CEDAR: Characterization of Streamer-based Compact Intracloud Discharges (CIDs, aka NBEs)

University Of Florida, Gainesville FL

Investigators

Abstract

The research seeks funds to study in detail the enigmatic compact intracloud lightning discharges (CIDs) that are triggered at higher altitudes (e.g., in convective surges penetrating into the stratosphere) by energetic (>1016 eV) cosmic ray showers (CRSs). CIDs are known to be the strongest natural producers of VHF radiation on Earth. Most CIDs are solitary, some serve to initiate ordinary lightning, and some occur in clusters. They were discovered in 1980, but their nature largely remains a mystery, because they are brief, hidden inside the cloud, and usually produce no detectable visible light. One of the objectives of the suggested work is to solve the inverse problem to separately obtain, for the first time, the CID current and CID channel length from calibrated multiple-station electric field measurements. Expected results have important implications for our basic understanding of non-conventional (streamer-based) lightning phenomena and energy coupling between the different layers of Earth’s atmosphere. The project outcomes will be also useful in a number of other disciplines, including atmospheric electricity, high-energy atmospheric physics, meteorology, lightning detection, and plasma physics. The studies will serve to foster international collaboration and involves participation of graduate students. The projects will address new science questions that are relevant to the primary objective of the CEDAR Program, which is “to understand changes in the atmosphere over short- and long-time scales” and are: (a) What are the electric parameters of CIDs, including currents and charge transfers? (b) Can a large, low-conductivity (essentially cold) streamer formation that constitutes the body of CID support traveling waves? (c) What is the largest altitude at which CIDs occur and what is the origin of post-CID activity? This effort will lead to acquisition of a large data set, compare three different methods for estimating CID heights and search for “outliers” to investigate events that occur above the average height. The researchers plan to study the recently discovered secondary pulses that follow the main CID waveform attributed to the so-called blue events (BLUEs) at cloud tops. Success will be primarily gauged by publications, presentations at conferences, graduate degrees awarded, and high-school and undergraduate students involved. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.