solar flare - Solar-B Spacecraft, Classification of flares, Hazards

A violent release of energy in the vicinity of an active region on the Sun, emitting energetic particles, X-rays, and radio waves. It causes notable auroral displays in our upper atmosphere.

Solar flares take place in the solar corona and chromosphere, heating plasma to tens of millions of kelvins and accelerating the resulting electrons, protons and heavier ions to near the speed of light. The energy efficiency associated with solar flares may take several hours or even days to build up, but most flares take only a matter of minutes to release their energy.

Solar flares were first observed on the Sun in 1859.

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". At the peak of the cycle there are typically more sunspots on the Sun, and hence more solar flares.

Solar-B Spacecraft

A new spacecraft, currently called "Solar-B", was launched by Japan in September of 2006 to observe solar flares in more precise detail. The device is meant to study the powerful magnetic fields that are thought to be the source of solar flares. See

Classification of flares

Solar flares are classified as A, B, C, M or X according to the peak flux (in watts per square meter, W/m W/m2. Within a class there is a linear scale from 1 to 9, so an X2 flare is twice as powerful as an X1 flare, and is four times more powerful than an M5 flare.

Two of the largest GOES flares were the X20 events (2 mW/m). However, the GOES detectors were saturated at the peak of the flare, and it is now thought that the flare was between X40 (4.0 mW/m), based on the influence of the event on the earth's atmosphere (see ). The flare originated in sunspot region 10486, which is shown in the illustration above several days before the flare.

The most powerful flare of the last 500 years is believed to have occurred in September 1859: it was seen by British astronomer Richard Carrington 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).

Hazards

Solar flares and associated Coronal Mass Ejections (CMEs) strongly influence our local space weather.

Solar flares release a cascade of high energy particles known as a proton storm. 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.

The radiation risk posed by solar flares and CMEs is one of the major concerns in discussions of manned missions to Mars or to the moon.