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Solar flares

astrofísica,espacio,research — Tags: , , , — alejandro @ November 1, 2010

“Solar flares are the most powerful explosions in the solar system. Packing a punch equal to a hundred million hydrogen bombs, they obliterate everything in their immediate vicinity. Not a single atom should remain intact.” [1]

“They happen every few days or weeks. The Aug. 24th event was powerful, yet typical.”

“Magnetism and solar flares go together. On the sun, flares happen when magnetic fields above sunspots become twisted and stretched. They’re like rubber bands pulled too tightly. Snap! They recoil with explosive results. Physicists call this “magnetic reconnection.”" [2]

Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to x-rays and gamma rays at the short wavelength end. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time! This energy is ten million times greater than the energy released from a volcanic explosion.

There are typically three stages to a solar flare. First is the precursor stage, where the release of magnetic energy is triggered. Soft x-ray emission is detected in this stage. In the second or impulsive stage, protons and electrons are accelerated to energies exceeding 1 MeV. During the impulsive stage, radio waves, hard x-rays, and gamma rays are emitted. The gradual build up and decay of soft x-rays can be detected in the third, decay stage. The duration of these stages can be as short as a few seconds or as long as an hour.

The frequency of flares coincides with the Sun’s eleven year cycle. When the solar cycle is at a minimum, active regions are small and rare and few solar flares are detected. These increase in number as the Sun approaches the maximum part of its cycle. The Sun will reach its next maximum in the year 2011, give or take one year.

The radio and optical emissions from flares can be observed with telescopes on the Earth. Energetic emissions such as x-rays and gamma rays require telescopes located in space, since these emissions do not penetrate the Earth’s atmosphere.

[3]

A solar flare is a large explosion in the Sun’s atmosphere that can release as much as 6 × 1025 joules of energy(about a sixth of the total energy output of the Sun each second).

Solar flares affect all layers of the solar atmosphere (photosphere, corona, and chromosphere), heating plasma to tens of millions of kelvins and accelerating electrons, protons, and heavier ions to near the speed of light. They produce radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays. Most 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. If a solar flare is exceptionally powerful, it can cause coronal mass ejections.

X-rays and UV radiation emitted by solar flares can affect Earth’s ionosphere and disrupt long-range radio communications. Direct radio emission at decimetric wavelengths may disturb operation of radars and other devices operating at these frequencies.

Solar flares were first observed on the Sun by Richard Christopher Carrington and independently by Richard Hodgson in 1859 as localized visible brightenings of small areas within a sunspot group.

The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly “active” to less than one each week when the Sun is “quiet”.

Solar activity varies with an 11-year cycle (the solar cycle). At the peak of the cycle there are typically more sunspots on the Sun, and hence more solar flares.

Solar flares strongly influence the local space weather of the Earth. They produce streams of highly energetic particles in the solar wind and the Earth’s magnetosphere that can present radiation hazards to spacecraft and astronauts.

Energetic particles in the magnetosphere contribute to the aurora borealis and aurora australis.

Solar flares release a cascade of high energy particles known as a proton storm. Energetic protons can pass through the human body, doing biochemical damage. Most proton storms take two or more hours from the time of visual detection to reach Earth’s orbit. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured, taking only 15 minutes after observation to reach Earth, indicating a velocity of approximately one-third light speed.

The most powerful flare of the last 500 years was the first flare to be observed, and occurred in September 1859: it was reported by British astronomer Richard Carrington (it is known as The Carrington Flare) and left a trace in Greenland ice in the form of nitrates and beryllium-10, which allow its strength to be measured today (New Scientist, 2005). The flare was visible to the naked-eye and produced stunning auroras down to tropical latitudes such as Cuba or Hawaii, setting telegraph systems on fire.

In modern times, the largest solar flare measured with instruments occurred in November 4, 2003 (initially measured at X28 and later upgraded to X45). Other large solar flares also occurred in April 2, 2001 (X20), October 28, 2003 (X17) and September 7, 2005 (X17). In 1989, during former solar cycle 22 two large flares occurred in March, 6 (X15) and August, 16 (X20) causing disruptions in electric grids and computer systems. A complete list is available at

http://www.spaceweather.com/solarflares/topflares.html [4]

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[1] http://science.nasa.gov/science-news/science-at-nasa/2008/15dec_solarflaresurprise/

[2] http://science.nasa.gov/science-news/science-at-nasa/2003/12sep_magnetars/

[3] http://hesperia.gsfc.nasa.gov/sftheory/flare.htm

[4] http://en.wikipedia.org/wiki/Solar_flare

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