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Solar-Earth Magnetic Phenomena
The Sun's surface is a huge mass of charged particles called plasma. Plasma is a state of matter in which atoms have been heated to the point that they have lost their electrons and become electrically charged. Magnetic fields, such as those of the Sun and Earth, bend plasma into curls and arc-like shapes. Especially during the active parts of its cycle, the Sun ejects jets of plasma, moving at speeds up to 50,000 miles per second. Some of these are large enough to reach Earth.
Though it thins out as it covers the 93 million miles between Sun and Earth, a very large solar flare still can cause strong effects. A strong plasma jet can flatten the day-side half of the Earth̵7;s magnetic field while stretching the night side. It follows the field toward the north and south poles, producing colorful auroral displays in the sky. Some components of a solar flare interact with the upper layers of Earth's atmosphere, affecting radio waves.
Ionosphere and Radio Broadcasting
About 60 miles above sea level lies the ionosphere, an atmospheric layer of very low pressure, about 100 miles thick. The ionosphere gets its name from the ions that cosmic radiation produces where the atmosphere transitions into the vacuum of space. Because of the ionosphere̵7;s electrically charged nature, it reflects radio waves having frequencies below 30 MHz, such as AM and shortwave radio signals. FM radio frequencies are above 80 MHz and pass through the ionosphere. Because AM and shortwave radio signals are reflected back to Earth by the ionosphere, a person with a receiver can hear broadcasts hundreds to thousands of miles away.
Solar flares generate more ions in the ionosphere. The energy and particles in a solar flare churn the ionosphere, making it thinner in some places and thicker in others. This means some areas receive distant radio broadcasts more clearly, while others receive nothing.
Noise
A certain amount of electrical noise is always present in the ionosphere. A solar flare̵7;s particles increase this noise. A flare's effects can ̶0;drown out̶1; radio broadcasts, making them inaudible. Because the noise occurs at many frequencies, solar flare activity can interfere with a range of radio signals, including those for cell phones, AM and FM radio, and GPS.
Electrical Damage
Because of their location in space, unprotected by the atmosphere, communications satellites are particularly vulnerable to electrical damage by solar flares. Energetic charged particles come into contact with sensitive electronic circuits, burning them out. Particularly strong solar flares also cause problems on Earth. Any long wire, such as a radio antenna or telephone line, picks up the energy from a flare and sends electrical bursts into sensitive circuits, sometimes damaging them.