The Moon-Aiming Thai-Chinese Hodoscope (MATCH) is a particle detector developed for the Chang'E-7 mission, designed to support space weather monitoring and cosmic radiation studies within the Sun-Earth-Moon system. The primary observational objectives of MATCH include space weather science and alerts, as well as the detection of cosmic radiation, particularly Jovian and Galactic Cosmic Ray (GCR) electrons. Additionally, MATCH can detect lunar albedo ions (alpha particles and protons) and contribute to understanding cosmic-ray interactions with the lunar surface, including high-energy particle backscattering mechanisms. These studies are essential for improving our knowledge of cosmic ray propagation and energy distribution in the lunar environment. MATCH integrates a double-sided silicon strip detector (DSSD) for precise position tracking of incoming particles, along with a bismuth germanate (BGO) scintillator stack for accurate energy measurements. This study presents the development and validation of a scalable ground software architecture that supports event detection, signal processing, and data calibration, optimized for constrained onboard resources. The system has been validated through hardware-in-the-loop (HIL) testing using alpha-emitting sources under mission-equivalent conditions, demonstrating high accuracy and resource efficiency for on-orbit data acquisition modes. Once deployed, MATCH is expected to provide the first continuous MeV-range cosmic electron measurements from lunar orbit, enabling new insights into Jovian and Galactic cosmic ray propagation, space weather variability, and lunar albedo ion generation. The software architecture developed here plays a critical role in enabling astrophysical investigations during the upcoming Chang'E-7 mission. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Using particle-in-cell simulations that label ions and electrons according to their initial inflow region, we find that during 2D collisionless magnetic reconnection, the bulk flow of the plasma from each inflow side crosses paths with plasma from the other inflow side and crosses the midplane before being redirected into an outflow jet. This feature, which we term "flow crossover," implies mechanisms to generate bulk motion in a direction parallel to the magnetic field. We find that ions and electrons undergo different parallel driving mechanisms, leading to different flow crossover patterns. The parallel bulk flow for ions is generated more locally within the ion diffusion region, whereas the parallel bulk flow for electrons is mostly generated outside the electron diffusion region. Consequently, the reconnection outflows are more of a parallel flow than a perpendicular flow, especially for the electron outflow. The flow crossover and the parallel outflow patterns occur not only in symmetric reconnection but also in the more complex scenario of a guide-field asymmetric reconnection, suggesting that it is a general feature of collisionless magnetic reconnection. Because the plasma outflow on one side of the midplane mostly originates from the inflow plasma on the other side, we predict that near an asymmetric reconnection site in a collisionless space plasma, in situ observations across the outflow region could reveal locally reversed gradients in plasma properties. These results are potentially important for quantifying transport across the dayside magnetopause of Earth and other planets and the energy partition in reconnection, including electron and ion heating.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

Averaging techniques in solar wind measurements have been a longstanding subject of debate. Using Parker Solar Probe (PSP) observations from encounters 1 to 19, we investigate how averaging timescales influence the characterization of turbulent properties across the Alfvenic transition. We compute the rolling mean Alfven Mach number over various averaging intervals, which are then analyzed against switchbacks, magnetic fluctuation energy, and correlation time. We find that the distribution of subAlfvenic intervals is relatively insensitive to judiciously-chosen averaging scales. In contrast, magnetic fluctuation energies increase systematically with larger averaging window, while maintaining a consistent profile across the Alfven transition. We further show that the effective magnetic correlation time decreases with decreasing heliocentric distance and MA, reaching values of several minutes approaching MA =1. These results demonstrate the importance of choosing physically meaningful backgrounds for turbulence parameters, such as the correlation scales, and their impacts on characterizing the solar wind.

