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We present measurements of 30–700 keV Solar Energetic Electrons (SEEs) near the Moon when within the terrestrial magnetotail by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft. Despite their detection deep within the tail, the incident flux and spectral shape of these electrons are nearly identical to measurements taken upstream of Earth in the solar wind by the Wind spacecraft; however, their pitch angle distribution is isotropized compared to the more field‐aligned distribution upstream. We illustrate that SEEs initially traveling Earthward precipitate onto the lunar far‐side, generating extended shadows in the cis‐lunar electron distribution. By modeling the dynamics of these electrons, we show that their precipitation patterns on the lunar near‐side are comparatively reduced. The non‐uniform precipitation and accessibility of potentially hazardous electrons to the Moon's surface are highly relevant in the context of astronaut safety during the planned exploration of the lunar environment. Plain Language Summary The Moon is located within the tail of Earth's magnetosphere during one‐third of its orbit. Although the strong terrestrial magnetic field prevents high‐energy particles from reaching Earth's surface, the Moon does not receive the same protection when it is within the terrestrial magnetotail. Instead, we show that the high‐energy electron flux near the Moon is unchanged during intense solar energetic electron events compared to measurements taken far upstream of Earth. However, the precipitation of these particles onto the lunar surface is non‐uniform. Since these electrons gain access to the magnetosphere from down‐tail of the Moon, they preferentially bombard the lunar far‐side surface. This creates a shadow in the electrons on the nearside that extends far beyond the Moon toward Earth. Hence, despite the high flux of these particles that are potentially hazardous to future activities on the lunar surface, there exist regions across the lunar near‐side where the relative flux of these electrons is reduced relative to the upstream value when the Moon is within the magnetotail. These findings provide context for the fundamental scientific understanding of high‐energy solar electrons and their access to the lunar surface. Key Points High‐energy solar energetic electrons (SEEs) have direct access to the lunar environment when in the terrestrial magnetotail Precipitation onto the lunar nightside carves‐out electrons from the ambient distribution, generating extended shadows far from the Moon When in the tail, the lunar surface is non‐uniformly bombarded by Earthward‐traveling SEEs, with reduced access to the dayside hemisphere

Using Bayesian analyses we study the solar electron density with the NANOGrav 11 yr pulsar timing array (PTA) data set. Our model of the solar wind is incorporated into a global fit starting from pulse times of arrival. We introduce new tools developed for this global fit, including analytic expressions for solar electron column densities and open source models for the solar wind that port into existing PTA software. We perform an ab initio recovery of various solar wind model parameters. We then demonstrate the richness of information about the solar electron density, n E , that can be gleaned from PTA data, including higher order corrections to the simple 1/r 2 model associated with a free-streaming wind (which are informative probes of coronal acceleration physics), quarterly binned measurements of n E and a continuous time-varying model for n E spanning approximately one solar cycle period. Finally, we discuss the importance of our model for chromatic noise mitigation in gravitational-wave analyses of pulsar timing data and the potential of developing synergies between sophisticated PTA solar electron density models and those developed by the solar physics community.

Solar Orbiter's four in situ instruments have recorded numerous energetic electron events at heliocentric distances between 0.5 and 1 au. We analyze energetic electron fluxes, spectra, pitch-angle distributions, associated Langmuir waves, and type III solar radio bursts for three events to understand what causes modifications in the electron flux and identify the origin and characteristics of features observed in the electron spectrum. We investigate what electron beam properties and solar wind conditions are associated with Langmuir wave growth and spectral breaks in the electron peak flux as a function of energy. We observe velocity dispersion and quasilinear relaxation in the electron flux caused by the resonant wave–particle interactions in the deca-keV range, at the energies at which we observe breaks in the electron spectrum, cotemporal with the local generation of Langmuir waves. We show, via the evolution of the electron flux at the time of the event, that these interactions are responsible for the spectral signatures observed around 10 and 50 keV, confirming the results of simulations by Kontar and Reid. These signatures are independent of pitch-angle scattering. Our findings highlight the importance of using overlapping FOVs when working with data from different sensors. In this work, we exploit observations from all in situ instruments to address, for the first time, how the energetic electron flux is modified by the beam–plasma interactions and results in specific feature appearing in the local spectrum. Our results, corroborated with numerical simulations, can be extended to a wider range of heliocentric distances.

