Mystery behind why satellites lose GPS connection solved

'Thunderstorms' in the ionosphere are to blame for the black out of the Global Positioning System (GPS) systems on low-orbiting satellites when they fly over the equator between Africa and South America, a new study has found.
European Space Agency's (ESA) Swarm, a trio of satellites, is measuring and untangling the different magnetic fields that stem from Earth's core, mantle, crust, oceans, ionosphere and magnetosphere.
The Swarm satellites carry GPS receivers as part of their positioning system so that operators keep them in the correct orbits. In addition, GPS pinpoints where the satellites are making their scientific measurements.
However, sometimes the satellites lose their GPS connection. In fact, during their first two years in orbit, the link was broken 166 times.

The new study shows that there is a direct link between these blackouts and ionospheric 'thunderstorms', around 300-600 km above Earth.
"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 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," said Stolle.
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.

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 so that the Swarm GPS receivers can lose track.
As many as 161 of the 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'.
Resolving the mystery of blackouts is not only good news for Swarm, but also for other low-orbiting satellites experiencing the same problem.

"What we see here is a striking example of a technical challenge being turned into exciting science, a true essence of an Earth Explorer mission such as Swarm," said Rune Floberghagen, ESA's Swarm mission manager.
"These new findings demonstrate that GPS can be used as a tool for understanding dynamics in the ionosphere related to solar activity. Perhaps one day we will also be able to link these ionospheric thunderstorms with the lightning we see from the ground," said Floberghagen.