Abstract. Electric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit order-of-magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure; knowing their true magnitude and temporal variability is important for a theoretical understanding of auroral processes. We present a unique method to estimate ionospheric electric fields in the region close to (kilometre scale) a dynamic auroral arc by solving the continuity equation for the metastable O+(2P) ions, which emit as they move under the influence of electric fields during their 5 s lifetime. The main advantage of this optical method is the increase in temporal resolution over other methods such as ground-based radars. Simultaneous measurements of emission at 732.0 nm (from the O+(2P) ions) and prompt emissions at 673.0 nm ( N2 ) and 777.4 nm (O), all at high spatial (100 m) and temporal (0.05 s) resolution, are used in the solution of the continuity equation, which gives the dynamic changes of the O+ ion population at all heights in a 3D volume close to the magnetic zenith. Perspective effects are taken into account by a new geometric method, which is based on an accurate estimate of the magnetic zenith position. The emissions resulting from the metastable ions are converted to brightness images by projecting them onto the plane of the ground, and the projected images are then compared with the measured images. The flow velocity of the ions is a free parameter in the solution of the continuity equation; the value that minimises the difference between the modelled and observed images is the extracted flow velocity at each time step. We demonstrate the method with an example event during the passage of a brightening arc feature, lasting about 10 s, in which the inferred electric fields vary between 20 and 120 mV m −1 . These inferred electric fields are compared with SuperDARN measurements, which have an average value of 30 mV m −1 . An excellent agreement is found in the magnitude and direction of the background electric field; an increase in magnitude during the brightening of the arc feature supports theories of small-scale auroral arc formation and electrodynamics.

中文翻译：

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亚秒时间分辨率下极光 O⁺(²P) 离子流的水平电场

摘要。电场是电离层的一个普遍特征，通过粒子降水和场对齐电流与极光密切相关。它们分别在秒和公里的时间和空间尺度上表现出数量级的变化，不易测量；了解它们的真实幅度和时间变化对于从理论上理解极光过程很重要。我们提出了一种独特的方法，通过求解亚稳态 O+(2P) 离子的连续性方程来估计接近（公里尺度）动态极光弧区域的电离层电场，这些离子在电场的影响下移动时发射。 5 s 寿命。这种光学方法的主要优点是相对于其他方法（如地基雷达）的时间分辨率有所提高。同时测量 732.0 nm 的发射（来自 O+(2P) 离子）和 673.0 nm (N2) 和 777.4 nm (O) 的瞬发发射，均采用高空间 (100 m) 和时间 (0.05 s) 分辨率在连续性方程的解中，它给出了接近磁顶点的 3D 体积中所有高度的 O+ 离子群的动态变化。一种新的几何方法考虑了透视效应，该方法基于磁天顶位置的准确估计。亚稳态离子产生的发射通过将它们投影到地面上而转换为亮度图像，然后将投影图像与测量图像进行比较。离子的流速是连续性方程解中的一个自由参数；最小化建模图像和观察图像之间差异的值是每个时间步长的提取流速。我们通过亮弧特征通过期间的示例事件来演示该方法，持续约 10 秒，其中推断的电场在 20 到 120 mV m -1 之间变化。这些推断的电场与 SuperDARN 测量值进行比较，后者的平均值为 30 mV m -1 。在背景电场的大小和方向上发现了极好的一致性；电弧特征变亮期间幅度的增加支持了小尺度极光电弧形成和电动力学的理论。持续大约 10 秒，其中推断的电场在 20 到 120 mV m -1 之间变化。这些推断的电场与 SuperDARN 测量值进行比较，后者的平均值为 30 mV m -1 。在背景电场的大小和方向上发现了极好的一致性；电弧特征变亮期间幅度的增加支持了小尺度极光电弧形成和电动力学的理论。持续大约 10 秒，其中推断的电场在 20 到 120 mV m -1 之间变化。这些推断的电场与 SuperDARN 测量值进行比较，后者的平均值为 30 mV m -1 。在背景电场的大小和方向上发现了极好的一致性；电弧特征变亮期间幅度的增加支持了小尺度极光电弧形成和电动力学的理论。