Extreme Space Weather

Extreme Space Weather Events

Start date
1 April, 2014
End date
3 April, 2021

Our modern society is increasingly reliant on satellites for a wide variety of applications including communication, navigation, Earth observation and defence. This growing infrastructure is vulnerable to the damaging effects of space weather.

The concern at government level in the UK is such that severe space weather was added to the UK’s National Risk Register of Civil Emergencies in 2012, where the likelihood of a reasonable worst case scenario occurring in the next year is currently estimated to be between 1 in 20 and 1 in 100.

Artist’s depiction of Sun-Earth interaction (Credit: NASA)

Space weather hazard

Energetic electrons are an important space weather hazard. They affect satellites in two principle ways. Electrons with energies in the range from ∼keV to ∼100 keV, which are injected during substorms, affect the current balance to the satellite surface. This may result in a high level of surface charging. Higher-energy electrons, known “killer” electrons, which tend to build up during geoeffective geomagnetic storms and high speed solar wind streams, can penetrate surface materials and embed themselves within insulators. Such charging is known as internal charging. Both surface charging and internal charging can lead to the build-up of significant amounts of charge, the subsequent discharge of which can damage components.

Electrostatic discharge

“Killer” electrons are found in two regions of near-Earth space – referred to as the inner and outer radiation belts. The inner radiation belt, which typically occurs at altitudes between 650 and 6500 km in the magnetic equatorial plane, is relatively stable. In sharp contrast, the outer radiation belt, which typically occurs at altitudes between 13,000 and 40,000 km, is highly dynamic with fluxes changing by orders of magnitude on timescales ranging from minutes to days. Substorm injected electrons tend to occupy roughly the same region as the outer radiation belt, but in contrast to the “killer” electrons, they are restricted in local time, ranging from the early evening sector through midnight to noon.

Schematic diagram of the Earth’s Van Allen radiation belts (Credit: NOAA)

Risk to satellites

There are currently (as of April 2022) 5465 operational satellites in Earth orbit, of which 4700 are in low Earth orbit (LEO), 565 in geosynchronous orbit (GEO), 140 in medium Earth orbit (MEO), and 60 in elliptical orbit. Most are exposed to energetic electrons for at least some of their orbit. In 2021 the overall global space economy generated revenues of US $386B, showing the importance of the industry to the economy. Extreme space weather events have a real capacity to damage this infrastructure, as happened during a major storm in 2003, when 10% of the satellite fleet experienced anomalies and one satellite (the joint Japanese/US Midori 2 satellite, costing US $640M) was a total loss.

Satellite orbits in the Earth’s Van Allen radiation belts (from Horne et al., 2013)

Mitigating the risks

Our research seeks to determine the conditions that would occur in a 1 in 100 year-event to determine the likely impact of an extreme event. The severity of any given event depends on both location and electron energy.  To understand this, and provide the information that the satellite industry needs, we conduct independent analyses for different electron energies and orbit types. The findings are used by satellite operators and engineers to mitigate the risks to new satellites by improving the definition of spacecraft technical requirements and in the evaluation of satellite proposals received from manufacturers.


Modern satellites in medium Earth orbit and at geosynchronous orbit have life expectancies of 10-20 years. Satellite operators and engineers thus need realistic estimates of the flux levels that may be reached on these and longer timescales in order to assess the likely impact of an extreme event on the satellite fleet and to improve the resilience of future satellites by better design of satellite components. Satellite insurers also require this information to help them in dialogues with clients and in the evaluation of realistic disaster scenarios.

Artist’s depiction of GOES-13 (Credit: NOAA)

Overall Aim

The overall aim of these studies is to determine the 1 in 10, 1 in 50, and 1 in 100 year energetic electron flux levels as a function of energy for various key orbits and locations in near Earth space.


  • The 1 in 100 year event levels can be used as space weather benchmarks as defined by the Space Weather Operations, Research and Mitigation Subcommittee of the National Science and Technology Council
  • The benchmarks can be used to
    • determine the likely impact of an extreme event
    • improve the resilience of future satellites
    • evaluate potential disaster scenarios
  • The benchmarks may also be used for
    • comparison with ongoing events
    • the purposes of situational awareness and operational risk assessments
    • comparison with theoretical maximum fluxes

This work is aligned with the Industrial Strategy challenge for Satellites and Space Technology


Medal win for space weather scientist

13 November, 2020

The award recognises Professor Horne’s unique ability to combine basic and applied research to develop useful space weather products.