ANALYSIS OF SPRITES FROM VIDEO OBSERVATIONS MADE BY THE CROATIAN METEOR NETWORK

Marko Šegon,Damir Šegon,Maria Vukić

doi:10.17794/rgn.2020.2.4

Abstract

Sprites are optical phenomena belonging to the category of transient luminous events. They were observed using cam- eras of the Croatian Meteor Network. The sprite images extracted from the recordings from cameras located in Rijeka and Visnjan were analysed using two methods. Sprites recorded on the night of 2017/05/31 at 21:46:18.781 and 22:03:27.299 only from the camera in Rijeka were analysed using the single-station analysis method. This method works on the as- sumption that sprites occur directly above the parent lightning and uses the lightning strike location provided by the Blitzortung website together with camera recordings from one station to make the spatial positioning of the sprite pos- sible. Sprites recorded on the night of 2017/05/31 at 21:57:44.376 and 22:07:16.440 from both cameras in Rijeka and Visnjan were analysed using the double-station analysis method, which is based on the lines of sight method. Both double-station sprites were also analysed using the single-station analysis method. The resulting heights and lateral distances were compared. It was concluded that this method of single-station analysis may provide a good estimate of the sprite location in case of small lateral distances between the sprite and parent lightning, while in other cases, errors may be significant. The double-station analysis method is preferred whenever possible, as it is mathematically exact and the errors arising from it depend only on the quality of the observation data.

Highlights

Optical phenomena that occur above the clouds during thunderstorms are called transient luminous events (TLEs)
Video samples from the Croatian Meteor Network (CMN) cameras located at Rijeka and Višnjan were used for the analysis
The program CMN_SpriteHeight_TLeSortGeocentric_AIJ was used separately for each detected sprite and the lightning detected at the corresponding time

Summary

Introduction

Optical phenomena that occur above the clouds during thunderstorms are called transient luminous events (TLEs) They are divided into several categories, characterized by their distinctive colour, shape and size. The sprite’s body is the brightest part of the sprite and previous studies have shown that above and below the body some additional features may appear such as tendrils, glows, puffs, beads and spots (Bór, 2013) Structures such as glows, beards, and spots can be found anywhere on the body of a sprite while puffs are located above and tendrils are located below the Sprites often start as one channel that later branches and, according to their final structure, they may be classified into columns, wishbones and trees, angel sprites, carrots, and other sprite forms (Bór, 2013). The most significant difference between column and carrot types is that the electric discharge fronts in column sprites propagate exclusively downwards while fronts in the

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