Experiencing thunderstorms on Earth is yesterday's news. The future of thunderstorms is in space.
The European Atmosphere-Space Interactions Monitor (ASIM) observatory onboard the International Space Station (ISS) is tasked with observing the phenomena linked to thunderstorms — strange, poorly understood features like elves, sprites, and blue jets.
This unique view of the brewing storms provides new insights into weather on Earth. On Wednesday, in first for an ESA ISS experiment, observations were published in the journal Nature. Blue jets — electric discharges that propagate from the top of thunderstorms into the stratosphere — generate "fantastic sounding" elves (rings of optical and UV emissions), the study finds. These jets begin as flashes in cloud top.
The study is one of the most detailed and accurate looks at thunderstorms to date — and more observations are underway.
How do thunderstorms form?
Our Sun heats the surface of the Earth, causing the air in the planet's lower atmosphere to become warmer. As the warm, moist air rises to colder regions of the Earth's atmosphere, transferring the heat from the surface of the Earth to the upper layers of the atmosphere.
The moisture contained within the air, or water vapor, starts to cool and condenses to form a cumulus cloud.
The cloud continues to rise to areas of the atmosphere where the temperatures are freezing. The collision between the warm and cold air masses builds up an electrical charge, which eventually causes thunder and lightning.
Seeing thunderstorms from space — The ISS orbits Earth at a distance of around 200 miles above.
Onboard the spacecraft, the ASIM observatory has optical cameras, photometers, and an X- and gamma-ray detector. These tools are used to look down at Earth's stormy weather and capture thunderstorms as they erupt in the planet's atmosphere.
The observations described in the Nature study required the observatory's instruments to capture lightning in clouds. This lighting, in turn, was followed by a blue flash that lasted for 10 microseconds, a blue jet lasting 400 milliseconds, and an elve generated by the blue flash that lasted for 30 microseconds.
These weather phenomena were only discovered in the 1990s, and are very difficult to observe from Earth.
Elves are rapidly expanding rings of optical and ultraviolet emissions at the bottom of the ionosphere, the ionized part of Earth's upper atmosphere. In the ionosphere, electrons and radio waves interact to form these emissions.
Meanwhile, a blue jet is a form of lightning that shoots upwards from thunderstorm clouds, usually lasting for less than a second.
By capturing the thunderstorms from above the Earth, scientists get a rare view of what's going on right above our heads but often hard for us to see.
"This paper is an impressive highlight of the many new phenomena ASIM is observing above thunderstorms and shows that we still have so much to discover and learn about our Universe," Astrid Orr of the ESA said.
What's next? — Studying the mechanism that initiates thunderstorms is tricky. Observing these optical emissions from the Earth's surface does not provide the whole picture, and flying through the clouds during a storm is not a good option either.
However, observing thunderstorms from space gives scientists a rare glimpse of how lightning is initiated in clouds, which may affect the concentration of greenhouse gases in Earth's atmosphere.
Studies have shown that global warming would increase the amount of lightning by 10 percent for every warmer degree. Each lightning strike would also trigger a chemical reaction that produces nitrogen oxide, a greenhouse gas.
Climate change, in turn, increases the severity of thunderstorms. As the crisis continues, observations from above may give scientists better clues for what we're headed toward.
Abstract: Blue jets are lightning-like, atmospheric electric discharges of several hundred millisecond duration that fan into cones as they propagate from the top of thunderclouds into the stratosphere1. They are thought to initiate in an electric breakdown between the positively charged upper region of a cloud and a layer of negative charge at the cloud boundary and in the air above. The breakdown forms a leader that transitions into streamers2 when propagating upwards3. However, the properties of the leader, and the altitude to which it extends above the clouds, are not well characterized4. Blue millisecond flashes in cloud tops5,6 have previously been associated with narrow bipolar events7,8, which are 10- to 30-microsecond pulses in wideband electric field records, accompanied by bursts of intense radiation at 3 to 300 megahertz from discharges with short (inferred) channel lengths (less than one kilometre)9,10,11. Here we report spectral measurements from the International Space Station, which offers an unimpeded view of thunderclouds, with 10-microsecond temporal resolution. We observe five intense, approximately 10-microsecond blue flashes from a thunderstorm cell. One flash initiates a pulsating blue jet to the stratopause (the interface between the stratosphere and the ionosphere). The observed flashes were accompanied by ‘elves’12 in the ionosphere. Emissions from lightning leaders in the red spectral band are faint and localized, suggesting that the flashes and the jet are streamer ionization waves, and that the leader elements at their origin are short and localized. We propose that the microsecond flashes are the optical equivalent of negative narrow bipolar events observed in radio waves. These are known to initiate lightning within the cloud and to the ground, and blue lightning into the stratosphere, as reported here.
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