We present a statistical study of electromagnetic ion cyclotron (EMIC) waves observed at Antarctic station (geographic $$70.7{^\circ }\,\hbox {S}$$ 70.7 ∘ S , $$11.8{^\circ }\,\hbox {E}$$ 11.8 ∘ E , $$L=5$$ L = 5 ) on quiet and disturbed days during 2011–2017. The data span a fairly good period of both ascending and descending phases of the solar cycle 24, which has witnessed extremely low activity. We noted EMIC wave occurrence by examining wave power in different frequency ranges in the spectrogram. EMIC wave occurrence during ascending and descending phases of solar cycle 24, its local time, seasonal dependence and durations have been examined. There are total 2367 days for which data are available. Overall, EMIC waves are observed for 3166.5 h ( $$\approx 5.57\%$$ ≈ 5.57 % of total duration) which has contributions from 1263 days. We find a significantly higher EMIC wave occurrence during the descending phase ( $$\approx$$ ≈ 6.83%) as compared to the ascending phase ( $$\approx$$ ≈ 4.08%) of the solar cycle, which implies nearly a twofold increase in EMIC wave occurrence. This feature is attributed to the higher solar wind dynamic pressure during descending phase of solar activity. There is no evident difference in the percentage occurrence of EMIC waves on magnetically disturbed and quiet days. On ground, EMIC waves show marginally higher occurrence during winter as compared to summer. This seasonal tendency is attributed to lower electron densities and conductivities in the ionosphere, which can affect the propagation of EMIC waves through ionospheric ducts. In local time, the probability distribution function of EMIC wave occurrence shows enhancement during 11.7–20.7 LT (i.e., afternoon–dusk sector). Daily durations of EMIC waves are in the range of 5–1015 min and it is noted that the longer duration (240–1015 min) events are prevalent on quiet days and are mostly seen during the descending phase of solar cycle.

中文翻译：

---

太阳活动周期24期间南极亚极光站Maitri电磁离子回旋波的发生特征

我们展示了在南极站观测到的电磁离子回旋 (EMIC) 波的统计研究（地理 $70.7{^\circ }\,\hbox {S}$$ 70.7 ∘ S , $11.8{^\circ }\,\hbox {E}$$ 11.8 ∘ E , $$L=5$$ L = 5 ) 在 2011-2017 年安静和受干扰的日子。数据跨越了太阳活动周期 24 的上升和下降阶段的相当好的时期，其活动极低。我们通过检查频谱图中不同频率范围内的波功率来注意到 EMIC 波的发生。EMIC 波发生在太阳活动周期 24 的上升和下降阶段，其当地时间、季节依赖性和持续时间已被检查。共有 2367 天的可用数据。总体而言，EMIC 波被观测到 3166.5 小时（$$\approx 5.57\%$$ ≈ 总持续时间的 5.57%），其贡献来自 1263 天。我们发现与太阳周期的上升阶段（$$\approx$$ ≈ 4.08%）相比，在下降阶段（$$\approx$$ ≈ 6.83%）出现显着更高的 EMIC 波，这意味着近两倍EMIC 波发生的增加。这一特征归因于太阳活动下降阶段较高的太阳风动态压力。在磁扰和安静的日子里，EMIC 波的出现百分比没有明显差异。在地面上，与夏季相比，冬季的 EMIC 波发生率略高。这种季节性趋势归因于电离层中较低的电子密度和电导率，这会影响 EMIC 波通过电离层管道的传播。当地时间11.7-20日，EMIC波发生概率分布函数呈增强趋势。7 LT（即下午-黄昏扇区）。EMIC 波的每日持续时间在 5-1015 分钟的范围内，值得注意的是，持续时间较长（240-1015 分钟）的事件在安静的日子里普遍存在，并且主要出现在太阳活动周期的下降阶段。