One of the biggest mysteries in lightning science is the Narrow Bipolar Event (NBE), a rapid intracloud charge transfer. Its physics remains enigmatic, because the NBE: (a) lacks readily detectable light output, unlike all other known lightning of comparable current; (b) lacks any detectable channel-preparation (leader) process, again unlike all other known lightning strokes; and (c) radiates the most powerful High-Frequency (HF) and Very-High-Frequency (VHF) emissions compared with those of any lightning.
Intellectual merit. This study will investigate the properties of NBEs using both satellite- and ground-based observational data. In particular, the project involves analyzing polarization and spectral information in the data by studying all VHF events. The research will improve current understanding of the physics of NBEs, and may advance our knowledge on lightning initiation processes.
Broader impacts. The remote sensing of lightning from space is an important proxy for monitoring convective weather processes. Detecting and understanding of intracloud charge transfer may improve prediction of severe weather. The research may also shed light on lightning initiation processes, terrestrial gamma ray flashes, or any other types of unusual discharges in the atmosphere. A graduate student will be trained in this subject area as well.
" was undertaken by researchers Abram R. Jacobson and Robert Holzworth at the University of Washington. The project title implies the basic fact about this surprising form of lightning, that it emits very little visible light compared to ordinary lightning. (In fact, reflect a bit about the word "lightning". What is the implied essential characteristic? Light!) Our goal in this work was to quantify the light output of a special form of lightning known as "Narrow Bipolar Events", or "Compact Intracloud Discharges". These occur only within a thundercloud, never below the cloud and never at the ground. The Narrow Bipolar Event is an electrical discharge which allows opposite charges in different regions of the cloud to surge toward each other and cancel the charge separation. Our principal data-gathering tool was the FORTE satellite, a small research satellite launched in 1997 with the mission of recording the optical and radio emissions of lightning. FORTE was an ideal platform for this study, because it could address the key question of the ratio of optical to radio power from Narrow Bipolar Events and from ordinary lightning. We were able to set an upper limit of the light output based on our optical-detection sensitivity. This outcome will assist physicists seeking to devise better models of the internal physics of the Narrow Bipolar Event discharge.
