ULF electromagnetic noise from regional lightning activity: Model and observations

Contribution of lightning to geomagnetic field variations in ULF (f<1 Hz) frequency range is estimated within the framework of a simple model of ULF response to lightning strokes. ULF lightning index is introduced to quantify a contribution of lightning to ULF power at observational site. The computed pulse series are compared with the pulse-like interference recorded at the low latitude observatory (KNY). Lightning stroke is modeled as a vertical dipole with the perfectly conducting model ionosphere. A program of automatic detection of pulse-like interference in recorded signal is developed. The analysis of the time series of hourly ULF lightning index at KNY during several weeks in summer of 2012 has shown that the contribution of thunderstorms to ULF power may be significant, especially at frequencies f>80 mHz. This effect should be taken into account in any application utilizing estimates of local ULF power including seismo-electromagnetics.