Coronal Ejections and Magnetic Storms

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Coronal Ejections and Magnetic Storms

Coronal mass ejections (CMEs) are explosive and violent eruptions of charged, magnetic field-inducing particles and gas (plasma) from the suns outer coronal layer. The amount of mass ejected from the suns corona in these events can be massive (e.g., estimates of CME mass often range in the billions of tons). Ejections propel particles in specific directions, some directly crossing Earths orbital position, at velocities up to 1, 200 miles per second (1, 931 km per second) in an ionized plasma.

Although a constant flow of ionized plasma, the solar wind, moves outward from the sun in all directions, CMEs cause large-scale increases in wind density and velocity that, if they intercept the Earths orbit, are capable of generating geomagnetic storms. A geomagnetic storm is a disruption of the Earths magnetic field and its ionosphere that affects radio communications and sometimes power transmission lines, but is not related to the occurrence of meteorological storms (hurricanes, thunderstorms, etc.) on the surface. Intense storms may interfere with communications and preclude data transfer from Earth orbiting satellites.

Solar coronal ejections and magnetic storms provide the charged particles that result in the northern and southern lightsaurora borealis and aurora australialiselectromagnetic phenomena that usually occur near Earths polar regions. The auroras result from the interaction of Earths magnetic field with ionic gas particles, protons, and electrons streaming outward in the solar wind.

The rate of solar coronal ejections is correlated to solar sunspot activity that cycles between maximum levels of activity (i.e., the solar maximum) approximately every 11 years. During solar maximums, it is not uncommon to observe multiple coronal ejections per day. At solar minimum, one solar coronal ejection per day is normal. The last peak of activity occurred in 2001.

Earths iron core provides it with a relatively strong global magnetic field (oriented about 1012 degrees off the axis of global rotation). Earths magnetosphere protects the Earth from bombardment by deflecting and modifying the solar wind. At the interface of Earths magnetosphere and the solar wind, there is a bow wave or magnetic shock wave that forms a magnetosheath protecting the underlying magnetosphere that extends into Earths ionosphere.

Coronal mass ejections not only interact with Earths magnetic field, they also interact with each other. Stronger or faster ejections may subsume prior weaker ejections directed at the same region of space in a process known as CME cannibalization. Accordingly, the strength of magnetic storms on Earth may not directly correlate to observed coronal ejections. In addition, CME cannibalization can alter predicted arrival time of geomagnetic storms because the interacting CMEs can change the eruption velocity.

See also Atmospheric optical phenomena; Atomic theory; Bohr model; Element, chemical; Solar activity cycle; Solar flare; Solar prominence; Stellar evolution; Stellar magnetic fields; Stellar wind.

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