Free-running ground-based photometric array imaging of transient luminous events

Abstract

We present observations of transient luminous events (TLEs) recorded during a summer TLE observation campaign in 2008 at Langmuir Laboratory near Socorro, New Mexico. The campaign featured observations made by a free-running, ground-based multianode photometric array called the Photometric Imager of Precipitated Electron Radiation (PIPER). As a photometric array, PIPER has high (40 mu s) temporal resolution and enough spatial resolution (16 anodes per photometer) to make it particularly useful in the study of fast TLEs like elves and halos. As a free-running instrument, there are no missed detections and no unwanted sampling bias introduced by triggering. As a ground-based instrument, it can follow individual storms over the course of their lifetime rather than randomly sampling over large numbers of storms as required by space-based instruments. During the campaign, 143 sprites, 803 elves, and 166 halos were observed over six storms, resulting in averaged elve-to-sprite and halo-to-sprite occurrence ratios of 5.6:1 and 1.2:1, respectively. There was considerable variability in the elve-to-sprite occurrence ratio from storm to storm, ranging from a low of 3.7:1 to a high of 13.4:1. Overall, 78.2% of the elves and 55.4% of the halos were associated with negative cloud-to-ground lightning strikes (-CGs); no sprites associated with -CGs were observed. Additionally, 40 events in which pairs of elves occur in rapid succession, events we refer to as elve doublets, were observed in several storms. The duration between elves in the elve doublet events was typically 120 mu s. The causative mechanism for these events is still under deliberation.