Observation of local and conjugate ionospheric perturbations from individual oceanic lightning flashes

Abstract

Very low frequency (VLF) remote sensing observations of multifaceted local and conjugate ionospheric perturbations from geographically identified and well‐characterized oceanic lightning discharges are presented for the first time. Lightning‐induced electron precipitation (LEP) events are shown to produce disturbances first in the conjugate hemisphere and subsequently in the hemisphere of the causative lightning discharge in agreement with theoretical predictions. A rough threshold peak current of ∼100 kA is identified for lightning discharges to generate LEP events for the geomagnetic conditions present during observations. The occurrence of early VLF events and the subsequent duration of their recovery do not seem to fit any simple metric of lightning discharge peak current or proximity to great circle path. Knowledge of the full spectral density of the lightning electromagnetic pulse, not just its peak current, and the subionospheric mode structure are likely necessary to determine if a specific lightning discharge will generate an early VLF perturbation.

On the Use of VLF Narrowband Measurements to Study the Lower Ionosphere and the Mesosphere–Lower Thermosphere

“…Among different topics regarding the LEP, these questions were focused on the electron precipitation flux intensity based on the LEP driven VLF perturbation amplitudes [e.g., Inan et al, 1985b;Tolstoy et al, 1986;Inan and Carpenter, 1987;Clilverd et al, 2004], the LEP event sources and mechanisms [e.g., Inan et al, 1988b;Burgess and Inan, 1990;Dowden and Adams, 1990;Poulsen et al, 1993;Clilverd et al, 2004;Peter and Inan, 2004;Gołkowski et al, 2014], and the precipitating electron energies [e.g., Helliwell et al, 1973;Lohrey and Kaiser, 1979;Inan et al, 1988a].…”

“…In addition, they concluded that LORE occurrence strongly favors powerful CG discharges with peak currents above ±250 kA (which accounts for less than 0.5% of the total number of lightning discharges), thereby explaining some of the observations made by Haldoupis et al [2012]. Nevertheless Salut et al [2013] and Gołkowski et al [2014] have shown that the induced LORE amplitudes were not directly related to the peak current strength and proximity to the TRGCP, and that in more than 75% of their occurrence, these VLF disturbances are produced by positive lightning discharges. Moreover, NaitAmor et al [2013] have concluded that the occurrence of LOREs mainly depends on the modal structure of the VLF signal, the VLF NB scattering process, and the distance of the transmitter and receiver from the disturbed region, while the occurrence of TLEs and the lightning peak current only play a secondary role.…”

Quantification of Ionospheric Perturbations From Lightning Using Overlapping Paths of VLF Signal Propagation

“…Specifically, we note that Salut et al. (2013) found that large peak current lightning can cause early/fast VLF perturbations up to 400 km away and observations and models show lateral perturbation dimensions for LEP events of up to 1,000 km (Clilverd et al., 2002; Gołkowski et al., 2014; Inan & Carpenter, 1987). We acknowledge that it is impossible to specify the radius of each of these disturbances, so we evaluate the effect of this assumed radius size in Section 4.1.…”

“…For early/fast events we assume a 200 km radius centered on the lightning location for the dynamic region and for LEP events we assume a 400 km radius. These assumed dimension are based on estimates given in past work (Clilverd et al., 2002; Gołkowski et al., 2014; Haldoupis et al., 2004; Inan et al., 2010; Salut et al., 2013) and we have taken the upper bound of past estimates since we are modeling the effects of large peak current lightning events. Specifically, we note that Salut et al.…”

“…These assumed dimension are based on estimates given in past work (Clilverd et al, 2002;Gołkowski et al, 2014;Haldoupis et al, 2004;Inan et al, 2010;Salut et al, 2013) and we have taken the upper bound of past estimates since we are modeling the effects of large peak current lightning events. Specifically, we note that Salut et al (2013) found that large peak current lightning can cause early/ fast VLF perturbations up to 400 km away and observations and models show lateral perturbation dimensions for LEP events of up to 1,000 km (Clilverd et al, 2002;Gołkowski et al, 2014;Inan & Carpenter, 1987). We acknowledge that it is impossible to specify the radius of each of these disturbances, so we evaluate the effect of this assumed radius size in Section 4.1.…”