arXiv subjects

Hongyang Zhou

Publications and source records attributed to Hongyang Zhou.

18 recordsLinked to original sources

arXiv2026

Simultaneous Mars-orbit observations reveal Kelvin-Helmholtz instability-driven bulk atmospheric ion escape

Atmospheric ion escape driven by the solar wind is a key process controlling the long-term loss of the Martian atmosphere. Localized plasma clouds can carry substantial fluxes of planetary ions away from Mars, representing episodes of bulk escape. However, their origin has remained unclear due to the absence of simultaneous upstream measurements. Using joint observations from the MAVEN and Tianwen-1 missions, which provide real-time upstream monitoring, we present direct evidence that these plasma clouds are nonlinear wave packets generated by the Kelvin-Helmholtz instability (KHI). The spatial scale of KH waves is constrained for the first time via two-point measurements. Ion fluxes within plasma clouds are one to two orders of magnitude higher than those in typical steady-state escape channels. Our results indicate that KHI is an important process for solar wind coupling to planetary upper atmospheres and plays a crucial role in shaping atmospheric ion escape for unmagnetized planets.

physics.space-ph↗

arXiv2026

Direct Observations of Magnetic Reconnection in the Solar Wind Current Sheets near Mars

Magnetic reconnection is a fundamental and ubiquitous process in astrophysical plasmas that converts magnetic energy into plasma kinetic and thermal energy. Throughout the heliosphere, the solar wind is permeated with current sheets (CSs), providing a natural laboratory for investigating this process. Using measurements from NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we report the first direct observations of magnetic reconnection occurring within the solar wind CSs near Mars. Specifically, MAVEN observed the classic Petschek-type reconnection exhaust regions, evidenced by bifurcated magnetic field signatures and Alfvenic ion outflows. Notably, the observed exhaust region appears to be large-scale, significantly exceeding the typical thickness of solar wind CSs near Mars. This suggests that magnetic reconnection may significantly broaden the CS. Our results underscore the ubiquity of magnetic reconnection across heliocentric distances and may provide new insights into the large-scale evolution of the solar wind and the development of turbulence within it.

physics.space-ph↗

arXiv2026

Properties and Radial Evolution of Solar Wind Turbulence Near Mercury's Orbit

We present a comprehensive statistical study of the radial evolution of solar wind turbulence near Mercury's orbit using long-term magnetic field measurements from the MESSENGER mission. Owing to Mercury's highly elliptical orbit and the spacecraft's repeated, extended residence in the upstream solar wind, the data set provides more than 17,000 hours of observations, enabling robust statistics across well-defined heliocentric distance intervals (0.31-0.47 au). We find that inertial-range spectral slopes remain close to -3/2 throughout Mercury's orbit, showing no significant radial evolution. Combined with low magnetic compressibility, this result indicates a stable, predominantly Alfvenic inertial-range cascade already established here. In contrast, kinetic-range spectral slopes exhibit clear radial evolution, becoming progressively shallower with increasing heliocentric distance, highlighting the greater sensitivity of kinetic-scale turbulence to heliocentric conditions. The ion-scale spectral break frequency decreases with distance in the spacecraft frame, while its normalized form increases relative to the local proton cyclotron frequency, demonstrating that the break is not tied to proton cyclotron frequency but reflects evolving local plasma conditions. Magnetic compressibility shows a similar frequency dependence at all distances, with a subtle radial enhancement of compressive fluctuations at kinetic scales. Autocorrelation analysis reveals strong anisotropy, with the correlation times of field-aligned magnetic fluctuations increasing with heliocentric distance, while those of perpendicular fluctuations remain shorter and nearly invariant. Together, these results demonstrate a clear scale-dependent radial evolution of solar wind turbulence near Mercury-s orbit, providing new constraints on the development of kinetic processes in the inner heliosphere.

