A. Luque & U. Ebert, Nature Geosci., Emergence of sprite streamers from screening-ionization waves in the lower ionosphere

Nature Geoscience, 2 (2009) 757-760; published online 25 October 2009; doi: 10.1038/ngeo662

Emergence of sprite streamers from screening-ionization waves in the lower ionosphere

Alejandro Luque¹ and Ute Ebert^1,2

Abstract

Sprite discharges above thunderclouds at altitudes of 40–90 km (refs 1, 2, 3, 4, 5) are usually created by a strong positive cloud-to-ground lightning flash⁶. Sometimes these sprite discharges emerge from a visible halo^{5, 7, 8, 9}, and during the first stage they always propagate downwards and branch on their way^{5, 7, 9, 10, 11}. Modelling efforts have been restricted to conditions of non-ionized air of constant density and show double-headed sprites¹² or sprites starting from metal electrodes, but they do not explain why observations exclusively record sprites that propagate downwards. Here we present simulations with a numerical discharge model on a non-uniform, dynamically adapted computational grid¹³ to capture the wide range of emerging spatial scales, and we use realistic air and electron densities that vary with altitude. Our model shows a downward-propagating screening-ionization wave in the lower ionosphere that sharpens and collapses into a sprite streamer as it propagates farther down. Streamer velocity, diameter and length until branching agree with observations⁹ within measuring accuracy. We speculate that sprites generically emerge through the collapse of a wide screening-ionization wave into a sprite streamer, although this wave is only sometimes visible as a luminous halo.

¹Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090 GB Amsterdam, The Netherlands
²Department of Applied Physics, Eindhoven University of Technology, The Netherlands

Correspondence to: Alejandro Luque¹ e-mail: luque@cwi.nl

Correspondence to: Ute Ebert^1,2 e-mail: ebert@cwi.nl