Rain. Clouds. Thunder. There is none of this in the stratosphere. The weather is pretty boring there. Except when lightning starts to flash … Researchers call them "blue streams." These elusive discharges slip into the stratosphere from lightning discharges far below.
They are rarely seen, but storm hunter Rob Neep was able to capture several of them over Sonora, Mexico on August 3:
"I couldn't believe my eyes," says Nip, a former television journalist. "I was really looking for sprites when the jets appeared. They were definitely visible to the naked eye, and I and my cousin watched them."
Oscar van der Velde of the Lightning Research Group at the Polytechnic University of Catalonia watched Neep's video and said it was "excellent - perhaps the best example of classic blue jets we've seen in a long time!"
First captured by cameras on the space shuttle in 1989, the blue jets are part of a growing family of transient luminous phenomena (TSS) in the upper atmosphere. They appear alongside sprites, elves, and other lightning-like forms. However, blue jets seem more elusive than others and are often disappointing for photographers trying to catch them.
"We're not sure why ground-based observers see them so rarely," says van der Velde. "Perhaps it has something to do with their blue color. Earth's atmosphere naturally scatters blue light, making them harder to see. Perhaps blue jets are much more common than we think."
In 2018, SpaceX launched the European Atmospheric Space Interaction Monitor (ASIM) to the International Space Station to study TLEs from space. Data from ASIM show that blue jets can sweep up to 52 km above the ground. They arise from mysterious "blue explosions" - bright blue flares at the tops of thunderclouds, possibly caused by severe turbulence.
Studying blue streams is important because, according to van der Velde, "these emissions can result in significant production of NOx and ozone, potentially affecting the chemical composition of the atmosphere".
Besides, some blue jets can rise high enough to affect the ionosphere, forming a new and poorly understood branch of the global electrical circuit.