 |
| Titel |
Revisiting "Narrow Bipolar Event" intracloud lightning using the FORTE satellite |
| VerfasserIn |
A. R. Jacobson, T. E. L. Light |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 2 ; Nr. 30, no. 2 (2012-02-24), S.389-404 |
| Datensatznummer |
250017187
|
| Publikation (Nr.) |
 copernicus.org/angeo-30-389-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
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 × 108 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 × 105 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. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|