Substorm correlated absorption on a 3200 km trans-auroral HF propagation path
Substorm correlated absorption on a 3200 km trans-auroral HF propagation path
复制标题
3200 公里跨极光高频传播路径上的亚暴相关吸收
DOI：
10.1007/s00585-996-0182-8
复制
发表时间：
1996
影响因子：
1.9
通讯作者：
G. Reeves
中科院分区：
文献类型：
--
作者：
S. Milan;T. Jones;M. Lester;E. M. Warrington;G. Reeves
位于加拿大西北部克莱德河的高频发射机和位于美国波士顿附近的接收机提供了一条3200公里的跨极光近子午线传播路径，通过该路径测量了传播特性。在实验期间(1989年1月16日至2月8日)，从高频波段每小时采样的14个频率中，选择了6.800兆赫传输的信号电平测量值，以确定极光吸收的程度和发生情况。沿途极光吸收的中位数水平被发现随着地磁活动而增加，由指数Kp量化，午夜后区段的增加幅度大于午夜前区段。这种不对称行为归因于将高能电子沉淀到午夜和早晨的极光D区。测量到的吸收中值水平的日变化与以前描述极光吸收和电子沉淀的范围和大小的模型一致。从地球同步卫星数据中确定的个别亚暴在6.800兆赫的高频信号水平上造成短暂的吸收事件。与亚暴相关的极光吸收事件的发生仅限于午夜和早晨，这与电子降水的位置一致。吸收的大小与亚暴发展阶段的磁尾应力和亚暴扩展阶段开始时的磁尾弛豫有关。运动期间的吸收强度和亚暴的发生在Kp高的时候增加，导致扰动期间极光吸收的中位数增加。
A high-frequency transmitter located at Clyde River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km trans-auroral, near-meridional propagation path over which the propagation characteristics have been measured. Out of the fourteen frequencies in the HF band sampled every hour for the duration of the experimental campaign (16 January-8 February 1989), the signal level measurements of 6.800 MHz transmissions were selected in order to determine the extent and occurrence of auroral absorption. The median level of auroral absorption along the path is found to increase with geomagnetic activity, quantified by the index Kp, with the increase being greater in the post-midnight sector than in the pre-midnight sector. This asymmetric behaviour is attributed to the precipitation of high energy electrons into the midnight and morning sector auroral D region. The measured diurnal variation in the median level of absorption is consistent with previous models describing the extent and magnitude of auroral absorption and electron precipitation. Individual substorms, identified from geosynchronous satellite data, are found to cause short-lived absorption events in the HF signal level of \sim30 dB at 6.800 MHz. The occurrence of substorm correlated auroral absorption events is confined to the midnight and morning sectors, consistent with the location of the electron precipitation. The magnitude of absorption is related to the magnetotail stress during the substorm growth phase and the magnetotail relaxation during the substorm expansion phase onset. The absorption magnitude and the occurrence of substorms during the period of the campaign increase at times of high Kp, leading to an increase in median auroral absorption during disturbed periods.