Images of Sprites were captured from the ground for the first time in South Africa, the South African National Space Agency (Sansa) announced recently. Sprites are visible gas discharges triggered by lightning, but occur far above the tops of thunderstorm clouds at altitudes of between 50 km and 100 km, which last for between one and ten milliseconds. They are more formally known as transient luminous events (TLEs). Although predicted in 1925 by Prof CTR Wilson (1869–1959), who won the Nobel Prize for Physics in 1927, the first scientific observation of a TLE/Sprite only happened in 1989 and that was entirely by chance.

The first South African images were taken on January 11 by a night-vision TV camera funded by the National Research Foundation (an agency of the Department of Science and Technology). The camera is an instrument of Sansa’s Optical Space Research (OSR) Laboratory, a state-of-the-art facility hosted by the South African Astronomical Observatory at Sutherland, in the Karoo region, in terms of a four-year agreement.

Despite the fact that they must be common – they are always initiated by large cloud-to-ground lightning strikes in major thunderstorms, of which there are millions every year – they are only rarely observed. “Despite being easily visible, nobody has ever reported seeing Sprites over Southern Africa,” pointed out Sansa Hermanus office chief scientist Professor Michael Kosch. “We are extremely excited to have finally captured the first images of Sprites over South African skies.”

“These observations pave the way for more comprehensive observations at multiple wavelengths to improve our understanding of how Sprites are triggered and their effects on the upper atmosphere,” stated University of Cape Town (UCT) Department of Electrical Engineering SpaceLab Professor Peter Martinez. The images were actually captured by UCT master’s student Nnadih Stanislaus. (Martinez is his supervisor.) “It was an amazing experience – seeing in real time what has never been recorded over Southern Africa,” enthused Stanislaus. “I felt like a hunter!”

The electrical field of a thunderstorm extends upwards as well as down, and certain thunderstorms can project upwards electrical fields that are strong enough to trigger a gas discharge – a Sprite. What is striking is that thunderstorms, like nearly all weather, occur in the lowest layer of the atmosphere, the troposphere, which extends from ground level to an altitude of about 20 km. Thus, Sprites occur tens of kilometres above the storms that create them.

Sprites do not propagate upwards: they start high and propagate downwards. Large-scale TLEs, which can stretch 10 km across, can start as high as 90 km and descend to about 50 km at speeds of around 100 000 km/s. They are very bright and are characterised by vertical plasma filaments, or streamers. Yet they are rarely reported, probably because they are so brief and people tend to seek shelter during storms.

The OSR Laboratory will also be used for research into atmospheric gravity waves. “We will be using the OSR initially to study atmospheric gravity waves that will provide us with greater insight into the dynamics of the earth’s middle atmosphere,” explained Kosch. “Such knowledge is important because the middle atmosphere couples space weather from above to territorial weather below.”

Space weather is one of Sansa’s research areas. The OSR has unique capabilities that will allow the collection of critical space science data which will allow Sansa to fulfil both national and international obligations. It will also increase the standard of research in South Africa and promote scientific development, as well as provide data about currently unanswered scientific questions.