Quantifying the energy content of accelerated electron beams during solar eruptive events is a key outstanding objective that must be constrained to refine particle acceleration models and understand the electron component of space weather. Previous estimations have used in situ measurements near the Earth, and consequently suffer from electron-beam propagation effects. In this study, we deduce properties of a rapid sequence of escaping electron beams that were accelerated during a solar flare on 2013 May 22 and produced type III radio bursts, including the first estimate of energy density from remote-sensing observations. We use extreme-ultraviolet observations to infer the magnetic structure of the source active region NOAA 11745, and Nançay Radioheliograph imaging spectroscopy to estimate the speed and origin of the escaping electron beams. Using the observationally deduced electron-beam properties from the type III bursts and cotemporal hard X-rays, we simulate electron-beam properties to estimate the electron number density and energy in the acceleration region. We find an electron density (above 30 keV) in the acceleration region of 102.5 cm−3 and an energy density of 2 × 10−5 erg cm−3. Radio observations suggest the particles travelled a very short distance before they began to produce radio emission, implying a radially narrow acceleration region. A short but plausibly wide slab-like acceleration volume of 1026–1028 cm3 atop the flaring loop arcade could contain a total energy of 1023–1025 erg (∼100 beams), which is comparable to energy estimates from previous studies.

Solar accelerated electron beams, a component of space weather, are emitted by eruptive events at the Sun. They interact with the ambient plasma to grow Langmuir waves, which subsequently produce radio emission, changing the electrons’ motion through space. Solar electron beam–plasma interactions are simulated using a quasilinear approach to kinetic theory to probe the variations in the maximum electron velocity [ Ξ ] responsible for Langmuir wave growth between the Sun’s surface and 50 R ⊙ above the surface. We find that it peaks at 5 R ⊙ at 0.38 c and decreases as r − 0.5 to 0.16 c at 50 R ⊙ . The role of the initial beam density [ n beam ] and velocity spectral index [ α ] on the energy density of the beam and Ξ is extensively studied. We show that a high spectral index yields a lower Ξ , while a high n beam yields a higher Ξ , and vice versa. We observe at different energy channels that below 60 keV, electrons arrive up to 0.75 minutes earlier than expected at 13 R ⊙ while higher energy electrons propagate scatter free in the plasma. A special focus on the associated Type III radio burst shows that the energy range [ Δ E ] of electrons producing Langmuir waves evolves from 7 keV to 1 keV between 0 and 28 R ⊙ . Understanding the transport effect on the electron beam kinetics and arrival time at Earth has space weather implications. The results of this simulation can be tested against readily available in-situ data from Solar Orbiter and Parker Solar Probe .

We report, for the first time, the impact of interplanetary coronal mass ejections (ICME) on the recently discovered O(1S) 557.7 nm dayglow emission in the Martian atmosphere. While there are a few studies on the seasonal variation of 557.7 nm dayglow emission available in the literature, the impact of ICME has not been investigated so far. Using the instruments aboard the ExoMars‐TGO and Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, we show that the primary emission peak (75–80 km) remains unaffected during ICME events compared to quiet‐times. However, an enhancement has been observed in the brightness of the secondary emission peak (110–120 km) and the upper altitude region (140–180 km). The enhancement is attributed to the increased solar electrons, X‐ray fluxes and Solar Energetic Particles, augmenting the electron‐impact processes causing the enhancement in the brightness. Thus, this study has an implication to the brightness of Martian upper atmosphere during intense solar transients like ICME. Plain Language Summary The O(1S) 557.7 nm dayglow emission has been recently discovered in the Martian dayside atmosphere, having a primary and secondary emission peak observed at ∼80 and ∼120 km altitudes, respectively. It is produced via photodissociation of CO2 by solar extreme ultraviolet radiation and electron impact processes. It is to be noted that space weather events like interplanetary coronal mass ejection (ICME) can significantly affect the Martian atmosphere. This motivates us to study the behavior of 557.7 nm emission during ICME events. This study reports, for the first time, the impact of ICME on the O(1S) 557.7 nm dayglow emission using the instruments onboard ExoMars‐TGO and MAVEN spacecrafts. Our findings show that during the ICME, the primary emission peak does not show any variation as compared to quiet‐times. However, the brightness of secondary emission peak and upper‐altitude region (140–180 km) show enhancements in comparison to quiet‐times. We have observed an increase in the solar X‐ray, electron fluxes and Solar Energetic Particles during the ICME events which produces more photoelectrons and secondary electrons. This enhances the electron impact process resulting in the enhancement in the brightness of the secondary emission peak and the upper altitude region. Key Points Impact of interplanetary coronal mass ejections (ICME) on the Martian 557.7 nm dayglow emission has been studied using instruments onboard ExoMars‐TGO and Mars Atmosphere and Volatile Evolution spacecrafts During ICMEs, the primary emission peak does not show variation compared to quiet‐time and seasonal quiet‐time average periods An enhancement in the secondary emission peak and upper altitude region (140–180 km) is observed due to increased electron impact process

