The Fly's Eye:
Fast Photometry of Sprites and Elves

INTRODUCTION BACKGROUND INSTRUMENT DESIGN ANALYSIS TOOLS
1996 RESULTS 1997 FIELD WORK 1998 FIELD WORK PUBLICATIONS

Introduction

The Fly's Eye is an array of photomultipier tubes designed to time-resolve the horizontal development of intense sub-millisecond ionospheric flashes that have come to be known as "elves". The Fly's Eye was built at Stanford University and deployed during the 1996 Sprites Campaign, and the data below were collected from Yucca Ridge Field Station near Fort Collins, Colorado, during July, 1996.

Background

"Elves" are transient luminous events in the lower ionosphere produced by nitrogen fluorescence due to electromagnetic pulses (EMPs) from intense return strokes of lightning discharges.

You can see the predicted [Glukhov and Inan, 1996] intensity of this discharge in a simulation, below. The geometry of the viewing position is indicated in the figure below: The perspective is from 250 km away from the causative lightning discharge, and looks up with a vield of view 66 degrees wide and 36 degrees high. The center of the image in the video corresponds to an altitude of 125 km directly over the lightning, and the video shows the discharge evolve over about a millisecond. Click on the icons to expand or play them.
elf250.mpg [0.377 MB]
There is also a 1MB movie and the corresponding time-integrated image that corresponds to what a video camera might see. This scenario is similar, but the causative lightning is 600 km away and the field of view is 52 degrees in the horizontal direction and 20 degrees in the vertical direction. The bottom row of the frame corresponds to the horizon. There are 256 frames in the movie. The time interval between the frames is 10 microseconds, so that the whole movie is 2.56 milliseconds long.

Alternatively, you can view these snapshots of what an elf would look like from the ground from two different distances:

The last snapshots are integrated over the 33 ms of a video field, so these represent the expected video signature of elves.

References

Glukhov, V. S., and U. S. Inan, Particle simulation of the time-dependent interaction with the ionosphere of rapidly varying lightning EMP, Geophys. Res. Lett., 23, 16, 1996.

Fukunishi, H. Y., Y Takahashi, M. Kubota, K. Sakanoi, U. S. Inan and W.A. Lyons, Elves: Lightning-induced transient luminous events in the lower ionosphere, Geophys. Res. Lett., 23, 2157, 1996.

Inan, U.S., W.A. Sampson and Y. N. Taranenko, Space-time structure of optical flashes and ionization changes produced by lightning-EMP, Geophys. Res. Lett.,23 ,133 , 1996.

Inan, U. S., C. Barrington-Leigh, S. Hansen, V. S. Glukhov, and T. F. Bell, Rapid Lateral Expansion of Optical Iuminosity in Lightning-Induced Ionospheric Flashes Referred to as 'Elves', Geophys. Res. Lett., 24, 583, 1997.

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