physics.space-ph↗

arXiv2026

Automated Classification of Plasma Regions at Mars Using Machine Learning

The plasma environment around Mars is highly variable because it is strongly influenced by the solar wind. Accurate identification of plasma regions around Mars is important for the community studying solar wind-Mars interactions, region-specific plasma processes, and atmospheric escape. In this study, we develop a machine-learning-based classifier to automatically identify three key plasma regions--solar wind, magnetosheath, and induced magnetosphere--using only ion omnidirectional energy spectra measured by the MAVEN Solar Wind Ion Analyzer (SWIA). Two neural network architectures are evaluated: a multilayer perceptron (MLP) and a convolutional neural network (CNN) that incorporates short temporal sequences. Our results show that the CNN can reliably distinguish the three plasma regions, whereas the MLP struggles to separate the solar wind and magnetosheath. Therefore, the CNN-based approach provides an efficient and accurate framework for large-scale plasma region identification at Mars and can be readily applied to future planetary missions.

physics.space-ph↗

arXiv2025

Spectral Properties and Energy Injection in Mercury's Magnetotail Current Sheet

Mercury's magnetotail hosts a thin and highly dynamic current sheet (CS), where magnetic reconnection and strong fluctuations frequently occur. Here, we statistically analyze magnetic field power spectra across 370 magnetotail CSs observed by MESSENGER. About 20% of the events are quasi-laminar, showing single power-law spectra, whereas 80% are turbulent, exhibiting a spectral break separating inertial and kinetic ranges. A dawn-dusk asymmetry is identified: inertial-range slopes are systematically shallower on the dawnside, whereas kinetic-range slopes are steeper, indicating more developed turbulence there, consistent with the higher occurrence of reconnection-related processes on the dawnside. Component analysis shows that the transverse components, orthogonal to the tail-aligned principal field (BX), display shallow slopes near -1 in the inertial range, suggesting energy injection at ion scales rather than a classical inertial range. These results demonstrate that Mercury's unique plasma environment fundamentally reshapes the initiation of turbulence and the redistribution of energy in the magnetotail.

physics.space-ph↗

arXiv2025

Revisiting Mars' Induced Magnetic Field and Clock Angle Departures under Real-Time Upstream Solar Wind Conditions

Mars lacks a global intrinsic dipole magnetic field, but its interaction with the solar wind generates a global induced magnetosphere. Until now, most studies have relied on single-spacecraft measurements, which could not simultaneously capture upstream solar wind conditions and the induced magnetic fields, thereby limiting our understanding of the system. Here, we statistically re-examine the properties of Mars' induced magnetic field by incorporating, for the first time, real-time upstream solar wind conditions from the coordinated MAVEN and Tianwen-1 observations. Our results are show that both solar wind dynamic pressure and the interplanetary magnetic field (IMF) magnitude enhance the strength of the induced magnetic field, but they exert opposite effects on the compression ratio: higher dynamic pressure strengthens compression, while stronger IMF weakens it. The induced field is stronger under quasi-perpendicular IMF conditions compared with quasi-parallel IMF, reflecting a stronger mass-loading effect. We further investigate the clock angle departures of the induced fields. They remain relatively small in the magnetosheath near the bow shock, increase gradually toward the induced magnetosphere, and become significantly larger within the induced magnetosphere. In addition, clock angle departures are strongly enhanced under quasi-parallel IMF conditions. Their dependence on upstream drivers further shows that, within the magnetosheath, clock angle departures are minimized under low dynamic pressure, high IMF magnitude, and low Alfven Mach number conditions. These results may enhance our understanding of solar wind interaction with Mars, and highlight the critical role of multi-point observations.

physics.space-ph↗

arXiv2025

Physics-Informed Neural Networks for Modeling the Martian Induced Magnetosphere

Understanding the magnetic field environment around Mars and its response to upstream solar wind conditions provide key insights into the processes driving atmospheric ion escape. To date, global models of Martian induced magnetosphere have been exclusively physics-based, relying on computationally intensive simulations. For the first time, we develop a data-driven model of the Martian induced magnetospheric magnetic field using Physics-Informed Neural Network (PINN) combined with MAVEN observations and physical laws. Trained under varying solar wind conditions, including B_IMF, P_SW, and {\theta}_cone, the data-driven model accurately reconstructs the three-dimensional magnetic field configuration and its variability in response to upstream solar wind drivers. Based on the PINN results, we identify key dependencies of magnetic field configuration on solar wind parameters, including the hemispheric asymmetries of the draped field line strength in the Mars-Solar-Electric coordinates. These findings demonstrate the capability of PINNs to reconstruct complex magnetic field structures in the Martian induced magnetosphere, thereby offering a promising tool for advancing studies of solar wind-Mars interactions.

