Life on earth is crucially dependent on a steady output of thermal radiation from the sun. It is indeed fortunate that the sun’s radiation luminosity remains very steady, not varying more than one-tenth of a percent, i.e. by one part in thousand.

Even a one per cent variation would be disastrous. Many sun-like stars do not have such a steady output.  However the sun’s surface is by no means calm. It is seething with activity with groups of sunspots with large localised magnetic fields dissipating their energy at any given time, leading to a lot of turbulent motion of gases. In other words the solar surface is very ‘stormy’! Like we have tornadoes, lightning discharges, etc in our own turbulent atmosphere, every now and then we have giant magnetic explosions on the sun called solar flares!

On an eleven-year cycle, this stormy activity rises and falls. We are now in cycle 24. Cycle 23 produced more than 20,000 flares (from 1996-2007). In addition, the cycle resulted in more than 13,000 coronal mass ejections (CMEs) which releases several billion tons of ionized gas or plasma that hurtles through inter-planetary space at speeds of several million kilometres per hour. These energetic events while producing beautiful auroral displays can severely damage the electronic devices on orbiting satellites and disrupt radio communication and power supplies.

The Halloween storm
For instance, a major flare of November 4, 2003 (called Halloween solar storm as it was triggered on that date) completely crippled instruments on several spacecraft (including the Mars Odyssey) and caused a blackout in Sweden.

The flares can also strongly ionize the atmosphere so that radio communication at some frequencies is halted for hours.  Induced currents can destroy transformers and other equipment affecting national power grids. The 2003 blackout in the north eastern US affected 12 states and Canadian provinces, involving 50 million people costing 6 billion dollar damages over a day! On December 5 and 6, 2006, as solar cycle 23 approached its maximum, two powerful x-ray flares exploded on the sun’s limb.

In August 1972, a very intense solar storm led to large scale blackout putting many satellites out of order. Areas of intense magnetism such as in arching magnetic loops are sources of solar storms. The 2003 Halloween storms were launched by presence of enormous sunspots (of several earth diameters in size) peppering solar active regions.

For the current solar cycle, this year would be near the peak of activity and an initial warning sign of a solar storm or even super-storm could be the presence of a large distorted sunspot group.

There could be dozens of x-ray flares of even moderate intensity (classes as x-10, the most intense being x-20) each flare causing short-wave radio blackouts. For example, a large sunspot group (called active region 9393) found in March 2001, led to a large flare on 2 April 2001. The armada of solar research satellites like Hinode, SDO, STEREO, could be the first to sense such eruptions.

An intense blast of x-rays and energetic protons could blackout every sensor system in space and the x-ray pulse could also destroy the ionized atmospheric D-layer.  On September 1, 1859, the sun produced one of its most spectacular super-storms (largest over 500 years). The first CME arrived on August 28 1859. It spawned aurorae as far south as Greece. The atmosphere lost about 10% of its ozone layer and the night sky blazed bright to confuse animals and people.

In 1859, British astronomers, Richard Carrington and Richard Hodgson, witnessed this rare super-flare, such an event occurring once in a few centuries. They described the flare as a “brilliant star of light, much brighter than the sun’s surface and most dazzling”. It ended after 5 minutes. The 1859 storm had four times the power of the 1972 storm, the largest in recent decades.

Tough to predict
Solar scientists cannot predict when one of these super-storms would occur. Around 1859, when technology was much less developed, only telegraph outages and instrument fire constituted damage (indeed the telegraph offices on both sides of the Atlantic were set on fire). Such an event occurring today with sophisticated electronic technology engulfing our lives every minute could be disastrous. There would also be instant hazard to air travel with days of delay and rerouting.

Accelerated by CME shock waves a tremendous pulse of high energy protons would invade satellite circuitry and cause losses of several thousand of crores of rupees. The GPS system could become inaccurate impacting navigation, military operations, etc. Our technology can only be thankful that these super-flares are statistically rare.

But who knows? The sun may unleash a super-storm with major flares and eruptions this year. This so-called space weather is as unpredictable as our earthly weather, with tsunamis occurring with little warning! So also a solar super-storm!