HUGE solar eruptions fired bursts of charged particles at us on two successive days last week. The first outburst, on 28 October, was the largest aimed at the Earth in 30 years, knocking out two Japanese satellites and affecting telecommunications and power grids across the globe.
But it seems we were lucky this time 鈥� the impact of the flares would have been much worse if their magnetic fields had been aligned differently, according to researchers. However, the storm was perfectly timed to rally support for the US space weather center, which is endangered by budget cuts.
Both flares came from the same massive group of sunspots, which is rotating around the surface of the sun. The first occurred at 1154 GMT on 28 October, as the group neared the middle of the sun鈥檚 face. The second came at 2037 GMT the following day, after the spots had crossed the mid line. Respectively, they were the third and 15th most intense flares recorded since 1976, according to John Kohl of the Harvard-Smithsonian Center for Astrophysics. And until last week two such intense flares had never been recorded so close together. 鈥淚鈥檝e not seen anything like it in my entire career as a solar physicist,鈥� says Kohl. Three smaller flares followed early this week, although none were aimed directly at Earth.
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Solar flares are explosions that happen at sunspots and convert magnetic energy into kinetic energy. The resulting visible light, X-rays and gamma rays reach Earth in minutes. An intense burst of charged particles follows, travelling at up to 1500 kilometres per second. It鈥檚 the particles that produce a geomagnetic storm, typically a day or more after the flare, when they hit the Earth鈥檚 magnetic field. The first intense flare last week hit us 17 hours after leaving the sun, triggering a geomagnetic storm that the US National Oceanic and Atmospheric Administration鈥檚 Space Environment Center (SEC) rated as 鈥渆xtreme鈥�, the highest possible category.
But according Bruce Tsurutani of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California, the effects still didn鈥檛 come close to the most intense storm on record, which on 1 and 2 September 1859 melted telegraph wires. Then the intensity of the Earth鈥檚 magnetic field fluctuated by 1720 nanotesla near the equator, nearly triple the 640 nanotesla recorded during a 1989 storm that knocked out the Quebec power grid. By comparison this week鈥檚 storm caused fluctuations up to only 347 nanotesla.
Tsurutani told New Scientist that four factors are necessary for a 鈥減erfect storm鈥� like the one in 1859 鈥� the outburst must be moving fast, it must hit the Earth, it must be very intense, and its magnetic field must be aligned exactly opposite to the Earth鈥檚. Last week鈥檚 outbursts met the first three requirements, but their magnetic fields were not aligned, so their impact was minimal.
A magnetic storm can induce strong currents in power grids, build up charge on satellites, and disrupt radio communications. This time, forewarned of the storm, operators shut down satellites and reduced voltage levels on power grids so that magnetic fluctuations induced by the storm did not exceed safe levels. Airlines rerouted flights crossing polar regions, where communications are most seriously disrupted.
In the future, we may not have such good warning of storms as the SEC faces imminent closure. The US House of Representatives wants to cut the centre鈥檚 funding a little, but the Senate has voted to slash it to zero. The two committees often split the difference when they disagree, but no decision has yet been made, and an interim resolution that kept funding at last year鈥檚 level expires this week.
Last week, representatives of NASA, United Airlines, the US air force and satellite operator Loral Skynet all urged that the SEC鈥檚 funds be restored. 鈥淟osing the SEC forecast that supports space missions would be like living along a coastal area without any hurricane forecasting capability,鈥� says John Grunsfield, chief scientist at NASA. 鈥淵ou would know when the hurricane hit you, but you would have no advanced warning, no ability to take preventative actions, and no idea how strong it would be or how long it would last.鈥