Optical and radio frequency direction-analysis of a dancing sprite

Sprites are upper atmospheric lightning phenomena that are known for their fleeting nature, red color and interesting morphology. They are most commonly generated by upper atmospheric discharges caused by strong positive cloud-to-ground lightning. This study aims to find the direction of arrival of a dancing sprite observed during the sprite campaign in South Africa 2023, using both radio measurements and optical images. The campaign of 2023 had one optical measurement station and three electromagnetic stations. The electromagnetic stations could receive horizontal signals in both the north-south and east-west directions. Determining the direction of arrival using radio measurements of the electric and magnetic fields associated with an event of interest is not a novelty and is commonly used in lightning detection networks. The novelty in this project is using radio measurements to determine the direction of arrival of a sprite, together with the verification of the well-established method of star-fitting to obtain the azimuth direction to the sprite using the optical images. The method of star-fitting uses the known positions of stars in the sky to overlay the image of a sprite with visible stars with plotted stars to obtain an accurate azimuth and elevation position of the sprite.
 
The results of the star-fit gave an approximate direction to the sprite in the north-east east (NEE) direction, which coincides to a certain degree of accuracy with the results from the radio data processing. The results also show a large displacement between the parent lightning and the sprite which is rare and indicates a large horizontal current during the storm. In future campaigns, setting up the stations further apart could open up the possibility for accurate time-of-arrival analysis, which would give a result comparable to lightning detection networks. Further, if all stations would be equipped with three orthogonal electric and three orthogonal magnetic field receivers, a more reliable result could be ensured.