Heating of the nighttime D region by very low frequency transmitters
Heating of the nighttime D region by very low frequency transmitters
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DOI：
10.1029/94ja02001
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发表时间：
1994-12
影响因子：
--
通讯作者：
Juan V. Rodriguez;U. Inan;T. Bell
中科院分区：
文献类型：
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作者：
Juan V. Rodriguez;U. Inan;T. Bell
在地球电离层波导中传播的VLF信号被用于通过三个美国海军甚低频（VLF，3-30 kHz）发射机探测夜间加热的D区域。当发射机在正常运行过程中关闭和打开时，观测到电离层冷却和加热。1992年12月期间，在52个关/开事件中的41个事件中，用这种方法观察到缅因州卡特勒的24.0-kHz NAA发射机（1000 kW辐射功率）的加热，使从马里兰州的安纳波利斯传播到纽芬兰的甘德的21.4-kHz NSS探测波的振幅增加0.84 dB，相位延迟5.3°。在这41次发作中的6次中，从波多黎各传播到甘德的28.5 kHz NAU探头波的振幅也受到了高达0.29 dB的扰动。由于NAA和NAU-Gander大圆路径之间的距离超过770公里，后面的观测结果是意外的，NSS（21.4 kHz，265 kW）和NLK（24.8 kHz，850 kW）发射机的加热是在早期测量地球电离层波导中传播的甚低频信号幅度的数据中偶然观察到的。在磁化的弱电离等离子体中的波吸收和电子加热的三维模型用于计算碰撞频率的范围和形状（即，电子温度）增强。增强是环形的，具有地磁南北不对称性，碰撞频率增强的外半最大半径约为150公里。加热的NAA发射机预计将增加夜间D区电子温度多达3倍。计算的D区域电导率的变化中使用的三维模型中的地球电离层波导中的传播，以预测亚电离层甚低频探测波的加热补丁的效果。预测的散射场振幅的范围通常与观察到的信号扰动一致。预测中的不一致性归因于缺乏沿探测波大圆路径沿着的D区电子密度分布的知识。
VLF signals propagating in the Earth-ionosphere waveguide are used to probe the heated nighttime D region over three U.S. Navy very low frequency (VLF, 3-30 kHz) transmitters. Ionospheric cooling and heating are observed when a transmitter turns off and on in the course of normal operations. Heating by the 24.0-kHz NAA transmitter in Cutler, Maine, (1000 kW radiated power) was observed by this method in 41 of 52 off/on episodes during December 1992, increasing the amplitude and retarding the phase of the 21.4-kHz NSS probe wave propagating from Annapolis, Maryland, to Gander, Newfoundland, by as much as 0.84 dB and 5.3°, respectively. In 6 of these 41 episodes, the amplitude of the 28.5-kHz NAU probe wave propagating from Puerto Rico to Gander was also perturbed by as much as 0.29 dB. The latter observations were unexpected due to the > 770 km distance between NAA and the NAU-Gander great circle path. Heating by the NSS (21.4 kHz, 265 kW) and NLK (24.8 kHz, 850 kW) transmitters was observed serendipitously in data from earlier measurements of the amplitudes of VLF signals propagating in the Earth-ionosphere waveguide. A three-dimensional model of wave absorption and electron heating in a magnetized, weakly ionized plasma is used to calculate the extent and shape of the collision frequency (i.e., electron temperature) enhancement above a VLF transmitter. The enhancements are annular, with a geomagnetic north-south asymmetry and a radius at the outer half-maximum of the collision frequency enhancement of about 150 km. Heating by the NAA transmitter is predicted to increase the nighttime D region electron temperature by as much as a factor of 3. The calculated changes in the D region conductivity are used in a three-dimensional model of propagation in the Earth-ionosphere waveguide to predict the effect of the heated patch on a subionospheric VLF probe wave. The range of predicted scattered field amplitudes is in general consistent with the observed signal perturbations. Discrepancies in the predictions are attributed to lack of knowledge of the D region electron density profile along the probe wave great circle paths.