Thunderstorms revealed to disrupt satellite tracking
‘Thunderstorms’ in the ionosphere may be the cause of satellite blackouts when they fly over the equator between Africa and South America, new research shows.
Low orbiting satellites such as ESA Swarm, which is currently measuring and untangling magnetic fields around the Earth, sometimes lose the GPS connection that keeps them in the correct orbit. Since its launch in 2013, Swarm has experienced a broken link 166 times.
However, a recently published paper describes how Swarm has revealed there is a direct link between these blackouts and ionospheric thunderstorms, around 300–600 km above Earth.
These thunderstorms occur when the number of electrons in the ionosphere undergoes large and rapid changes. This tends to happen close to Earth’s magnetic equator and typically just for a couple of hours between sunset and midnight.
“Ionospheric thunderstorms are well known, but now we have been able to show a direct link between these storms and the loss of connection to GPS,” said Claudia Stolle from the GFZ research centre in Potsdam, Germany.
“This is thanks to Swarm, because it is the first time that high-resolution GPS and ionospheric patterns can be detected from the same satellite.”
The ionosphere is where atoms are broken up by sunlight, which leads to free electrons. A thunderstorm scatters these free electrons, creating small bubbles with little or no ionised material. These bubbles disturb the GPS signals, causing the Swarm GPS receivers to lose track.
It transpires that 161 of the recorded lost signal events coincided with ionospheric thunderstorms. The other five were over the polar regions and corresponded to increased strong solar winds that cause Earth’s protective magnetosphere to ‘wobble’.
“In light of this new knowledge, we have been able to tune the Swarm GPS receivers so they are more robust, resulting in fewer blackouts,” said Christian Siemes, who works at ESA on the mission.
“Importantly, we are able to measure variations in the GPS signal, which is not only interesting for engineers developing GPS instruments, but also interesting to advance our scientific understanding of upper-atmosphere dynamics.”
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