11:32 am - Monday May 28, 2012

Solar Flares

solar-flareA solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy (about a sixth of the total energy output of the Sun each second). The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day or two after the event. The term is also used to refer to similar phenomena in other stars, where the term stellar flare applies.

Solar flares affect all layers of the solar atmosphere (photosphere, chromosphere, and corona), when the medium plasma is heated to tens of millions of kelvins and electrons, protons, and heavier ions are accelerated to near the speed of light. They produce radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays, although most of the energy goes to frequencies outside the visual range and for this reason the majority of the flares are not visible to the naked eye and must be observed with special instruments. Flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. The same energy releases may produce coronal mass ejections (CME), although the relation between CMEs and flares is still not well established.

Causes of Solar Flares

Flares occur when accelerated charged particles, mainly electrons, interact with the plasma medium. Scientific research has shown that the phenomenon of magnetic reconnection is responsible for the acceleration of the charged particles. On the Sun, magnetic reconnection may happen on solar arcades – a series of closely occurring loops of magnetic lines of force. These lines of force quickly reconnect into a low arcade of loops leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy in this reconnection is in the origin of the particle acceleration. The unconnected magnetic helical field and the material that it contains may violently expand outwards forming a coronal mass ejection. This also explains why solar flares typically erupt from what are known as the active regions on the Sun where magnetic fields are much stronger on an average.

Effects of Solar Flares

The impact of a series of eruptions on the sun began arriving at Earth on Friday and could affect some communications for a day or so.

Operators of electrical grids are working to avoid outages, but the National Oceanic and Atmospheric Administration says some satellite communications and Global Positioning Systems could face problems.

Three solar flares erupted on the sun starting Tuesday, and the strongest electromagnetic shocks were being felt Friday by the ACE spacecraft, a satellite that measures radiation bursts a few minutes before they strike Earth, said Joseph Kunches, a scientist at NOAA’s Space Weather Prediction Center in Boulder, Colo.

Tom Bogdan, director of the center, said the sun is going from a quiet period into a busier cycle for solar flares and an increase in the number of such blasts is expected over the next three to five years.

Solar flares send out bursts of electromagnetic energy that strike the Earth’s magnetic field. The most common impacts for the average person are the glowing auroras around the north and south poles, and the researchers said those could be visible this weekend.

Solar flares strongly influence the local space weather in the vicinity of the Earth. They can produce streams of highly energetic particles in the solar wind, known as a solar proton event, or “coronal mass ejection” (CME). These particles can impact the Earth’s magnetosphere (see main article at geomagnetic storm), and present radiation hazards to spacecraft, astronauts and cosmonauts.

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