Magnetic switchbacks are large amplitude deflections of the magnetic field within the solar wind. They are Alfvénic in character and so are associated with a spike in velocity and a generally small variation in local plasma density. Early orbits of Parker Solar Probe revealed that the solar wind near the Sun is dominated by these structures, and therefore, they may be playing an important role in the energy budget and acceleration of the young solar wind. In this review, we present an overview of different mechanisms that have been proposed for how switchbacks could be formed. We group the mechanisms by whether they predominantly act in the low solar atmosphere or within the solar wind (in situ). We focus on mechanisms that can create reversals of the ambient magnetic field direction and, thus, account for the most extreme perturbations. The general consensus is that mechanisms in the lower solar atmosphere do not form such reversals on their own but provide the seed perturbations, flows, or particle beams necessary for in situ mechanisms to create switchbacks within the solar wind. Switchback observations thus likely contain an imprint of the coronal source of the seed perturbation or flow, which is evolved further locally by one of several plausible in situ mechanisms. We discuss the strengths and weaknesses of each mechanism and outline future observational and theoretical tests that could help differentiate between them.

Neutron monitors (NMs) are ground-based devices designed to measure cosmic-ray count rates by monitoring atmospheric neutrons from cosmic-ray showers. We present results from new electronics that have recorded cross-counter time delay histograms for the Princess Sirindhorn Neutron Monitor (PSNM) at the summit of Doi Inthanon, Thailand. From these histograms, we have extracted the cross-counter leader fraction (L) and corrected it for atmospheric effects. For large counter separation, we measure nearly constant L≈0.997, implying that 0.3% of counts in one counter are temporally associated with later counts on a given distant counter. Monte Carlo simulations confirm that individual secondary particles cannot account for the associated counts at large counter separation, which instead requires a contribution from multiple secondary particles in the same cosmic ray shower that is apparently independent of distance over 3 to 7.5 m. We infer that ≈4.5% of PSNM counts are associated with a later count in at least one of its 18 counters from a different secondary particle in the same shower. Monte Carlo simulations of atmospheric showers and NM yield functions can be validated using our measurements of neutron multiplicity across counters and the contributions of single and multiple secondary particles. These measurements also improve understanding of the single-counter L, which has been used for precise tracking of cosmic-ray spectral variations and extending the range of NM observations to higher energies.

Close to the Sun, Parker Solar Probe (PSP) traverses the sub-Alfv & eacute;nic solar wind, a magnetically controlled plasma environment. Farther from the Sun, the magnetic field amplitude and plasma density weaken enough to establish a super-Alfv & eacute;nic environment where kinetic energy and turbulence become more prominent. Switchbacks (i.e. large directional deviations from the mean field) are shown to occur almost exclusively in the super-Alfv & eacute;nic regime. In this study, we analyse magnetic fluctuations from PSP encounters 8 through 19 to study their relationship to Alfv & eacute;n Mach number ($M_\mathrm{ A}$) and switchback parameter (Z). We find that the fluctuation of the magnetic field magnitude normalized to the mean magnetic field and of the radial velocity normalized to local Alfv & eacute;n speed increase with both Alfv & eacute;n Mach number and switchback parameter. However, there is distinct saturation in the increments of the normalized radial velocity fluctuations in the Alfv & eacute;n Mach number range of $\sim$4-6. Results are interpreted in terms of the Chandrasekhar criterion for Kelvin-Helmholtz activity. Overall, these findings are in agreement with earlier studies suggesting switchback generation through non-linear shear flow dynamics.

