Forbush Decrease

The primary sources of solar cosmic rays are solar flares and coronal mass ejections which eject large quantities of material from the Sun at speeds of between 400 – 1,000 km/s. When such a large magnetic disturbance arrives at Earth, it sweeps away some of the incoming galactic cosmic rays resulting in a decrease in their rate of detection. This decrease, and the correlation with the increase in solar cosmic rays, was discovered by Scott Forbush and is now known as the Forbush decrease.

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