow stably stratified layer, below a convecting envelope, and increasing electrical conductivity. A dipolar magnetic field, assumed to be generated by a dynamo below our model, is imposed. We find that the winds' depth into the stratified layer depends on the local product of the squared magnetic field strength and electrical conductivity. The key for the drop-off of the zonal winds is a meridional circulation which perturbs the density structure in the stable layer. In the stable region its dynamics is governed by a balance between Coriolis and electromagnetic forces. Our models suggest that a stable layer extending into weakly conducting regions could account for the observed deep zonal wind structures.

Juno flew by Europa at an altitude of 355 km on 29 September, day 272, 2022. As one of Juno’s in situ science instruments, the Waves instrument obtained observations of plasma waves that are essential contributors to Europa’s interaction with its environment. Juno observed chorus, a band at the upper hybrid frequency providing the local plasma density, and electrostatic solitary structures in the wake. In addition, impulses due to micron-sized dust impacts on Juno were recorded with a local maximum very close to Europa. The peak electron density near Europa was $\sim$ 330 cm$^{-3}$ while the surrounding magnetospheric density was in the range of 50 to 150 cm$^{-3}$. There was a significant separation between the Europa flyby and Juno’s crossing of Jupiter’s magnetic equator, enabling a unique identification of effects associated with the moon as opposed to magnetospheric phenomena normally occurring at the magnetic equator near 10 Jovian radii.

The two most important wave modes responsible for energetic electron scattering to the Earth’s ionosphere are electromagnetic ion cyclotron (EMIC) waves and whistler-mode waves. In this study, we report direct observations of energetic electron (from 50 keV to 2.5 MeV) scattering driven by the combined effect of whistler-mode and EMIC waves using ELFIN measurements. We analyze several events exhibiting such properties, and show that electron resonant interactions with whistler-mode waves may enhance relativistic electron precipitation by EMIC waves. During a prototypical event which benefits from conjugate THEMIS measurements, we demonstrate that below the minimum resonance energy (Emin) of EMIC waves, the whistler-mode wave may both scatter electrons into the loss-cone and also accelerate them to higher energy (1-3 MeV). These accelerated electrons above Emin resonate with EMIC waves that, in turn, quickly scatter those electrons into the loss-cone. This enhances relativistic electron precipitation beyond what EMIC waves alone could achieve.

IntroductionOn the 19th of October, 2017, an interstellar object was detected by scientists for the first time¹. Called ‘Oumuamua, many factors about this foreign object were of high interest to the scientific community. This includes the fact that it was highly elongated, with theories on its shape ranging from it being shaped like a long cigar with a 10:1 ratio of height/ length, to it being unbelievably wide and thin as a millimeter². Another anomaly connected to the interstellar object was that it was able to achieve non-gravitational acceleration despite the fact that it was not a comet. It is decidedly not a comet due to its lack of a tail and no obvious star system of origin². This raised the question of ‘Oumuamua’s makeup to the scientific community as they attempted to understand how such anomalies could have occurred. One idea was that the object could have been an asteroid made of a highly porous material that gave the object a mean density much lighter than air³. Another idea is that the object was a large chunk of frozen hydrogen⁴. Some even made the assertion that the object was an artificially made solar sail created by interstellar intelligence². All these ideas have flaws in some ways, as both porous material and hydrogen ice would lose much structure upon being too close to the sun, and there has never as of yet been any evidence to suggest that life can come into existence at all beyond Earth, let alone life with the ability and will to create interstellar objects. One idea that therefore seems much more viable is the idea by Desch and Jackson, where they considered the possibility that ‘Oumuamua was a piece of an exo-planet similar to Pluto, that was rich in N2 ice⁵. This would allow the object to experience non-gravitational acceleration via outgassing from the heat of the sun. It would also explain the strange shape as melting from the sun on one side of the chunk could have been the cause of uneven ice removal. Overall this theory makes much sense as an explanation regarding the anomalies present in the object, however, Desch and Jackson’s backing of the statistical likeliness of this nitrogen iceberg appearing within our solar system is based upon the presumption that our planetary system is “typical” compared to others⁶. This may not be true. This is of high importance to the applicability of Desch and Jackson’s paper as they assert the idea that in order for a piece of a Pluto-like exoplanet to reach interstellar space and therefore have a high likeliness of reaching our solar system, an exoplanet similar in distance from its star to Neptune would need to exist so that objects within an “exo-Kuiper Belt” would have their orbits fully disturbed enough for ejection⁶. This study seeks to understand if the existence of planets as far away as Neptune exist to a large enough degree throughout the universe that the expulsion of fragments similar to the proposed nitrogen ice model of ‘Oumuamua from other systems is as likely as Desch and Jackson assert.

