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Solar flare? Maybe not. Explaining four different kinds of solar storms.
The News - Science-Astronomy
August 16, 2013
solar flare types
Earthlings first took note of the sun's impact on technology in 1859, when a high-energy outburst disrupted telegraph service and lit the night sky with auroras as far south as Hawaii and Cuba. That event remains the strongest geomagnetic storm to date since the dawn of the Industrial Age, scientists say.

Like terrestrial storms, these events trigger effects that range from beautiful to annoying to dangerous. But what causes them? Here we explain four different kinds of solar outbursts – such as solar flares – that can impact us here on Earth.

This Solar Dynamics Observatory image in extreme ultraviolet light shows a dark coronal hole near the center of the sun's disk. (AIA/SDO/NASA/File)

1. Coronal holes

These are weak spots in the magnetic field of the sun's corona that allow protons and electrons to leave the star a speeds of around 1.7 million miles an hour. This release is known as fast solar wind, in contrast to the slow solar wind, which constantly streams from the sun at 900,000 miles an hour from along the sun's equatorial regions. During the low point in the 11-year sunspot cycle, these holes usually are found near the sun's poles. But during the peak of the cycle they can crop up almost anywhere on the sun. They tend to appear near the sun's equator as sunspot activities declines during a sunspot cycle. Holes appearing at this location trigger the strongest effects on Earth's space weather. The fast solar wind can trigger mild disruptions in Earth's magnetic field, which can induce relatively small voltage spikes on long-distance power-transmission lines and disrupt radio communications in polar regions. In addition, these fast particles leaking through the coronal hole can brighten up the auroras.

2. Solar filaments

Seen from overhead, filaments appear as dark, thread-like features across the sun's surface. They consist of searingly hot gas that nevertheless is cooler than the surface. Seen broadside, however, they form a visible arch above the sun's surface, known as a solar prominence. The arc traces a looping magnetic field the electrically charged gas follows. Filaments are thought to be one source for coronal-mass ejections, vast, high-speed clouds of charged particles that filaments can release in crack-the-whip-like fashion if one end of the magnetic loop looses its grip. The coronal-mass ejections from filaments tend to be relatively weak.


A photo from the National Solar Observatory of a 2006 solar flare. (National Solar Observatory/AP/File)

3. Solar flares

Flares emit radiation at wavelengths ranging from radio frequencies at the low end to gamma rays at the high end. Most of the radiation, however appears at wavelengths above visible light. Flares, which are associated with sunspots, are driven by energy released when magnetic fields rising from deep in the sun break and reconnect, releasing large amounts of energy. When extreme ultraviolet and x-ray radiation from the flares reach Earth, they disrupt the ionosphere over low latitudes on the sunlit half of the planet. This can disrupt low- and high-frequency radio communications, such as shortwave broadcast services. Outside of Earth's magnetic field, the incoming high-energy protons form what scientists call a radiation storm, which can disrupt or disable satellites and threated astronauts conducting spacewalks. Because the x-rays and the far-UV light travel at the speed of light, the communications disruptions appear in advance of any geomagnetic or radiation storm the arriving charged particles trigger. Sometimes not by much. In 2005, physicists were stunned by an intense radiation storm from a solar flare; the protons reached Earth in 15 minutes instead of taking a day or more. Light takes 8 minutes to arrive from the sun. Space-weather forecasters pay special attention to strong flares, in no small part because they accompany fast coronal-mass ejections.


An image from the Solar Dynamics Observatory shows a coronal-mass ejection from 2011. REUTERS/NASA//Handout (SDO/NASA/REUTERS/File)

4. Coronal mass ejection

Coronal-mass ejections are associated with flares and filaments. CMEs pack the most powerful punch a solar storm can deliver. The largest of these can send more than 1 billion tons of protons and electrons racing from the sun at speeds of more than 4 million miles an hour. The intensity of the effect they have on Earth depends on the location of the source region on the sun as well as on how strongly the cloud's magnetic field couples to that of Earth as it arrives. The stronger the coupling, the more intense the geomagnetic storm. As the CME travels, it plows through the sun's slower-moving solar wind, creating a shock wave that can turbocharge protons, generating a radiation storm. When it reaches Earth, a CME can trigger an initial, intense geomagnetic storm, followed by a few days of continued disturbance of varying intensity. Effects range from brighter auroras and surges along power grids and long-distance pipelines to intense radiation storms and severely disrupted radio communications in polar regions. During CMEs, airlines reroute fights that ordinarily use polar routes to maintain radio communications for transcontinental flights.

 

 
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