Outer space weather forecast for Earth contains plenty of solar wind

December 12, 2011

Every day, a newspaper, the television or the Internet offers predictions on precipitation and temperature conditions in your home town. Weather hounds might read forecasts for the opposite side of the country or even the planet. But we earthlings have a very egocentric view of the weather. There are weather events occurring just outside our atmosphere, hovering over our neighboring planets and even developing on the surface of the sun. You won’t find that in your five-day forecast. Yet distant weather can have a serious impact on humankind.

The weather forecast for outer space wouldn’t look much like your local forecast. Space meteorologists don’t track the jet stream, rain or temperature. They’re more concerned with magnetic fields, radiation and high-energy particles.

Winds, however, are as much a part of space weather as they are of terrestrial weather. The solar winds, to be precise. It all starts in the corona, a band of particles that starts near the sun’s surface and extends outward for more than 600,000 miles. You can see the corona as the glow around the moon when it eclipses the sun.

The corona is composed of charged particles heated to more than a million degrees Celsius. At that temperature, the particles are moving so fast that even the immense gravitational pull of the sun cannot hold them. The hot, charged particles surge away from the sun in all directions, creating solar winds that travel 900,000 to 1.8 million miles per hour. Some of those particles head straight toward Earth.

The solar wind is always blowing our way, but the volume and speed of the particles change with weather events on the sun’s surface. Solar weather depends not on pressure and gravity, as on Earth, but on magnetic fields. In areas of intense magnetic activity, the fields sometimes become twisted, cross or snap. When that happens, an incredible amount of energy is released in a process called “magnetic reconnection.” The effect can be a billion times stronger than the bomb the United States dropped on Hiroshima.


Solar weather experts, or heliophysicists, refer to the expulsion of large amounts of particles from the sun as a coronal mass ejection. They can involve as much as 220 billion pounds of charged material. While these incidents aren’t going to blow up Earth or even noticeably alter the Washington region’s weather on a given day, they can be a very serious problem.

“Solar weather events have been occurring for millions of years, but they didn’t directly affect humans until recently,” says Madhulika Guhathakurta. She’s the head scientist for NASA’s Living With a Star project, which is helping astrophysicists better understand solar weather. “Hundreds of years ago, technology was too primitive to be disturbed by space weather. Today, we rely on countless devices that are vulnerable to a solar storm.”

Think of all of the material you use that requires an electrical current: computers, televisions, cellphones, etc. Every one of those things is susceptible to a massive blast of ions from the sun.

Planes flying over the poles are vulnerable to coronal mass ejections. Satellites can go haywire, and even collide, as a result of solar weather events. And astronauts on the international space station are cautioned to stay inside during solar incidents to avoid a massive blast of radiation.

Fortunately, we live under a sort of umbrella called the magnetosphere. It’s a region of intense magnetic activity that surrounds Earth, deflects the solar wind and sweeps its charged particles away into outer space. On the side of Earth not facing the sun, the magnetosphere extends more than 300,000 miles or so. But the solar winds are so powerful that, on the bright side of Earth, they compress the magnetosphere to just 45,000 miles or so. And, at times, the magnetosphere fails us.

“Sometimes, magnetic structures in the solar wind line up in just the right way to cancel out Earth’s magnetic field,” says Guhathakurta. “When this happens, our planetary shielding is weakened. Solar wind pours in and fuels strong geomagnetic storms.”

You might not realize it, but the solar wind has compromised our technology. Power grids are particularly susceptible. In 1989, a relatively small coronal mass ejection damaged transformers in North America and Great Britain. A solar storm caused a blackout in Sweden in 2003.

Guhathakurta’s team and NASA’s Heliophysics division provides data concerning solar events and particle data from NASA spacecraft to the National Oceanic and Atmospheric Administration, the nation’s official space weather forecasting service. It has to assess the risks and issue alerts to air traffic control, or recommend that utilities power down parts of the grid to protect against a major failure. At times, the agency has just 30 minutes to decide whether to issue a warning, because it’s impossible to know whether the magnetosphere is aligned so as to let the particles through until they get close to Earth.

Such incidents are likely to be frequent in the years ahead. The sun’s magnetic activity runs on 11-year cycles, and NASA believes that 2011 and 2012 represent the peak of the cycle. So, the next time your cellphone drops a call, maybe you’ll have to blame the sun rather than your carrier.

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