Abstract The observations of vertical total electron content (VTEC) and L1 and L2 band ionospheric scintillations at an equatorial station, Tarawa (Geomag. Coordinates, 2.68°S, 114.26°W), Kiribati, under a complex severe space weather event of 4–9 September 2017, are presented. The VTEC increased significantly by 1.03 and 1.31 TEC units under M5.5 class flare at 20:28 UT on 04 September and M4.2 flare at 01:03 UT on 05 September, respectively, under the quiet geomagnetic conditions. A positive ionospheric storm with a maximum percentage change in VTEC (ΔVTEC%) of 16.7% followed by a negative ionospheric storm with ΔVTEC% of 32.8% occurred during the first main phase (Dst=- 142 nT) and recovery of 7–8 September storm. This positive ionospheric effect occurred due to the combined effects of prompt penetrating electric fields (PPEFs) and suddenly enhanced EUV and X-radiations associated with M class (3.9, 1.3 &1.2) flares whereas negative ionospheric effect could be accounted for the disturbance dynamo electric fields (DDEFs) and change in the storm-time O/N2 gas composition. A long duration (~10 h) positive ionospheric storm with a maximum ΔVTEC% of 26.3% was observed during the second main phase (Dst=-124 nT) which lasted well into its recovery. This is mainly due to the combined effect of PPEFs associated with the long duration of southward turning of Z - component of the interplanetary magnetic field of the second main phase and DDEFs of the first main phase. L1 and L2 band scintillations did not occur during both the phases of storm implying that ionospheric irregularities do not necessarily occur under severe geomagnetic storms. However, two events of nighttime scintillations one before and other after the storm were observed.

中文翻译：

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2017年9月4-9日空间天气事件下的赤道电离层TEC和闪烁：M级太阳耀斑和G4地磁风暴

摘要 赤道站塔拉瓦（地磁坐标，2.68°S，114.26°W），基里巴斯，在 4-4 度复杂的恶劣空间天气事件下，对垂直总电子含量 (VTEC) 和 L1 和 L2 波段电离层闪烁的观测。 2017 年 9 月 9 日，提交。在安静的地磁条件下，VTEC 分别在 9 月 4 日 20:28 UT 和 M4.2 耀斑下的 M5.5 级耀斑下显着增加了 1.03 和 1.31 TEC 单位，9 月 4 日 UT 20:03 UT。在第一个主要阶段 (Dst=- 142 nT) 和 9 月 7-8 日的恢复期间发生了一次正电离层风暴，其中 VTEC 的最大百分比变化 (ΔVTEC%) 为 16.7%，随后发生了一次负电离层风暴，ΔVTEC% 为 32.8%风暴。这种正电离层效应的发生是由于瞬时穿透电场 (PPEF) 以及与 M 级（3.9、1.3 和 1.2）耀斑相关的 EUV 和 X 辐射突然增强的综合效应，而负电离层效应可以解释扰动发电机电场 (DDEF) 和风暴时间 O/N2 气体成分的变化。在第二个主要阶段（Dst=-124 nT）观察到持续时间长（~10 小时）的正电离层风暴，最大 ΔVTEC% 为 26.3%，并持续到恢复阶段。这主要是由于与第二主相的行星际磁场 Z 分量和第一主相的 DDEF 长时间南转相关的 PPEF 的综合效应。L1 和 L2 波段闪烁在风暴的两个阶段都没有发生，这意味着在严重的地磁风暴下不一定会发生电离层的不规则性。然而，观测到了风暴前后的两次夜间闪烁事件。