What are Coronal Mass Ejections (CMEs)?

Sept. 18, 2023

Recently, Earth was hit by a strong Coronal Mass Ejection (CME).

About Coronal Mass Ejections (CMEs):

  • CMEs are large expulsions of plasma and magnetic fields from the Sun’s corona that propagate outward into interplanetary space.
  • During a CME, the Sun releases a colossal amount of material, including electrons, protons, and heavier ions, as well as magnetic fields. This ejected material travels at high speeds into space.
  • Causes:
    • CMEs are typically triggered by the destabilisation of the Sun's magnetic fields.
    • The exact mechanisms are complex, but they often involve the reconfiguration or disruption of magnetic loops on the Sun's surface.
  • CMEs are distinct from solar flares, although they often occur together. Solar flares are sudden and intense bursts of energy and radiation, whereas CMEs involve the expulsion of solar material.
  • Impact on Earth:
    • Geomagnetic Storms: The interaction between the CME's magnetic fields and Earth's magnetosphere can lead to geomagnetic storms. These can disrupt satellite communications, navigation systems, and even power grids.
    • Auroras: CMEs can cause spectacular displays of the Northern and Southern Lights, also known as auroras, by energising particles in Earth's atmosphere.
    • Radiation Hazards: Astronauts in space or passengers on high-altitude flights can be exposed to elevated levels of radiation during a CME event.

Key Facts about Solar Flare:

  • A solar flare is an intense burst of radiation coming from the release of magnetic energy associated with sunspots.
  • Flares are our solar system’s largest explosive events.
  • They are seen as bright areas in the sun, and they can last from minutes to hours.
  • In a matter of just a few minutes, they heat the material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, including from radio waves to x-rays and gamma rays.
  • Although solar flares can be visible in white light, they are often more readily noticed via their bright X-ray and ultraviolet emissions.
  • Effect of Solar Flare on Earth:
    • The intense radiation emitted during a solar flare can affect satellite communications, disrupt radio signals, and even pose a risk to astronauts in space.
    • Additionally, the increased solar radiation can lead to geomagnetic storms, which may impact power grids and cause auroras (northern and southern lights) at lower latitudes.

What is a Geomagnetic Storm?

  • A geomagnetic storm is a major disturbance of Earth's magnetosphere.
  • These storms result from variations in the solar wind that produce significant changes in the currents, plasmas, and fields in Earth’s magnetosphere.
  • The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several hours) periods of the high-speed solar wind and a southward-directed solar wind magnetic field (opposite the direction of Earth’s field) at the dayside of the magnetosphere.
  • The largest such storms are associated with solar coronal mass ejections (CMEs), where a billion tons or so of plasma from the sun, with its embedded magnetic field, arrives at Earth.