The study of space-weather effects and more specifically Forbush decreases of the cosmic-ray intensity depends on space and ground measurements. Very often Forbush decreases and geomagnetic storms are accompanied by pre-increases and/or pre-decreases manifested in cosmic-ray behavior, known as precursory signs. These cosmic-ray intensity variations do not coincide with the shock arrival but begin well before (up to 24 hours) the onset of the main event. In this study a group of large Forbush decreases with amplitude ≥ 4% was examined for precursors. According to the helio-longitude of the solar source, the events were separated into three categories: western (\(21^{\circ} \leq \) helio-longitude ≤ 60^∘), eastern (\(-60^{\circ} \leq \) helio-longitude \(\leq -21^{\circ}\)), and central (\(-20^{\circ} \leq \) helio-longitude \(\leq 20^{\circ}\)). The selected events cover 1967 – 2017. The analysis of the Forbush decreases and the plotting of the asymptotic longitudinal cosmic-ray distribution diagrams were based on the “Global Survey Method” and the “Ring of Stations” method, respectively. Data on solar flares, solar-wind speed, interplanetary magnetic field, and geomagnetic indices (Kp and Dst) were also used. The results show the clear signs of precursors in a significant number of events.

对空间天气效应的研究，更具体地说，宇宙射线强度的 Forbush 衰减取决于空间和地面测量。Forbush 减少和地磁风暴经常伴随着宇宙射线行为中的预增加和/或预减少，称为前兆。这些宇宙射线强度变化与冲击波的到来并不一致，而是在主要事件发生之前（最多 24 小时）就开始了。在这项研究中，检查了一组幅度≥ 4% 的大型 Forbush 下降的前体。根据太阳源的日经度，将事件分为三类：西部（\(21^{\circ} \leq \) helio-longitude ≤ 60 ^∘），东部（\(-60^{\ circ} \leq \)日经度\(\leq -21^{\circ}\)）和中央（\(-20^{\circ} \leq \)日经度\(\leq 20^{\circ}\)）。所选事件涵盖1967-2017年。Forbush递减分析和渐近纵向宇宙射线分布图的绘制分别基于“全球巡天法”和“环站”法。还使用了有关太阳耀斑、太阳风速、行星际磁场和地磁指数（Kp 和 Dst）的数据。结果显示了大量事件中前兆的明显迹象。