Transpolar Arcs: Seasonal Dependence Identified by an Automated Detection Algorithm
Transpolar Arcs: Seasonal Dependence Identified by an Automated Detection Algorithm
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DOI：
10.1029/2021ja029743
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发表时间：
2021-07
期刊：
影响因子：
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通讯作者：
Gemma E. Bower;S. Milan;L. Paxton
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作者：
Gemma E. Bower;S. Milan;L. Paxton
跨极弧（TPAs）是极光的特征，发生在极光椭圆的两极，这表明磁层已经获得了一个复杂的磁拓扑结构。它们主要是一种北向行星际磁场（IMF）极光现象，其形成和演化没有一致同意的单一解释。一个自动化的检测算法已被开发来检测发生的TPA从特殊传感器紫外光谱成像仪（SSUSI）仪器机载国防气象卫星计划（DMSP）航天器上捕获的紫外图像，以进一步研究其发生。通过这种检测算法，TPA被识别为在SSUSI感测的两个或更多个波长/波段中的12.5°余纬度的极向平均辐射强度中的峰值。使用2010年至2016年的检测算法，识别出超过5000张包含TPA的图像。这些TPAs的发生显示出季节性依赖，在冬季半球可以看到更多的弧。DMSP的轨道平面已被调查的检测算法的结果的依赖性作为一种可能的解释。对于感兴趣的航天器，这导致优先观测北方半球，其中检测算法在01-06 UT左右丢失南半球的TPA。这些航天器没有发现季节性偏差。我们讨论了这些研究结果的后果，建议TPA生成机制，并建议季节性依赖的原因，包括它是一个反映的概率，看到TPA由于能见度。
Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field (IMF) auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity poleward of 12.5° colatitude, in two or more of the wavelengths/bands sensed by SSUSI. Using the detection algorithm for the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPAs shows a seasonal dependence, with more arcs being visible in the winter hemisphere. The orbital plane of DMSP has been investigated as a possible explanation of the dependences in the results of the detection algorithm. For the spacecraft of interest this leads to a preferential observation of the northern hemisphere with the detection algorithm missing TPAs in the southern hemisphere around 01–06 UT. No seasonal bias has been found for these spacecraft. We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms and suggest reasons for the seasonal dependence including it being a reflection of probability of seeing TPAs due to visibility.