Revisiting "Narrow Bipolar Event" intracloud lightning using the FORTE satellite

Abstract

Abstract. The lightning stroke called a "Narrow Bipolar Event", or NBE, is an intracloud discharge responsible for significant charge redistribution. The NBE occurs within 10-20 µs, and some associated process emits irregular bursts of intense radio noise, fading at shorter timescales, sporadically during the charge transfer. In previous reports, the NBE has been inferred to be quite different from other forms of lightning strokes, in two ways: First, the NBE has been inferred to be relatively dark (non-luminous) compared to other lightning strokes. Second, the NBE has been inferred to be isolated within the storm, usually not participating in flashes, but when it is in a flash, the NBE has been inferred to be the flash initiator. These two inferences have sufficiently stark implications for NBE physics that they should be subjected to further independent test, with improved statistics. We attempt such a test with both optical and radio data from the FORTE satellite, and with lightning-stroke data from the Los Alamos Sferic Array.We show rigorously that by the metric of triggering the PDD optical photometer aboard the FORTE satellite, NBE discharges are indeed less luminous than ordinary lightning. Referred to an effective isotropic emitter at the cloud top, NBE light output is inferred to be less than ∼3 × 10 8 W.To address isolation of NBEs, we first expand the pool of geolocated intracloud radio recordings, by borrowing geolocations from either the same flash's or the same storm's other recordings. In this manner we generate a pool of ∼2 × 10 5 unique and independent FORTE intracloud radio recordings, whose slant range from the satellite can be inferred. We then use this slant range to calculate the Effective Radiated Power (ERP) at the radio source, in the passband 26-49 MHz. Stratifying the radio recordings by ERP into eight bins, from a lowest bin (<5 kW) to a highest bin (>140 kW), we document a trend for the radio recordings to become more isolated in time as the ERP increases. The highest ERP bin corresponds to the intracloud emissions associated with NBEs.At the highest ERP, the only significant probability of temporal neighbors is during times following the high-ERP events. In other words, when participating in a flash, the high-ERP emissions occur at the apparent flash initiation.

Joint radio and optical observations of the most radio-powerful intracloud lightning discharges

“…Table 4 identifies the six events and gives the time difference (median HUMR minus PDD), which is negative because the HUMR energy-weighted center time is earlier than the PDD trigger time. It has been observed in the past that dominant strong TIPPs, corresponding to the most restrictive category in produce enough light to trigger PDD (Jacobson and Light, 2012;Light and Jacobson, 2002). Thus, the finding that six strong TIPPs are associated with measurable optical emission may not be consistent with previous findings, and thus requires examining these six events in detail.…”

“…2012) to emit much less light than do ordinary lightning discharges emitting strong VHF (Jacobson, 2003a;Light and Jacobson, 2002). Similarly, NBE strokes detected by a ground-based lightning-location array have not been detectable optically from space even when they were in view of an operating satellite-borne optical photometer (Jacobson and Light, 2012). These assertions are of course subject to the detection threshold of the photometer, discussed in detail elsewhere (Jacobson and Light, 2012;Kirkland et al, 2001).…”

“…Similarly, NBE strokes detected by a ground-based lightning-location array have not been detectable optically from space even when they were in view of an operating satellite-borne optical photometer (Jacobson and Light, 2012). These assertions are of course subject to the detection threshold of the photometer, discussed in detail elsewhere (Jacobson and Light, 2012;Kirkland et al, 2001). Nonetheless, despite this caveat, the relatively "dark" behavior of NBEs, and the associated very intense TIPPs, remains a troubling enigma in lightning science.…”

Subionospheric propagation and peak currents of preliminary breakdown pulses before negative cloud‐to‐ground lightning discharges

“…A new simple analytical model describing both bipolar and unipolar pulses was introduced by Kašpar et al, [2015]. Radio emissions associated with NBEs and other IC discharges have been detected with radio receiver on board the FORTE satellite [Light and Jacobson, 2002;Jacobson and Shao, 2002;Jacobson and Heavner, 2005;Jacobson and Light, 2012]. It was also shown that the NBE radio emission can propagate in the Earth-ionosphere waveguide and can be recorded on the ground hundreds of kilometers from the source [Smith et al, 1999].…”

“Solitary” Trans-Ionospheric Pulse Pairs onboard of the microsatellite “Chibis-M”

“…Detailed description of the project and its performance was done by, e.g. (Jacobson et al, 1999;Jacobson et al, 2000;Jacobson, 2003;Jacobson and Light, 2012). Here we would like to mention only some important features of this radio instrument.…”