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.

• 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。