過往對火山閃電的研究多集中於其起電機制與煙流內部電荷結構，對其對電離層的動態影響則著墨較少。本研究旨在探討火山閃電事件和電離層電子濃度的相關性。研究利用全球導航衛星系統(GNSS)地基接收站資料計算垂直全電子含量(VTEC)，並結合全球閃電定位網之閃電資料，針對四座具代表性的火山噴發──冰島Eyjafjallajökull(2010)、智利Calbuco(2015)、瓜地馬拉Fuego(2018)與聖文森火山La Soufrière St. Vincent(2021)進行分析。
研究首先建立火山閃電判定演算法，依據空間分布和時間連續性篩選近火山口的閃電事件，並以混淆矩陣評估演算法準確度。接著以地基GNSS資料計算火山上空和參照點100 km範圍內的VTEC平均值，並計算每30秒的VTEC差值以觀察瞬時擾動。在長時趨勢方面，大型噴發事件前後之VTEC呈現明顯下降趨勢，此現象符合岩石層-大氣層-電離層耦合模型之預期，說明噴發引起的大氣電場滲透與焦耳加熱效應確實會改變電離層電子分佈。在瞬時擾動方面，火山閃電與火山上空的瞬時擾動無顯著相關，但在火山周圍則觀測到趨勢不一致的VTEC微弱擾動。此空間分佈特徵符合電磁脈衝甜甜圈狀輻射場特性。本研究嘗試釐清火山閃電對電離層擾動所扮演的角色，並解釋上升電流模型在瞬時噴發情境下並不適用。

Previous research on volcanic lightning has predominantly focused on its charging mechanisms and the internal charge structure of the plume, while its dynamic impact on the ionosphere remains insufficiently explored. This study aims to investigate the effects of volcanic lightning events on ionospheric electron density. Utilizing ground-based GNSS data to derive Vertical Total Electron Content (VTEC) and lightning data from the World Wide Lightning Location Network (WWLLN), this research analyzed four representative volcanic eruptions: Eyjafjallajökull (2010), Calbuco (2015), Fuego (2018), and La Soufrière St. Vincent (2021).
A volcanic lightning identification algorithm was first developed based on spatial distribution and temporal continuity, with its accuracy evaluated using a confusion matrix. Subsequently, mean VTEC values and 30-second VTEC differences (diff30s) were calculated to monitor instantaneous plasma disturbances. For long-term Trends, a significant decreasing trend in VTEC was observed around major eruption events. This phenomenon is consistent with the Lithosphere-Atmosphere-Ionosphere Coupling model, suggesting that atmospheric electric field penetration and Joule heating induced by the eruption significantly alter the ionospheric electron distribution. For instantaneous disturbances, no significant correlation was found between rapid VTEC fluctuations above the vent and volcanic lightning pulses. However, weak and inconsistent VTEC perturbations were observed in the surrounding areas. This spatial distribution is consistent with the donut-shaped radiation pattern of EMP from return strokes. This research tries to clarify the role of volcanic lightning in ionospheric disturbances and provides physical evidence explaining why the existing Upward Current model may not be applicable in the context of transient volcanic eruption scenarios.

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