25～100MHz频段闪电脉冲辐射能量频谱特征

LIGHTNING ELECTROMAGNETIC RADIATION FIELD SPECTRA IN THE INTERVAL FROM 25 TO 100 MHz

对闪电不同放电过程中辐射能量频谱特征的观测分析结果表明,经25 MHz高通滤波器对闪电辐射能量的低频成分抑制后,所得到闪电不同放电过程期间的宽带辐射信号,其能量谱分布有较大的差异.在25~100 MHz频段内,地闪较低频段的辐射强于云闪;云闪、地闪预击穿过程和K变化过程峰值辐射能量处于相对较高的频段,表明这些过程可能以较小尺度的放电为主要特征;梯级先导和直窜先导过程初始阶段辐射能量主要集中在较高频段,而接近地面时则集中在较低频段,表明先导在向地面发展过程中放电尺度逐渐增大.

Average energy spectra are presented for most of components from lightning by recording the transient radiation with a wide bandwidth device and then Fourier transforming the waveform to obtain a spectrum. Holding back the low frequency signals through the 25 MHz high pass filters, the shapes of the different discharge processes spectra from lightning are obvious dissimilar in the interval from 25 to 100 MHz. Radiation from the cloud-to-ground lightning is stronger in the lower frequency range than intracloud lightning; Average power spectra peaks near 60~70 MHz, a relatively high frequency band, for cloud lightning, preliminary breakdown and intracloud K changes of cloud-to-ground lightning, indicating that the relative smaller size of discharge is characteristic of these components; During the stepped and dart leader propagating from cloud to ground, the peak frequency band of the average energy spectra reduces from high to low frequency band, indicating that the size of the breakdown is increased gradually.