astro-ph.EP↗

arXiv2025

Body Management Information Practices on a Female-dominant Platform

With growing awareness of long-term health and wellness, everyday body management has become a widespread practice. Social media platforms and health-related applications offer abundant information for those pursuing healthier lifestyles and more positive body images. While prior Human-Computer Interaction research has focused extensively on technology-mediated health interventions, the user-initiated practices of browsing and evaluating body management information remain underexplored. In this paper, we study a female-dominant social media platform in China to examine how users seek such information and how it shapes their lifestyle choices. Through semi-structured interviews with 18 users, we identify factors including consumerism, poster popularity, and perceived authenticity that influence decision-making, alongside challenges such as discerning reliable methods and managing body anxiety triggered by social media. We contribute insights into how content and media formats interact to shape users' information evaluation, and we outline design implications for supporting more reliable and healthy engagements with body management information.

cs.HC↗

arXiv2025

Magnetic Field and Plasma Asymmetries Between the Martian Quasi-Perpendicular and Quasi-Parallel Magnetosheaths

The Martian magnetosheath acts as a conduit for mass and energy transfer between the upstream solar wind and its induced magnetosphere. However, our understanding of its global properties remains limited. Using nine years of data from NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we performed a quantitative statistical analysis to explore the spatial distribution of the magnetic fields, solar wind and planetary ions in the magnetosheath. We discovered significant asymmetries in the magnetic field, solar wind protons, and planetary ions between the quasi-perpendicular and quasi-parallel magnetosheaths. The asymmetries in the Martian magnetosheath exhibit both similarities and differences compared to those in the Earth's and Venus' magnetosheaths. These results indicate that the Martian magnetosheath is distinctly shaped by both shock geometry and planetary ions.

physics.space-ph↗

arXiv2025

Similarity Matters: A Novel Depth-guided Network for Image Restoration and A New Dataset

Image restoration has seen substantial progress in recent years. However, existing methods often neglect depth information, which hurts similarity matching, results in attention distractions in shallow depth-of-field (DoF) scenarios, and excessive enhancement of background content in deep DoF settings. To overcome these limitations, we propose a novel Depth-Guided Network (DGN) for image restoration, together with a novel large-scale high-resolution dataset. Specifically, the network consists of two interactive branches: a depth estimation branch that provides structural guidance, and an image restoration branch that performs the core restoration task. In addition, the image restoration branch exploits intra-object similarity through progressive window-based self-attention and captures inter-object similarity via sparse non-local attention. Through joint training, depth features contribute to improved restoration quality, while the enhanced visual features from the restoration branch in turn help refine depth estimation. Notably, we also introduce a new dataset for training and evaluation, consisting of 9,205 high-resolution images from 403 plant species, with diverse depth and texture variations. Extensive experiments show that our method achieves state-of-the-art performance on several standard benchmarks and generalizes well to unseen plant images, demonstrating its effectiveness and robustness.

cs.CV↗

arXiv2025

Unsupervised Real-World Super-Resolution via Rectified Flow Degradation Modelling

Unsupervised real-world super-resolution (SR) faces critical challenges due to the complex, unknown degradation distributions in practical scenarios. Existing methods struggle to generalize from synthetic low-resolution (LR) and high-resolution (HR) image pairs to real-world data due to a significant domain gap. In this paper, we propose an unsupervised real-world SR method based on rectified flow to effectively capture and model real-world degradation, synthesizing LR-HR training pairs with realistic degradation. Specifically, given unpaired LR and HR images, we propose a novel Rectified Flow Degradation Module (RFDM) that introduces degradation-transformed LR (DT-LR) images as intermediaries. By modeling the degradation trajectory in a continuous and invertible manner, RFDM better captures real-world degradation and enhances the realism of generated LR images. Additionally, we propose a Fourier Prior Guided Degradation Module (FGDM) that leverages structural information embedded in Fourier phase components to ensure more precise modeling of real-world degradation. Finally, the LR images are processed by both FGDM and RFDM, producing final synthetic LR images with real-world degradation. The synthetic LR images are paired with the given HR images to train the off-the-shelf SR networks. Extensive experiments on real-world datasets demonstrate that our method significantly enhances the performance of existing SR approaches in real-world scenarios.

cs.CV↗

arXiv2025

Observation of a Knotted Electron Diffusion Region in Earth's Magnetotail Reconnection

