Elizabeth Norton, of Hampden, asks :-

Recently there has been news that a solar flare crossed the orbit of the Earth in recent times, missing the Earth by just 5 days. I understand that should a flare such as this strike the Earth, electricity supply, electronic appliances, and communications would be in jeopardy. What would be the most likely consequence of such an event and what could happen in a ‘worst case’ scenario?

Ian Whittaker, a physicist at the University of Otago, responded.

To answer this excellent question we first have to look at the processes on the Sun. Solar flares are a sudden release of energy made up of visible light, X-rays, radio waves and everything in between. These flares, while interesting from a research perspective, have very little effect on the Earth.

Solar flares are usually linked to a phenomenon we call Coronal Mass Ejection's (CME). These are bubbles of solar material (hydrogen and helium particles) that get trapped inside a magnetic field just above the surface of the Sun. It can be imagined like a balloon inflating with the magnetic field acting as the rubber and the solar gas filling it.

The pressure increases and the magnetic field expands until the pressure of the gas is stronger than the magnetic tension. At this point the outer layer of the magnetic field and all the solar material within flies off into space and this is what is dangerous to us.

A solar flare can usually be seen accompanying the CME, but as the flare travels at the speed of light we usually observe it between 1 and 3 days before the arrival of the particles.

The emission of events from the Sun is highly dependent on how 'active' the Sun is. It takes 11 years to go from quiet to active and back to quiet and you can tell the activity by the number of visible sunspots (historically recorded from 1826 although Gallileo also kept track of them, circa 1600).

To answer the first part of your question, we get hit by CME's on a fairly regular basis. What generally happens is that the sea of high energy particles hits our magnetic field and shakes it up. This plays an important role in atmospheric chemistry but the most obvious effect is that the aurora (Northern and Southern lights) can be seen further away from the poles. A CME strike is necessary for aurora to be seen in New Zealand.

A recent report in the scientific journal Space Weather, stated that there was a 12 per cent chance of a dangerously powerful CME hitting the Earth in any ten year period. To put this into context this is approximately one such impact every eighty years.

The first such storm of this kind we are aware of is called the Carrington event in September 1859, in which the preceding solar flare was visible to the naked eye with aurora seen in Cuba!

Since then we have had the incident in 1989 which caused Quebec to be without power for 9 hours. The problem is that the Earth's magnetic field is shaken so much by the CME impact that it generates electrical currents in anything metallic, this means that power lines are especially vulnerable where the extra current can destroy the power station transformers.

The worst case scenario is very serious. Power stations could be damaged over a wide area requiring repairs and replacement parts, likely taking months to recover. In that time the lack of power would stop communications, grinding the financial markets to a halt, stopping emergency services from being contacted and causing services such as water and sewerage to be affected.

Modelling of the situation describes a Carrington strength event to be a 'global Katrina' costing approximately US$30 billion in damages. Such high strength CME-imapcts are relatively rare and now recognised as a threat.

We would get at least a day's warning, preventative measures are in place and research is ongoing into how to protect our electrical networks.