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 sun’s outer coronal layer. The amount of mass ejected from the sun’s 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 Earth’s 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 Earth’s orbit, are capable of generating geomagnetic storms. A geomagnetic storm is a disruption of the Earth’s 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 lights—aurora borealis and aurora australialis—electromagnetic phenomena that usually occur near Earth’s polar regions. The auroras result from the interaction of Earth’s 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.

Earth’s iron core provides it with a relatively strong global magnetic field (oriented about 10–12 degrees off the axis of global rotation). Earth’s magnetosphere protects the Earth from bombardment by deflecting and modifying the solar wind. At the interface of Earth’s 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 Earth’s ionosphere.

Coronal mass ejections not only interact with Earth’s 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.