Magnetic reconnection is a fundamental plasma process that alters the magnetic field topology and releases magnetic energy. Most numerical simulations and spacecraft observations assume a two-dimensional diffusion region, with the electron diffusion region (EDR) embedded in the same plane as the ion diffusion region (IDR) and a uniform guide field throughout. Using observations from Magnetospheric Multiscale (MMS) mission, we report a non-coplanar, knotted EDR in Earth's magnetotail current sheet. The reconnection plane of the knotted EDR deviates by approximately 38{\deg} from that of the IDR, with the guide field exhibiting both a 38{\deg} directional shift and a twofold increase in amplitude. Moreover, the Hall magnetic field is bipolar in the EDR but quadrupolar in the IDR, indicating different Hall current structures at electron and ion scales. These observations highlight the importance of three-dimensional effects and illustrate the complexity of multiscale coupling between the EDR and IDR during reconnection studies.1

physics.space-ph↗

arXiv2025

Suppressing spurious oscillations and particle noise in particle-in-cell simulations

Particle-in-cell (PIC) simulations are essential for studying kinetic plasma processes, but they often suffer from statistical noise, especially in plasmas with fast flows. We have also found that the typical central difference scheme used in PIC codes to solve Maxwell's equations produces spurious oscillations near discontinuities, which can lead to unphysical solutions. In this work, we present numerical techniques to address these challenges within the semi-implicit PIC code FLEKS, which is based on the Gauss's Law-satisfying Energy-Conserving Semi-Implicit Particle-in-Cell method (GL-ECSIM). First, we introduce a Lax-Friedrichs-type diffusion term with a flux limiter into the Maxwell solver to suppress unphysical oscillations near discontinuities. Second, we propose a novel approach for calculating the current density in the comoving frame, which significantly reduces particle noise in simulations with fast plasma flows. Numerical tests are presented to demonstrate the effectiveness of these methods in mitigating spurious oscillations and noise in shock and magnetic reconnection simulations.

physics.comp-ph↗

arXiv2025

Planar Collisionless Shock Simulations with Semi-Implicit Particle-in-Cell Model FLEKS

This study investigates the applicability of the semi-implicit particle-in-cell code FLEKS to heliospheric shock simulations. We examine one- and two-dimensional local planar shock simulations, initialized using MHD states with upstream conditions representative of plasmas in the hypersonic, $\beta\sim 1$ regime, for both quasi-perpendicular and quasi-parallel configurations. The refined algorithm in FLEKS proves robust, enabling accurate shock simulations with a grid resolution on the order of the electron inertial length $d_e$. Our simulations successfully capture key shock features, including shock structures (foot, ramp, overshoot, and undershoot), upstream and downstream waves (fast magnetosonic, whistler, Alfv\'en ion-cyclotron, and mirror modes), and non-Maxwellian particle distributions. Crucially, we find that at least two spatial dimensions are critical for accurately reproducing downstream wave physics in quasi-perpendicular shocks and capturing the complex dynamics of quasi-parallel shocks, including surface rippling, shocklets, SLAMS, magnetic reconnection and jets. Furthermore, our parameter studies demonstrate the impact of mass ratio and grid resolution on shock physics. This work provides valuable guidance for selecting appropriate physical and numerical parameters for shock simulations using a semi-implicit PIC method, paving the way for incorporating kinetic shock processes into large-scale collisionless plasma simulations with the MHD-AEPIC model.

physics.space-ph↗

arXiv2025

BATSRUS GPU: Faster-than-Real-Time Magnetospheric Simulations with a Block-Adaptive Grid Code

BATSRUS, our state-of-the-art extended magnetohydrodynamic code, is the most used and one of the most resource-consuming models in the Space Weather Modeling Framework. It has always been our objective to improve its efficiency and speed with emerging techniques, such as GPU acceleration. To utilize the GPU nodes on modern supercomputers, we port BATSRUS to GPUs with the OpenACC API. Porting the code to a single GPU requires rewriting and optimizing the most used functionalities of the original code into a new solver, which accounts for around 1% of the entire program in length. To port it to multiple GPUs, we implement a new message passing algorithm to support its unique block-adaptive grid feature. We conduct weak scaling tests on as many as 256 GPUs and find good performance. The program has 50-60% parallel efficiency on up to 256 GPUs, and up to 95% efficiency within a single node (4 GPUs). Running large problems on more than one node has reduced efficiency due to hardware bottlenecks. We also demonstrate our ability to run representative magnetospheric simulations on GPUs. The performance for a single A100 GPU is about the same as 270 AMD "Rome" CPU cores, and it runs 3.6 times faster than real time. The simulation can run 6.9 times faster than real time on four A100 GPUs.

