Space weather and radiation
Space weather events pose a risk to technology, infrastructure, electrical systems and, to a limited extent, public health.
There are numerous types of weather on earth and they all produce different kinds of effects. Space weather covers a broad range of phenomena associated with areas of magnetic turbulence near the surface of the Sun, in particular large clusters of sun spots, coronal mass ejections, solar energetic particle events, solar flares and solar radio bursts; each pose different risks.
For the most part, space weather events pose risks to technology, infrastructure, and electrical systems, though there is the potential for some limited health effects.
Radiation from space penetrates the Earth’s atmosphere all the time; each year about 12% of the radiation dose members of the UK public receive, comes from exposure to cosmic rays. Some of this is from flying in aircraft, where the combined shielding effects of the Earth’s atmosphere and its magnetic field are reduced, but most comes from the radiation that reaches ground level. The doses people receive on the ground are tiny, but air crew are routinely assessed for their radiation exposure because the dose rates are higher at altitude.
A significant space weather event may cause people on the ground to receive an unusual radiation dose, though it would be far too small to produce an observable health effect. Those flying in planes during a space weather event would be likely to receive a higher radiation dose – but again it is extremely unlikely to produce adverse health effects for individuals who are exposed. The radiation doses people receive will be dependent on where they are on the planet, how big an event it is, how long it lasts and other factors, altitude and proximity to the magnetic poles being key factors. This may only be able to be determined after the event.
What space weather is
Space weather is driven primarily by what happens on the surface of the Sun, which can subject the Earth to energetic particles and magnetic fields. Storms on the surface of the Sun are seen as sun spots or clusters of sun spots, which are regions where the Sun’s surface is subject to severe magnetic turbulence. These can result in the ejection of high energy radiation in a solar flare which is sometimes accompanied by a coronal mass ejection (CME), a large quantity of solar plasma contained within magnetic turbulence.
The solar flare consists of high energy x-rays, charged particles and UV radiation that reach the Earth at or near the velocity of light, ie within a few minutes. Particles called protons are potentially harmful to people because they generate neutrons and muons in the upper atmosphere that can easily reach aircraft cruising altitudes and to a lesser extent reach ground level. Generally, the Earth’s magnetic field protects us from the damaging effects of these particles, which are seen as the aurora, or northern and southern lights, near the magnetic poles.
A CME reaches the Earth more slowly, typically taking 2 or 3 days. Its effects can impact on technology and infrastructure. The magnetic field associated with the CME can over-ride the Earth’s magnetic field, making it easier for radiation to reach the upper atmosphere; this is seen as particularly bright aurora extending to lower latitudes than is normal. The accompanying magnetic fields can also induce strong currents in conductors that can disrupt the electricity grid and satellite systems. There may be a ‘bow wave’ of energetic protons accelerated by the CME that causes higher than normal radiation dose rates at aviation altitudes.
In 1989 a space storm had disrupted electricity networks in Quebec in Canada, which led to a 9 hour power cut across the province. In other episodes telegraph systems, radio systems and satellites have been interrupted by space weather events and the UK government considers that because modern life relies on so much technology which could be hampered by a space weather event, plans should be drafted to cope with a major incident. The loss of satellite communications could result in temporary loss of Global Positioning System (GPS) signal and could affect some other communication systems.
The Sun has an 11 year solar cycle between peaks of activity. Sun spot activity has been recorded by solar observers for more than a thousand years, but the 11 year periodicity was only noticed in the 19th century while it varies in strength, the approximate 11 year gaps between ‘solar maxima’ are fairly regular. These are characterized by increased sun spot activity and greater frequency of solar flares. Recent solar maxima have centred around 1981, 1992 and 2003, so 2013 to 2014 is also a period of solar maximum. Periods between maxima are much quieter and are termed ‘solar minima’. There is currently much discussion about the degree of linkage between extreme solar storms and stage of the solar cycle.
It is possible that a solar storm could produce higher than usual radiation dose rates. Increased doses are sometimes measureable at sea level, as the so-called ground level events (GLE). Such events are not uncommon, but when an elevated dose rate is measured at ground level the increase at aircraft altitude is more marked. Since 1942, when records began, there has averaged about 1 GLE per year, but they are most frequent around solar maximum. However, only a few of these would have produced significantly increased dose rates for air crew and passengers and none would have significantly altered individual’s lifetime risk of cancer.
There have been few major space weather events since technology was created that could be affected by them, or methods were available to measure their effects. Best estimates, based on the kind of event that scientists think might happen once every 200 years, show that radiation doses to people on the ground would be small and roughly the same size dose as holidaying in Cornwall for a week, where background radiation is higher because of levels of naturally occurring radioactive gas radon. Even those flying during a major storm would only receive an additional radiation dose equivalent to spending 2 to 3 years in Cornwall.
Major events are very rare and even these unusual dose levels will not alter the lifetime risk from radiation for individuals by a measureable amount.
The Health Protection Agency, now Public Health England (PHE), contributed to an assessment of the potential risks with the Royal Academy of Engineering.
PHE is considering if further work is required on radiation impacts.