Abstract Energetic charged particle precipitation associated with solar wind perturbations causes enhanced high-frequency radiowave absorption in the high-latitude ionosphere. This study models 38.2 MHz cosmic noise absorption (CNA) by utilising measurements from the Imaging Riometer for Ionospheric Studies (IRIS) at Kilpisjarvi, Finland obtained during solar cycle 23 (1996–2009) associated with the passage of interplanetary coronal mass ejections (ICMEs) past Earth; ICMEs are a major driver of enhanced geomagnetic activity. Superposed epoch analysis suggests that the r6absorption vs. time profile depends on whether ICME arrival occurs in the day-time (10–14 MLT) or night-time (22-02 MLT) for IRIS, with peak absorption occurring ~2–3 h ahead of ICME arrival or ~4 h after ICME arrival, respectively. We determine which combinations of solar wind and IMF parameters show the best correlation with the absorption associated with day-time or night-time arriving ICMEs using superposed epoch analysis and the least squares estimation method. Various combinations of solar wind parameters (including bulk velocity v, density n, and the interplanetary magnetic field north and south components Bz and the SYMH geomagnetic index), have been ranked to obtain the best coupling function for the absorption associated with day- and night-time arriving ICMEs. The absorption for day-time events is found to correlate closely with the solar wind dynamic pressure, SYMH, and the northward direction of the Bz while the absorption for night-time events is most closely related to the direction of the Bz and SYMH. The coupling functions are found to model the observed absorption successfully, with correlation coefficients of ~0.7–0.8 between the observed and modelled absorption.

中文翻译：

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行星际日冕物质抛射事件扰动期间极光吸收的经验建模

摘要 与太阳风扰动相关的高能带电粒子降水导致高纬度电离层的高频无线电波吸收增强。本研究利用芬兰基尔皮斯耶尔维的电离层研究成像测量仪 (IRIS) 的测量结果对 38.2 MHz 宇宙噪声吸收 (CNA) 进行建模，该测量值是在与行星际日冕物质抛射 (ICME) 相关的第 23 个太阳周期 (1996-2009) 期间获得的过去的地球；ICME 是地磁活动增强的主要驱动力。叠加历元分析表明 r6 吸收与时间曲线取决于 ICME 到达是在白天 (10-14 MLT) 还是夜间 (22-02 MLT) 到达 IRIS，峰值吸收发生约 2-3 小时分别在 ICME 到达前或 ICME 到达后约 4 小时。我们使用叠加历元分析和最小二乘估计方法确定太阳风和 IMF 参数的哪些组合显示出与白天或夜间到达 ICME 相关的吸收的最佳相关性。太阳风参数的各种组合（包括体积速度 v、密度 n 以及行星际磁场南北分量 Bz 和 SYMH 地磁指数）已被排序，以获得与昼夜相关的吸收的最佳耦合函数-时间到达ICME。发现白天事件的吸收与太阳风动态压力 SYMH 和 Bz 的向北方向密切相关，而夜间事件的吸收与 Bz 和 SYMH 的方向最密切相关。