Lightning transient fields in the atmosphere—low ionosphere

The complexity of the electric properties of the atmosphere, which influences the excitation and propagation of electromagnetic signals generated by lightning discharges, gives rise to a diversity of the typical signal wave forms and amplitudes in the various space-time domains. This causes difficulties and controversies in the interpretation of the experimental data. In geophysical problems of such a kind, considerations accounting for a broadband spectrum are particularly important.

In the present paper, lightning induced ULF-VLF fields in the daytime inhomogeneous atmosphere and D-region of the ionosphere above the thundercloud are analyzed for a standard model of the vertical return stroke. The developed analytical approach makes it possible to unite the canonical model of the electromagnetic radiation into a free-half-space, the discharge (ELF-VLF spectrum) and ‘post-discharge’ (ULF spectrum) low-frequency models and to clarify the temporal scales in the mechanism of lightning coupling with the atmosphere and low ionosphere with respect to the local relaxation time, discharge characteristic time scales and observer location.