Abstract Large Forbush decreases (FDs) in the Galactic cosmic ray flux were observed by the paired neutron monitor (SNM) and the vertical channel of the muon detector (SMDV) at the Antarctic Syowa Station in May and October, 2024. The maximum count rate depressions in SNM and SMDV are $$\sim$$ ∼ 10% and $$\sim$$ ∼ 5% in the May FD, respectively. In the October FD, the observed count rates decreased in two steps following two successive interplanetary shocks. The maximum count rate depression recorded by SNM (SMDV) is $$\sim$$ ∼ 7% ( $$\sim$$ ∼ 3%) in the first step, while it is $$\sim$$ ∼ 8% ( $$\sim$$ ∼ 5%) in the second step. It is demonstrated that the SNM count rate fraction relative to the total count rate in SNM and SMDV ( $$F_n$$ F n ) is a good real-time indicator of the temporal variation of the cosmic ray rigidity spectrum ( $$\Delta \Gamma (P,t)$$ Δ Γ ( P , t ) ), which is an important parameter for identifying the physical processes responsible for FD effects. It is verified that the variation of $$F_n$$ F n is consistent with $$\Delta \Gamma (P,t)$$ Δ Γ ( P , t ) calculated from the Global Fitting Analysis (GFA) at the Syowa Station. $$F_n$$ F n also shows a significant increase of $$\Delta \Gamma (P,t)$$ Δ Γ ( P , t ) during the ground-level enhancement (GLE) due to solar energetic particles on May 11 superposed on the FD recovery phase, implying that the total (Galactic + solar) cosmic ray spectrum is softened due to the contribution from GLE intensity steeply increasing with decreasing rigidity. This implies that $$F_n$$ F n can be also a good indicator of small GLEs which are sometimes difficult to identify in the count rate variation when masked by an FD and the associated diurnal anisotropy. Graphic Abstract

Close to Earth, the solar wind is usually super-Alfvénic, i.e., the speed of the solar wind is much larger than the Alfvén speed. However, in the lower coronal regions, the solar wind is mostly sub-Alfvénic. With the Parker Solar Probe (PSP) crossing the boundary between the sub- and super-Alfvénic flow, R. Bandyopadhyay et al. performed a turbulence characterization of the sub-Alfvénic solar wind with initial data from encounters 8 and 9. In this study, we reexamine the turbulence properties such as turbulence amplitude, anisotropy of the magnetic field variance, intermittency, and switchback strength using PSP data from encounters 8–19. The later orbits probe lower altitudes and experience sub-Alfvénic conditions more frequently, providing a greater statistical coverage to contrast sub- and super-Alfvénic solar wind. These later orbits also extend the observations from near solar minimum at launch to near solar maximum conditions. Also, by isolating the intervals where the solar wind speed is approximately equal to the Alfvén speed, we explore the transition in more detail. We show that the amplitude of the normalized magnetic field fluctuation is smaller for the sub-Alfvénic samples. While solar wind turbulence in general is shown to be anisotropic, the sub-Alfvénic samples are more anisotropic than the super-Alfvénic samples, in general. Further, we show that the sub- and super-Alfvénic samples do not show much distinction in terms of intermittency strength. Finally, consistent with prior results, we find no evidence for polarity reversing >90° switchbacks in the sub-Alfvénic solar wind.

This letter presents a signal calibration and energy resolution analysis of a double-sided silicon strip detector (DSSD) developed for charged particle detection in a lunar-based space environment. The detector is part of the Moon-Aiming Thai-Chinese Hodoscope, i.e., a proposed scientific payload for the Chang'E-7 lunar orbiter, aimed at monitoring space weather and lunar-surface particle interactions. To evaluate the DSSD's performance under vacuum conditions, alpha sources (Am-241 and Pu-239) were used to generate energy spectra, which were processed through baseline correction and histogram generation. Four peak models, i.e., Gaussian, Gaussian + Exponential Tail, exponentially modified Gaussian (EMG), and Hyper-EMG, were compared using nonlinear least squares. Results show that the Hyper-EMG model yields superior fits, especially for Am-241, achieving an average reduced chi-squared of 1.64 +/- 4.44 and energy resolution of 3.09% +/- 0.45%, with 22 out of 32 Akaike Information Criterion (AIC) wins. In contrast, Gaussian fits showed higher fitting errors (e.g., chi(2)/DoF up to 10.5) and the poorest resolution. AIC selection further confirms Hyper-EMG's robustness, while Gaussian fits were consistently inadequate. These findings support the use of tail-aware models, such as Hyper-EMG, for accurate energy reconstruction in spaceborne silicon detectors.

