'Thunderstorms' in the ionosphere are to blame for loss of GPS signals on low-orbiting satellites, says a study that used data from the European Space Agencyâ€™s Swarm mission.
"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," Floberghagen noted.
Launched in 2013, ESA's three Swarm satellites are measuring and untangling the different magnetic fields that stem from Earth's core, mantle, crust, oceans, ionosphere and magnetosphere - an undertaking of at least four years.
As with many satellites, the Swarm trio carries 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 paper, published in Space Weather, a journal of the American Geophysical Union, described how Swarm had revealed 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," one of the study authors Claudia Stolle from GFZ German Research Centre for Geosciences, Potsdam, noted.
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.
As its name suggests, 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, the study said.