cmes

Coronal mass ejections (CMEs) are large eruptions of magnetized plasma from the Sun’s corona. CMEs eject billions of tons of solar material into interplanetary space with embedded magnetic fields. They typically have masses around 10^12 to 10^13 kilograms and travel at speeds from about 200 to over 2,000 kilometers per second. Their angular extent can be wide, and when directed toward Earth they may appear in coronagraph images as a halo around the Sun.

CMEs are connected with various solar eruptive phenomena, including eruptive prominences and solar flares, but a CME can occur without a strong flare. They propagate through the solar wind as interplanetary CMEs (ICMEs) and may develop a distinct magnetic structure known as a magnetic cloud.

Observations are made with space- and ground-based instruments. Coronagraphs (for example, SOHO/LASCO) image CMEs by blocking the bright solar disk. Heliospheric imagers on missions such as STEREO track CMEs through the inner solar system. In situ measurements by spacecraft like WIND, ACE, and Parker Solar Probe sample the plasma and magnetic field as CMEs pass by.

Earth-directed CMEs interact with the Earth's magnetosphere, triggering geomagnetic storms, auroras, and radiation hazards for astronauts. They can disrupt satellite operations, radio communications, and navigation, and in some cases induce currents in power grids. Transit times from the Sun to Earth range from about 15 to 60 hours, depending on speed and geometry.

Prediction relies on solar observations to identify CMEs and their kinematics, combined with models of the solar wind and interplanetary magnetic field. Space weather centers issue alerts when Earth-directed CMEs are detected or anticipated.