We utilize observations from the Parker Solar Probe (PSP) to study the radial evolution of the solar wind in the inner heliosphere. We analyze electron velocity distribution functions observed by the Solar Wind Electrons, Alphas, and Protons suite to estimate the coronal electron temperature and the local electric potential in the solar wind. From the latter value and the local flow speed, we compute the asymptotic solar wind speed. We group the PSP observations by asymptotic speed, and characterize the radial evolution of the wind speed, electron temperature, and electric potential within each group. In agreement with previous work, we find that the electron temperature (both local and coronal) and the electric potential are anticorrelated with wind speed. This implies that the electron thermal pressure and the associated electric field can provide more net acceleration in the slow wind than in the fast wind. We then utilize the inferred coronal temperature and the extrapolated electric + gravitational potential to show that both electric field driven exospheric models and the equivalent thermally driven hydrodynamic models can explain the entire observed speed of the slowest solar wind streams. On the other hand, neither class of model can explain the observed speed of the faster solar wind streams, which thus require additional acceleration mechanisms.

A bstract We quantify the effects of light spin-zero particles with pseudoscalar couplings to leptons and scalar couplings to nucleons on the evolution of solar neutrinos. In this scenario the matter potential sourced by the nucleons in the Sun’s matter gives rise to spin precession of the relativistic neutrino ensemble. As such the effects in the solar observables are different if neutrinos are Dirac or Majorana particles. For Dirac neutrinos the spin-flavour precession results into left-handed neutrino to right-handed neutrino (i.e., active-sterile) oscillations, while for Majorana neutrinos it results into left-handed neutrino to right-handed antineutrino (i.e., active-active) oscillations. In both cases this leads to distortions in the solar neutrino spectrum which we use to derive constraints on the allowed values of the mediator mass and couplings via a global analysis of the solar neutrino data. In addition for Majorana neutrinos spin-flavour precession results into a potentially observable flux of solar electron antineutrinos at the Earth which we quantify and constrain with the existing bounds from Borexino and KamLAND.

Whether solar wind electrons expanding into the heliosphere can preserve information about their origin in the solar corona remains an open debate. The suprathermal strahl temperature has often been postulated as an indicator of source coronal electron temperature, while the core electron temperature has also been found to correlate with the solar wind velocity in the inner heliosphere. Here we investigate how well solar wind electron populations retain imprints of coronal electron temperature. Using Solar Orbiter measurements at ∼0.5 au, we fit three components (i.e., the core, halo, and strahl) of the electron velocity distribution function and compare the resulting strahl and core temperatures with heavy-ion charge-state ratios, which serve as proxies for the coronal electron temperature. We present the first clear evidence from inner heliosphere observations that, in several individual streams, a proxy for the strahl parallel temperature, Tstrahl,∥, correlates significantly and positively with the charge-state ratios O7+/O6+ and C6+/C5+. However, this correlation is not universally present, implying that many electron streams are significantly affected by transport processes, such as scattering, that erase the signature. We find that, notably, the core perpendicular temperature ( Tcore,⊥ ) also strongly correlates with the charge-state ratios. We interpret this result within the framework of the exospheric solar wind model. Our results suggest that both thermal and suprathermal electrons can at times retain coronal information, but that aggregating multiple streams can obscure the underlying relationships.

We develop and apply a bespoke fitting routine to a large volume of solar wind electron distribution data measured by Parker Solar Probe over its first five orbits, covering radial distances from 0.13 to 0.5 au. We characterize the radial evolution of the electron core, halo, and strahl populations in the slow solar wind during these orbits. The fractional densities of these three electron populations provide evidence for the growth of the combined suprathermal halo and strahl populations from 0.13 to 0.17 au. Moreover, the growth in the halo population is not matched by a decrease in the strahl population at these distances, as has been reported for previous observations at distances greater than 0.3 au. We also find that the halo is negligible at small heliocentric distances. The fractional strahl density remains relatively constant at ∼1% below 0.2 au, suggesting that the rise in the relative halo density is not solely due to the transfer of strahl electrons into the halo.