Remote sensing and modeling of lightning caused long recovery events within the lower ionosphere using VLF/LF radio wave propagation

摘要

On the 4 November 2012 at 3:04:27 UT a strong lightning in the midst ofthe North Sea affected the propagation conditions of VLF/LF transmitter radiosignals from NRK (Iceland, 37.5 kHz) and GBZ (UK, 19.58 kHz) received at5246° N 8° E (NW Germany). The amplitude and phase dips show a recovery time of6–12 min pointing to a LOng Recovery Early VLF (LORE) event. Clear assignmentof the causative return stroke in space and time was possible with data fromthe WWLLN (Worldwide Lightning Location Network). Based on a return strokecurrent model the electric field is calculated and an excess electron densitydistribution which decays over time in the lower ionosphere is derived.Ionization, attachment and recombination processes are modeled in detail.Entering the electron density distribution in VLF/LF radio wave propagationcalculations using the LWPC (Long Wavelength Propagation Capability) codeallows to model the VLF/LF amplitude and phase behavior by adjusting thereturn stroke current moment. The results endorse and quantify the conceptionof lower ionosphere EMP heating by strong – but not necessarily extremelystrong – return strokes of both polarities.