CONTEXT: The complex interplay between the Solar Wind and the lunar surface serves as a quintessential example of space weathering. However, uncertainties persist regarding the influence of plasma originating from Earth’s ionosphere, necessitating a comprehensive understanding of its quantitative impact. Hitherto, the dearth of reliable models has impeded accurate computation of ion flux from Earth to the Moon under varying solar wind conditions. AIM: The objective of this study is to adapt a kinetic model for the challenging conditions of having both the Earth and the Moon in a single simulation box. METHODS: IAPIC, the Particle-In-Cell Electromagnetic Relativistic Global Model was modified to handle the Sun-Earth-Moon system. It employs kinetic simulation techniques that have proven invaluable tools for exploring the intricate dynamics of physical systems across various scales while minimizing the loss of crucial physics information such as backscattering. RESULTS: The modeling allowed to derive the shape and size of the Earth’s magnetosphere and allowed tracking the O+ and H+ ions escaping from the ionosphere to the Moon: O+ tends to escape towards the dayside magnetopause, while H+ travels deeper into the magnetotail, extending up to the Lunar surface. In addition, plasma temperature anisotropy and backstreaming ions were simulated, allowing for future comparison with the experiment. CONCLUSION: This study shows how a kinetic model can successfully be applied to study the transport of ions in the Earth-Moon environment. A second paper will detail the effect on the Lunar environment and the impact on the Lunar water.

A document by Olusegun Jonah. Click on the document to view its contents.

Understanding local loss processes in Earth’s radiation belts is critical to understanding their overall structure. Electromagnetic ion cyclotron waves can cause rapid loss of multi-MeV electrons in the radiation belts and contribute to an uncommon three-belt structure in the radiation belts. These loss effects have been observed at a range of L* values, recently as low as L* = 3.5. Here, we present a case study of an event where a local minimum develops in multi-MeV electron phase space density near L* = 3.5 and evaluate the possibility of EMIC waves in contributing to the observed loss feature. Signatures of EMIC waves are shown including rapid local loss and pitch angle bite outs. Analysis of the wave power spectral density during event shows EMIC wave occurrence at higher L* values. Using these representative wave parameters, we calculate minimum resonant energies, diffusion coefficients, and simulate the evolution of electron PSD during this event. From these results, we find that O+ band EMIC waves could be contributing to the local loss feature during this event. O+ band EMIC waves are uncommon, but do occur in these L* ranges, and therefore may be a significant driver of radiation belt dynamics under certain preconditioning of the radiation belts.

A document by Tae Kim. Click on the document to view its contents.

We present new analysis methods of 3D MHD output data from the Space Weather Modeling Framework during a simulated storm event. Earth’s magnetosphere is identified in the simulation domain and divided based on magnetic topology and the bounding magnetopause definition. Volume energy contents and surface energy fluxes are analyzed for each subregion to track the energy transport in the system as the driving solar wind conditions change. Two energy pathways are revealed, one external and one internal. The external pathway between the magnetosheath and magnetosphere has magnetic energy flux entering the lobes and escaping through the closed field region and is consistent with previous work and theory. The internal pathway, which has never been studied in this manner, reveals magnetically dominated energy recirculating between open and closed field lines. The energy enters the lobes across the dayside magnetospheric cusps and escapes the lobes through the nightside plasmasheet boundary layer. This internal circulation directly controls the energy content in the lobes and the partitioning of the total energy between lobes and closed field line regions. Qualitative analysis of four-field junction neighborhoods indicate the internal circulation pathway is controlled via the reconnection X-line(s), and by extension, the IMF orientation. These results allow us to make clear and quantifiable arguments about the energy dynamics of Earth’s magnetosphere, and the role of the lobes as an expandable reservoir that cannot retain energy for long periods of time but can grow and shrink in energy content due to mismatch between incoming and outgoing energy flux.

The concepts underlying the Lorentz transform for time dilation and length contraction are presented. The notion of a rest frame is introduced and its usefulness discussed. The rest frame of the CMB (the Hubble frame) is proposed as the correct candidate for the rest frame in the Lorentz transform, and an equation developed to compute the relative time dilation between inertial frames based on this assumption.

A document by Niklas Grimmich. Click on the document to view its contents.

We investigate the role of auroral particle precipitation in small-scale (below hundreds of meters) plasma structuring in the auroral ionosphere over the Arctic. To the scope, we together analyse data recorded by an Ionospheric Scintillation Monitor Receiver (ISMR) of Global Navigation Satellite System (GNSS) signals and by an All-Sky Camera located in Longyearbyen, Svalbard (Norway). We leverage on the raw GNSS samples provided at 50 Hz by the ISMR to evaluate amplitude and phase scintillation indices at 1 s time resolution and the Ionosphere-Free Linear Combination at 20 ms time resolution. The simultaneous use of the 1 s GNSS-based scintillation indices allows identifying the scale size of the irregularities involved in plasma structuring in the range of small (up to few hundreds of meters) and medium-scale size ranges (up to few kilometers) for GNSS frequencies and observational geometry. Additionally, they allow identifying the diffractive and refractive nature of the found fluctuations on the recorded GNSS signals. Six strong auroral events and their effects on plasma structuring are studied. Plasma structuring down to scales of hundreds of meters are seen when strong gradients in auroral emissions at 557.7 nm cross the line of sight between the GNSS satellite and receiver. Local magnetic field measurements confirm small-scale structuring processes coinciding with intensification of ionospheric currents. Since 557.7 nm emissions primarily originate from the ionospheric E-region, plasma instabilities from particle precipitation at E-region altitudes are considered to be responsible for the signatures of small-scale plasma structuring highlighted in the GNSS scintillation data.