Lightning Charge Moment Change and High Altitude Effects

Lightning can generate spectacular high altitude effects---among them sprites, gigantic jets, and terrestrial gamma-ray flashes.  When first discovered, the physics of these phenomena and the details of their connection to lightning were unknown.  Gaining some understanding required quantitative measurements of the driving lightning.  Although many of these phenomena are not uncommon, they are produced only by a small fraction of lightning flashes.  Rarely is the right kind of lightning in the right place at the right time to make detailed, local measurements.

Consequently, progress in the field has relied heavily on remote (often thousands of km distant) measurements of electromagnetic fields produced by the source lightning and, in some cases, the high altitude phenomenon itself.  In this presentation, we will summarize recent research in which remote radio measurements, spanning a wide range of timescales that are dictated by the phenomena of interest, were used to measure different lightning processes in order to better understand how these effects are created by lightning.  Specific topics that will be covered are the lightning flash development that produces gigantic jets and the charge motion in the jet itself; the relationship between sprite location, the underlying lightning flash structure, and the cloud-to-ground charge transfer; and the lightning flash structure and charge motion behind terrestrial gamma-ray flashes.  We will also discuss efforts to develop systems to automatically measure lightning charge moment change, and the scientific results that have emerged.