We have studied the ionospheric response at near-equator latitudes during the geomagnetic storm of 26 August 2018, which was the strongest geomagnetic disturbance that year (minimum Dst value: −174 nT). For the analysis, we considered the F2-layer critical frequency (foF2) and peak height (hmF2), as well as total electron content (TEC) data for Jicamarca (geographic coordinates: 12° S, 283.2° E; geomagnetic coordinates: 2.26° S, 4.09° W), Saoluis (geographic coordinates: 2.6° S, 315.8° E; geomagnetic coordinates: 5.94° N, 28.5° E), Guam (geographic coordinates: 13.4° N, 144.8° E; geomagnetic coordinates: 5.73° N, 143.2° W) and Libreville (geographic coordinates: 0.39° N, 9.45° E; geomagnetic coordinates: 1.64° N, 82.6° W). First, we observed pre-storm improvements, which could be due to previous moderate geomagnetic activity. Second, only one station (Jicamarca) clearly revealed a prompt penetration electric field (PPEF) effect when Bz turned strongly negative during the initial phase of the storm. Over the stations Saoluis and Guam, a PPEF effect was not evident. These stations presented pre-storm enhancements in foF2. In this case study, disturbed dynamo electric fields appear not to have played a crucial role in increasing electron density near equatorial regions during the recovery phase because the observed disturbances did not correspond with those produced by these electric fields, that is, negative (positive) storm effects on the dayside (night). Third, the increases in electron density observed during recovery are most likely caused by neutral composition changes.

中文翻译：

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2018 年 8 月 26 日赤道/低纬度地磁风暴电离层响应的纵向变化

我们研究了 2018 年 8 月 26 日地磁风暴期间近赤道纬度的电离层响应，这是当年最强的地磁扰动（最小 Dst 值：-174 nT）。在分析中，我们考虑了 Jicamarca 的 F2 层临界频率 (foF2) 和峰高 (hmF2) 以及总电子含量 (TEC) 数据（地理坐标：12° S，283.2° E；地磁坐标：2.26 ° S，4.09° W），Saoluis（地理坐标：2.6° S，315.8° E；地磁坐标：5.94° N，28.5° E），关岛（地理坐标：13.4° N，144.8° E；地磁坐标：5.73 ° N，143.2° W）和利伯维尔（地理坐标：0.39° N，9.45° E；地磁坐标：1.64° N，82.6° W）。首先，我们观察到风暴前的改善，这可能是由于之前的中等地磁活动造成的。第二，只有一个台站 (Jicamarca) 清楚地揭示了在风暴初始阶段 Bz 变为强烈负值时的瞬发电场 (PPEF) 效应。在 Saoluis 和关岛站，PPEF 效应不明显。这些台站在 foF2 中展示了风暴前的增强功能。在这个案例研究中，在恢复阶段，受干扰的发电机电场似乎没有在增加赤道地区附近的电子密度方面发挥关键作用，因为观察到的干扰与这些电场产生的干扰不对应，即负（正）白天（夜间）的风暴影响。第三，在恢复过程中观察到的电子密度增加很可能是由中性成分变化引起的。