Abstract We have investigated the spatio-temporal evolution of disturbed time post mid-night Equatorial Plasma Bubbles (EPBs) using Canadian Advanced Digital Ionosonde (CADI) located at dip equatorial station, Tirunelveli (8.73°N, 77.7°E, 0.23°N Dip. Lat.), all-sky imager (ASI) observations at low latitude station Panhala (16.48oN, 74.6oE, 11.1oN Dip. Lat.) and Gadanki Ionospheric Radar Interferometer (GIRI) at Gadanki (13.5°N, 79.2°E; 6.5°N Dip. Lat.) which is situated at few degrees towards east and south of Panhala on 02-03 February 2017 night. During this night, IMF Bz showed its periodic variation starting from 16:00 UT to 23:00 UT accompanied by decrease in SYM-H to as low as -35 nT indicating the onset of weak magnetic storm. The analyzed results suggested that cause of post-midnight EPBs could be due to manifestation of fluctuating eastward/westward electric field due to combined under-shielding/over-shielding Electric Fields and disturbance dynamo electric fields that led to rise and fall of the F-layer over dip equator. Interestingly, the EPBs over Panhala showed eastward motion initially that quickly reversed to westward later. Along with westward motion they also started growing until 21:30 UT. However, most of these EPBs disappeared with time except the one that started descending/shrinking towards southern side (i.e. towards equator). The rising and shrinking of EPBs is found to be fairly correlated with the equatorial vertical drifts. The westward drift of EPBs at Panhala and its anti-correlation with vertical drifts has been confirmed from CADI zonal/vertical drifts. Accordingly, the study also investigated the role of storm induced vertical Hall electric field as a possible cause for westward drifts and its anti-correlation with vertical drifts. However, GIRI observations do not show any significant westward drift on this night at Gadanki suggesting that there is a longitudinal gradient in the zonal drift of these EPBs. In addition to longitudinal drift reversal, the latitudinal gradient in zonal drifts also has been noticed. The present work highlights the role of storm induced disturbances in the generation and evolution of post-midnight EPBs which is believed to be triggered by weak magnetic disturbances in the deep low solar minimum.

中文翻译：

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对午夜后赤道等离子体气泡 (EPB) 的风暴时间演变及其在印度扇区上空漂移的无线电和光学研究

摘要 我们使用位于倾角赤道站 Tirunelveli (8.73°N, 77.7°E, 0.23°N Dip) 的加拿大高级数字离子探空仪 (CADI) 研究了午夜赤道等离子体气泡 (EPB) 后扰动时间的时空演化。 . Lat.)，全天成像仪 (ASI) 在低纬度站 Panhala（16.48oN，74.6oE，11.1oN 倾角纬度）和 Gadanki（13.5°N，79.2°E）的 Gadanki 电离层雷达干涉仪 (GIRI) 观测; 6.5°N Dip. Lat.) 于 2017 年 2 月 2 日至 3 日晚上位于 Panhala 以东和以南几度。在这个晚上，IMF Bz 显示出从 16:00 UT 到 23:00 UT 的周期性变化，伴随着 SYM-H 下降到低至 -35 nT，表明弱磁暴开始。分析结果表明，导致午夜后EPBs的原因可能是由于欠屏蔽/过屏蔽电场和扰动发电机电场导致F-上升和下降导致的东/西电场波动的表现。层在倾角赤道上。有趣的是，Panhala 上空的 EPB 最初表现出向东运动，后来迅速逆转为向西运动。随着向西运动，它们也开始增长，直到 21:30 UT。然而，除了那些开始向南侧（即向赤道）下降/收缩的 EPB 外，大多数这些 EPB 都随着时间的推移而消失了。发现 EPB 的上升和收缩与赤道垂直漂移相当相关。Panhala 的 EPB 向西漂移及其与垂直漂移的反相关已从 CADI 纬向/垂直漂移中得到证实。因此，该研究还调查了风暴诱发的垂直霍尔电场作为西移的可能原因的作用及其与垂直漂移的反相关性。然而，GIRI 的观测结果并未显示今晚 Gadanki 有任何明显的向西漂移，这表明这些 EPB 的纬向漂移存在纵向梯度。除了纵向漂移逆转，纬向漂移中的纬度梯度也被注意到。目前的工作强调了风暴引起的扰动在午夜后 EPB 的产生和演化中的作用，据信这是由深低太阳极小期的弱磁扰动触发的。该研究还调查了风暴引起的垂直霍尔电场作为西移的可能原因的作用及其与垂直漂移的反相关性。然而，GIRI 的观测结果并未显示今晚 Gadanki 有任何明显的向西漂移，这表明这些 EPB 的纬向漂移存在纵向梯度。除了纵向漂移逆转，纬向漂移中的纬度梯度也被注意到。目前的工作强调了风暴引起的扰动在午夜后 EPB 的产生和演化中的作用，据信这是由深低太阳极小期的弱磁扰动触发的。该研究还调查了风暴引起的垂直霍尔电场作为西移的可能原因的作用及其与垂直漂移的反相关性。然而，GIRI 的观测结果并未显示今晚 Gadanki 有任何明显的向西漂移，这表明这些 EPB 的纬向漂移存在纵向梯度。除了纵向漂移逆转，纬向漂移中的纬度梯度也被注意到。目前的工作强调了风暴引起的扰动在午夜后 EPB 的产生和演化中的作用，据信这是由深低太阳极小期的弱磁扰动触发的。GIRI 观测结果显示，今晚 Gadanki 没有任何明显的向西漂移，这表明这些 EPB 的纬向漂移存在纵向梯度。除了纵向漂移逆转，纬向漂移中的纬度梯度也被注意到。目前的工作强调了风暴引起的扰动在午夜后 EPB 的产生和演化中的作用，据信这是由深低太阳极小期的弱磁扰动触发的。GIRI 观测结果显示，今晚 Gadanki 没有任何明显的向西漂移，这表明这些 EPB 的纬向漂移存在纵向梯度。除了纵向漂移逆转，纬向漂移中的纬度梯度也被注意到。目前的工作强调了风暴引起的扰动在午夜后 EPB 的产生和演化中的作用，据信这是由深低太阳极小期的弱磁扰动触发的。