Coronal Mass Ejections

Introduction

A Coronal Mass Ejection (CME) is a significant release of plasma and accompanying magnetic field from the solar corona. They often follow solar flares and are normally present during a solar prominence eruption. The plasma is released into the solar wind and can be observed in coronagraph imagery.

A photograph of a Coronal Mass Ejection, showing a large, bright, white cloud of plasma being ejected from the surface of the sun.

Formation and Characteristics

CMEs are caused by the release of magnetic energy stored in the sun's coronal magnetic field. This energy can be released via reconnection of magnetic field lines, which can result in the expulsion of plasma and magnetic flux into interplanetary space. The expelled material is a plasma consisting primarily of electrons and protons, but may contain small quantities of heavier elements such as helium, oxygen, and even iron.

The speed of CMEs varies widely, but averages between 20 to 3,200 kilometers per second. The mass of a CME also varies, but typically ranges from 1x10^12 to 1x10^16 grams. The energy involved in a CME is on the order of 1x10^25 joules.

Detection and Monitoring

CMEs are detected and monitored using a variety of space-based observatories. The primary tool for CME detection is the coronagraph, an instrument that blocks out the light from the sun's disk to allow the fainter corona to be observed. The Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) are two of the most important observatories for CME detection.

Impact on Earth and Space Weather

CMEs are a key factor in space weather, which can affect systems on Earth and in space. When a CME impacts the Earth's magnetosphere, it can cause a geomagnetic storm. These storms can cause a variety of effects, including disruptions to radio communications, damage to satellites, and increased radiation levels that can pose a risk to astronauts.

In addition to these practical effects, geomagnetic storms caused by CMEs can also result in beautiful displays of the Northern and Southern Lights.

Historical Observations and Notable Events

CMEs have been observed for centuries, with the earliest recorded observations dating back to the 1700s. However, it was not until the advent of space-based observatories in the 20th century that their true nature and importance were understood.

One of the most notable CME events in history is the Carrington Event of 1859, which caused widespread disruption to telegraph systems and resulted in auroral displays as far south as the Caribbean.

Future Research and Understanding

Despite the progress that has been made in understanding CMEs, there is still much that is not known. Future research will focus on improving our understanding of the mechanisms that cause CMEs, as well as improving our ability to predict them. This research is crucial for mitigating the potential impacts of CMEs on our increasingly technology-dependent society.