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. In this Letter, we report the measurements of the diffuse emission from the Galactic plane-covering Galactic longitudes from 15° to 235° and latitudes from -5° to +5°, in an energy range of 1 to 25 TeV-made with the Water Cherenkov Detector Array (WCDA) of the Large High Altitude Air Shower Observatory. After the sky regions of known sources are masked, the diffuse emission is detected with 24.6σ and 9.1σ significance in the inner Galactic plane (15°<l<125°, |b|<5°) and outer Galactic plane (125°<l<235°, |b|<5°), respectively. The WCDA spectra in both regions can be well described by a power-law function, with spectral indices of -2.67±0.05_{stat} in the inner region and -2.83±0.19_{stat} in the outer region, respectively. Combined with the Square Kilometer Array (KM2A) measurements at higher energies, a clear softening of the spectrum is found in the inner region, with change of spectral indices by ∼0.5 at a break energy around 30 TeV. The fluxes of the diffuse emission are higher by a factor of 1.5-2.7 than the model prediction assuming local cosmic ray spectra and the gas column density, which are consistent with those measured by the KM2A. Along the Galactic longitude, the spatial distribution of the diffuse emission shows deviation from that of the gas column density. The spectral shape of the diffuse emission may vary in different longitude regions. The WCDA measurements bridge the gap between the low-energy measurements by space detectors and the ultra-high-energy observations by KM2A and other experiments. These results suggest that improved modeling of the wideband diffuse emission is required.

During their propagation in the heliosphere, interplanetary coronal mass ejections (ICMEs) interact with galactic cosmic ray (GCR) particles, modifying their spectrum and driving anisotropies. We analyze the first large Forbush decrease (FD) of Solar Cycle 25 on 2021 November 3–5 by using multipoint in situ observations and neutron monitors to study the association between FD characteristics and ICME. We use the Grad–Shafranov reconstruction to infer the magnetic field configuration of the ICME. We model the neutron monitor response through primary spectrum and anisotropy. The primary spectrum is parameterized with the force-field approximation and the anisotropy is modeled through a spherical harmonic expansion. We optimize the model parameters during the FD by using ground-based observations provided by the worldwide neutron-monitor network. The model’s results are compared with space-based measurements of the differential proton flux measured by the HEPD-01 detector on board the CSES-01 satellite and of the integral counts of both the High-Energy Particle Detector (HEPD-01) and the High Energy Telescope on board the Solar Orbiter. Anisotropy develops during the ICME passage, within the magnetic flux rope (MFR) and is found to be bidirectional. The force-field parameterization of the primary GCR fluxes based on ground-based measurements is found to be in very good agreement with spacecraft observations in the sub-GeV range. The GCR anisotropy obtained by fitting the model to ground-based observations is consistent with interplanetary magnetic field observations. The results suggest that the local magnetic field has a substantial axial component that is aligned to the MFR axis, and determines the GCR anisotropy at the typical neutron monitor energies.

Identifying Galactic PeVatrons (PeV particle accelerators) from ultrahigh-energy (UHE, >100 TeV)gamma-ray sources plays a crucial role in revealing the origin of Galactic cosmic rays. The UHE source 1LHAASO J1857+0203u is suggested to be associated with HESS J1858+020, which may be attributed to the possible PeVatron candidate supernova remnant (SNR) G35.6-0.4 or H II region G35.6-0.5. We perform detailed analysis on the very-high-energy and UHE gamma-ray emissions toward this region with data from the Large High Altitude Air Shower Observatory (LHAASO). 1LHAASO J1857+0203u is detected with a significance of 11.6 sigma above 100 TeV, indicating the presence of a PeVatron. It has an extent of similar to 0 degrees.18 with a power-law (PL) spectral index of similar to 2.5 at 1-25 TeV and pointlike emission with a PL spectral index of similar to 3.2 above 25 TeV. Using archival CO and H I data, we identify some molecular and atomic clouds that may be associated with the TeV gamma-ray emissions. Our modeling indicates that the TeV gamma-ray emissions are unlikely to arise from clouds illuminated by the protons that escaped from SNR G35.6-0.4. In the scenario in which H II region G35.6-0.5 could accelerate particles to the UHE band, the observed GeV-TeV gamma-ray emission could be well explained by a hadronic model with a PL spectral index of similar to 2.0 and cutoff energy of similar to 450 TeV. However, an origin in an evolved pulsar wind nebula cannot be ruled out.