AI 中文总结
研究近太阳磁折返的阿尔文icity、发生率和尺寸的径向演化，通过构建目录统计分析，发现其随径向距离、太阳活动等变化，且有各向异性，揭示了折返斑块形成及演化规律与太阳风条件的关系。
AI 中文摘要
以磁场方向反转特征的磁折返，被帕克太阳探测器（PSP）在日球层内部广泛观测到。随着PSP到达近日点附近10Rs，前24次交会的观测使得对r>10Rs处近太阳折返演化的研究成为可能。我们通过识别具有稳定场强和strahl电子极性的磁场反转，在10<r<55Rs范围内构建了一个折返目录。统计分析表明，折返阿尔文icity随径向距离增加而降低，与阿尔文临界点之外的太阳风演化一致。同时，折返发生率和空间尺寸随距离增加，表明在太阳风传播过程中持续产生和扩展。在给定径向距离处，包含折返的太阳风比例与背景太阳风径向速度（VR）和阿尔文马赫数（MA）正相关，而局部发生率主要由MA控制。这些结果表明，折返斑块优先在更快和更高MA的太阳风中形成。折返的空间尺寸对MA或VR没有明显依赖性，这意味着它们的尺寸演化可能不由源条件决定。太阳活动通过背景太阳风性质的变化影响折返演化，在太阳活动极小期，更高MA的折返比例更大。我们还进一步识别了相对于背景磁场方向的各向异性：垂直方向的局部发生率和空间尺寸大约是平行方向的1.5倍，表明折返斑块具有独特的磁拓扑结构。
英文摘要
Magnetic switchbacks, characterized by reversals of magnetic field direction, are widely observed in the inner heliosphere by Parker Solar Probe (PSP). With PSP reaching perihelia near 10Rs, observations from the first 24 encounters enable studies of near-Sun switchback evolution at r > 10Rs. We construct a switchback catalog within 10 < r < 55Rs by identifying magnetic field reversals with stable field magnitude and strahl-electron polarity. Statistical analysis shows that switchback Alfvenicity decreases with increasing radial distance, consistent with solar wind evolution beyond the Alfven critical point. Meanwhile, switchback occurrence rate and spatial size increase with distance, suggesting continued generation and expansion during solar wind propagation. At a given radial distance, the fraction of solar wind containing switchbacks is positively correlated with background solar wind radial velocity (VR) and Alfven Mach number (MA), while the local occurrence rate is mainly controlled by MA. These results suggest that switchback patches preferentially form in faster and higher-MA solar wind. The spatial size of switchbacks shows no clear dependence on MA or VR, implying that their size evolution is probably not determined by source conditions. Solar activity influences switchback evolution through changes in background solar wind properties, with a larger fraction of higher-MA switchbacks during solar minimum. We further identify anisotropy relative to the background magnetic field direction: the local occurrence rate and spatial size are approximately 1.5 times as large in the perpendicular direction as in the parallel direction, indicating distinct magnetic topology of switchback patches
Comments21 pages, 10 figures
