地球-电离层空腔舒曼共振日变化特征分析

Diurnal variations of Schumann resonances signals in the Earth-ionosphere cavity

全球雷电活动在地球-电离层空腔中产生的极低频（ELF）信号干涉叠加,在一系列固定频率上产生舒曼共振（SR）。利用2012年5月以色列Mitzpe-Roman（MR）站ELF水平磁场资料,采用频谱变换、时间平均、分析了实测SR日变化信号的时域和频域特征。同时基于全球ELF传播模式,利用OTD/LIS雷电卫星资料模拟了5~30 Hz磁场功率谱日变化情况。结果表明：时域背景信号幅值的均值和偏差满足正态分布的期望和标准差;水平磁场前三阶SR谐振频率非常稳定,月平均下的谐振频率日变化相对8、14、20 Hz理论值的偏移量分别不超过0.3 Hz、0.55 Hz和0.6 Hz。东南亚和美洲地区雷电活动主要响应于南北磁场分量第一阶SR的07—09时和19—22时时段内。而东西磁场分量前三阶SR在12—15时时段内都对非洲地区雷电活动有指示作用。磁场功率谱日变化模拟结果与实测基本一致,表明利用单站正交磁天线的不同阶SR信号能够指示全球不同“热斑”区域的雷电活动。

With a set of distinct spectrum peaks in the extra low frequency （ELF） portion of electro- magnetic waves excited by global lightning discharges, the Schumann resonances （SR） occur. The exper- imental ELF data from Mitzpe-Roman site in Israel during May, 2012 was used to analyze the time do- main and frequency domain characteristics of diurnal variation signal of SR with methods of spectrum transform, time average. According to the ELF radio propagation model in the Earth-ionosphere cavity, the dynamic spectrum of the magnetic component of SR band was simulated by taking the OTD/LIS satel- lite lightning data as input. Results show that ELF signals in time domain follows the normal distribution very well. Compared with the theoretical values of the resonance frequencies （8, 14, 20 Hz） of the first three modes, the diurnal variations of resonance frequencies of the SR power spectrum remain stable, whose offset are less than 0.3 Hz, 0.55 Hz, 0.6 Hz, respectively. The dynamic spectrum in the ELF band shows that two power spectrum peaks appear at 07-09 and 19-22 in the fundamental SR mode for the north-south horizontal magnetic field power spectrum, produced by lightning activities in Southeast Asia and America respectively, and a sole prominent peak at 12-15 appears in the first three SR modes for the east-west horizontal magnetic field power spectrum relating to ＂Africa chimney＂. The consistency between the simulation and measurement of the diurnal variations of SR spectrum illustrates that SR is able to re- sponse to lightning activities in different areas all over the world. Lightning activities in the three ＂hot spots＂ can be monitored and be deduced timely through the signals of different SR modes received from two orthogonal magnetic antennas of individual ELF field station.