Abstract. We study here energetic-electron ( E>30 keV) precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data come from the Finnish riometer (relative ionospheric opacity meter) chain from stations extending from auroral (IVA, 65.2 ∘ N geomagnetic latitude; MLAT) to subauroral (JYV, 59.0 ∘ N MLAT) latitudes. We find that sheaths and ejecta lead frequently to enhanced CNA ( >0.5 dB) both at auroral and subauroral latitudes, although the CNA magnitudes stay relatively low (medians around 1 dB). Due to their longer duration, ejecta typically lead to more sustained enhanced CNA periods (on average 6–7 h), but the sheaths and ejecta were found to be equally effective in inducing enhanced CNA when relative-occurrence frequency and CNA magnitude were considered. Only at the lowest-MLAT station, JYV, ejecta were more effective in causing enhanced CNA. Some clear trends of magnetic local time (MLT) and differences between the ejecta and sheaths were found. The occurrence frequency and magnitude of CNA activity was lowest close to midnight, while it peaked for the sheaths in the morning and afternoon/evening sectors and for the ejecta in the morning and noon sectors. These differences may reflect differences in typical MLT distributions of wave modes that precipitate substorm-injected and trapped radiation belt electrons during the sheaths and ejecta. Our study also emphasizes the importance of substorms and magnetospheric ultra-low-frequency (ULF) waves for enhanced CNA.

中文翻译：

---

行星际日冕物质抛射鞘和抛射物期间粒子沉淀的宇宙噪声吸收特征

摘要。我们在这里使用宇宙噪声吸收 (CNA) 在 1997 年至 2012 年间在近地太阳风中观察到的 61 次行星际日冕物质抛射 (ICME) 的鞘和喷射物结构期间研究了高能电子 (E>30 keV) 沉淀。数据来自芬兰 riometer（相对电离层不透明度计）链，从极光（IVA，65.2 ∘ N 地磁纬度；MLAT）到亚极光（JYV，59.0 ∘ N MLAT）纬度的站点。我们发现鞘和喷射物经常导致极光和亚极光纬度的 CNA 增强（>0.5 dB），尽管 CNA 幅度保持相对较低（中位数约为 1 dB）。由于持续时间较长，喷射物通常会导致更持续的 CNA 增强期（平均 6-7 小时），但是当考虑相对发生频率和 CNA 幅度时，发现鞘和喷射物在诱导增强的 CNA 方面同样有效。只有在最低的 MLAT 站 JYV，喷射物才能更有效地引起 CNA 增强。发现了磁本地时间（MLT）的一些明显趋势以及喷射物和鞘之间的差异。CNA活动的发生频率和强度在接近午夜时最低，而在上午和下午/晚上扇区的鞘层以及上午和中午扇区的喷射物达到顶峰。这些差异可能反映了波模式的典型 MLT 分布的差异，这些波模式在鞘层和抛射物期间沉淀亚暴注入和捕获的辐射带电子。