The paper summarizes the properties of precipitation of magnetospheric electrons with energy above several hundred keV recorded by observing X‐ray bremsstrahlung in the polar stratosphere above the Murmansk region, Russia, in 1961–2019. Precipitation occurrence rate demonstrates a clear dependence on the solar activity with a maximum at the decay phase of the 11‐year solar cycle, similarly to the variability in occurrences of the high‐speed solar wind streams (HSSWS). The energetic electron precipitation (EEP) event series is often initiated by a moderate geomagnetic storm caused by a HSSWS and continues during geomagnetic storm recovery. EEP demonstrates the seasonal rate variation with the maxima in occurrence rate around the spring and the autumn solstices and correlates with fluences of relativistic electrons in the outer radiation belt. For 59 years, 589 events of precipitation were observed. Analysis of the long‐term time series revealed a growing trend in the rate of precipitation occurrence, especially in the 1990s to 2000s that is not properly explained yet.

中文翻译：

---

长期气球观测中观测到的高能磁层电子降水的时间特征

本文总结了1961-2019年通过观测俄罗斯摩尔曼斯克地区上方平流层中的X射线致recorded记录的能量超过几百keV的磁层电子的沉淀特性。降水发生率显示出对太阳活动的明显依赖，并且在11年太阳周期的衰变阶段最大，这与高速太阳风（HSSWS）发生的变化类似。高能电子降水（EEP）事件序列通常由HSSWS引起的中度地磁风暴引发，并在地磁风暴恢复期间持续发生。EEP证明了春季和秋季至冬至前后的季节性变化率随最大发生率变化，并且与外辐射带中相对论电子的通量相关。59年以来，共观测到589次降雨。对长期时间序列的分析显示，降水发生率呈上升趋势，尤其是在1990年代至2000年代，这一现象尚未得到适当的解释。