VLF Imaging of Lightning-Induced Disturbances of the Lower Ionosphere

一项在美国多个地点进行甚低频(VLF)观测的三年计划被提出，目的是对与闪电发射相关的电离层扰动进行‘成像’。第一年的实验涉及在波多黎各、亨茨维尔、学院公园、休斯顿和斯坦福测量甚低频发射机信号的幅度和相位，提供了一个横跨大陆的大圆路径网格。瞬变电离层扰动的位置是通过在交叉和共线VLF路径上同时发生来确定的。闪电诱发的电离层扰动事件是根据其特征特征识别的，发生的原因是：(1)闪电诱发的高能粒子从辐射带沉淀，(2)闪电辐射直接向上耦合到低电离层，产生强烈的加热和电离。第二年的计划涉及在阿拉巴马州亨茨维尔附近的五个紧密间隔的地点进行测量，目的是在紧密(但不规则)的路径网格上进行断层成像。拟议的测量计划协同受益于斯坦福大学在南极洲帕尔默的观测和最近开发的甚低频在地球-电离层波导中传播的三维模型。第三年观测方案强调对已知雷暴活动的美国西南部和中南部地区的事件发生情况进行测量。

A three year program of very low frequency (VLF) observations at multiple sites across United States is proposed for the purpose of 'imaging' ionospheric disturbances that occur in association with lightning discharges. The first year experiment involves measurement of amplitude and phase of VLF transmitter signals at Puerto Rico, Huntsville, College Park, Houston and Stanford, providing a grid of great circle paths over the continent. The location of transient ionospheric disturbancesare determined by means of simultaneous occurrences on crossing and collinear VLF paths. The lightning-induced ionospheric disturbance events are recognized on the basis of their characteristic signatures and occur due to (i) lightning-induced precipitation of energetic particles from the radiation belts, and (ii) direct upward coupling of lightning radiation to the lower ionosphere producing intense heating and ionization. The second year program involves measurements at five closely spaced sites in the vicinity of Huntsville, Alabama for the purpose of tomographic imaging on a tight (but irregular) grid of paths. The proposed measurement program synergistically benefits from Stanford observations at Palmer, Antarctica and a recently developed three dimensional model of VLF propagation in the earth-ionospherewaveguide. The third year observation program emphasizes measurement of event occurence in the south western and south-cenbtral United States region of known high thunderstorm activity.