astro-ph.IM↗

arXiv2024

Inverse-like Antagonistic Scene Text Spotting via Reading-Order Estimation and Dynamic Sampling

Scene text spotting is a challenging task, especially for inverse-like scene text, which has complex layouts, e.g., mirrored, symmetrical, or retro-flexed. In this paper, we propose a unified end-to-end trainable inverse-like antagonistic text spotting framework dubbed IATS, which can effectively spot inverse-like scene texts without sacrificing general ones. Specifically, we propose an innovative reading-order estimation module (REM) that extracts reading-order information from the initial text boundary generated by an initial boundary module (IBM). To optimize and train REM, we propose a joint reading-order estimation loss consisting of a classification loss, an orthogonality loss, and a distribution loss. With the help of IBM, we can divide the initial text boundary into two symmetric control points and iteratively refine the new text boundary using a lightweight boundary refinement module (BRM) for adapting to various shapes and scales. To alleviate the incompatibility between text detection and recognition, we propose a dynamic sampling module (DSM) with a thin-plate spline that can dynamically sample appropriate features for recognition in the detected text region. Without extra supervision, the DSM can proactively learn to sample appropriate features for text recognition through the gradient returned by the recognition module. Extensive experiments on both challenging scene text and inverse-like scene text datasets demonstrate that our method achieves superior performance both on irregular and inverse-like text spotting.

cs.CV↗

arXiv2023

Hate Raids on Twitch: Understanding Real-Time Human-Bot Coordinated Attacks in Live Streaming Communities

Online harassment and content moderation have been well-documented in online communities. However, new contexts and systems always bring new ways of harassment and need new moderation mechanisms. This study focuses on hate raids, a form of group attack in real-time in live streaming communities. Through a qualitative analysis of hate raids discussion in the Twitch subreddit (r/Twitch), we found that (1) hate raids as a human-bot coordinated group attack leverages the live stream system to attack marginalized streamers and other potential groups with(out) breaking the rules, (2) marginalized streamers suffer compound harms with insufficient support from the platform, (3) moderation strategies are overwhelmingly technical, but streamers still struggle to balance moderation and participation considering their marginalization status and needs. We use affordances as a lens to explain how hate raids happens in live streaming systems and propose moderation-by-design as a lens when developing new features or systems to mitigate the potential abuse of such designs.

cs.HC↗

arXiv2023

First 3D hybrid-Vlasov global simulation of auroral proton precipitation and comparison with satellite observations

The precipitation of charged particles from the magnetosphere into the ionosphere is one of the crucial coupling mechanisms between these two regions of geospace and is associated with multiple space weather effects, such as global navigation satellite system signal disruption and geomagnetically induced currents at ground level. While precipitating particle fluxes have been measured by numerous spacecraft missions over the past decades, it often remains difficult to obtain global precipitation patterns with a good time resolution during a substorm. Numerical simulations can help to bridge this gap and improve the understanding of mechanisms leading to particle precipitation at high latitudes through the global view they offer on the near-Earth space system. We present the first results on auroral (0.5-50 keV) proton precipitation within a 3-dimensional simulation of the Vlasiator hybrid-Vlasov model. The run is driven by southward interplanetary magnetic field conditions with constant solar wind parameters. We find that, on the dayside, cusp proton precipitation exhibits the expected energy-latitude dispersion and takes place in the form of successive bursts associated with the transit of flux transfer events formed through dayside magnetopause reconnection. On the nightside, the precipitation takes place within the expected range of geomagnetic latitudes, and it appears clearly that the precipitating particle injection is taking place within a narrow magnetic local time span, associated with fast Earthward plasma flows in the near-Earth magnetotail. Finally, the simulated precipitating fluxes are compared to observations from Defense Meteorological Satellite Program spacecraft during driving conditions similar to those in the simulation and are found to be in good agreement with the measurements.

physics.space-ph↗