Penetrating Earths Magnetic Defense

Particles in the solar wind transport only one ten-billionth the energy of that carried by sunlight, and Earth is protected from the full blast of the dilute, varying solar wind by the terrestrial magnetosphere. tte Earth's magnetic shield is so perfect that only 0.1 percent of the mass of the solar wind that hits it manages to penetrate inside. Yet, even that small fraction of the wind particles has a profound influence on the Earth's environment in space, ttey create an invisible world of energetic particles and electric currents that flow, swirl and encircle the Earth, suspended high above its atmosphere.

As the solar wind brushes past the Earth, the wind carries some of the Sun's magnetic field with it. And since magnetic fields have a direction, the solar wind's magnetism can point toward or away from the direction of the Earth's magnetic field. If the solar field points opposite to that of the Earth when they meet, the two can join each other, just as the opposite poles of two toy magnets stick together, tte magnetic field in the solar wind is then broken, and reconnects with the terrestrial magnetic field, plugging the solar wind into the Earth's electrical socket and wiring its magnetosphere to the Sun. Ms magnetic coupling occurs on the dayside facing the Sun and is dragged downstream all along the length of the Earth's magnetotail. And since the immense magnetic tail forms the bulk of the magnetosphere, it provides the main location for breaching the Earth's magnetic defense.

tte passing solar wind is slowed down by the connected fields and decelerates in the vicinity of the tail. Energy is thereby extracted from the nearby solar wind and drives a large-scale circulation, or convection, of charged particles within the magnetosphere (Fig. 8.4). While creating and sustaining the magnetotail, the solar wind brings the oppositely directed tail lobes into close contact, where they can merge together, tte magnetotail then snaps like a rubber band that has been stretched too far. tte

FIG. 8.4 Magnetic connection on the back side The Sun's wind brings solar and terrestrial magnetic fields together on the night side of Earth's magnetosphere, in its magnetotail. Magnetic fields that point in opposite directions (thin arrows), or roughly toward and away from the Earth, are brought together and merge, reconnecting and pinching off the magnetotail close to Earth. Material in the plasma sheet is accelerated away from this disturbance (thick arrows). Some of the plasma is ejected down the magnetotail and away from the Earth, while other charged particles follow magnetic field lines back toward Earth.

Solar Wind

Solar Wind

FIG. 8.4 Magnetic connection on the back side The Sun's wind brings solar and terrestrial magnetic fields together on the night side of Earth's magnetosphere, in its magnetotail. Magnetic fields that point in opposite directions (thin arrows), or roughly toward and away from the Earth, are brought together and merge, reconnecting and pinching off the magnetotail close to Earth. Material in the plasma sheet is accelerated away from this disturbance (thick arrows). Some of the plasma is ejected down the magnetotail and away from the Earth, while other charged particles follow magnetic field lines back toward Earth.

snap catapults part of the tail downstream into space, creating a gust-like eddy in the solar wind.

tte other part of the tail, propelled by energy released in the magnetic merging, rebounds back toward our planet. Electrons and ions hurtle along magnetic conduits that are connected to the Earth, linking the solar wind to both equatorial storage regions and down into the polar caps, tte electrons that are guided into the poles augment and intensify the northern and southern lights, or auroras. And the tail continues to reform into another, potentially explosive, unstable configuration to await the next magnetic connection.

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