Coronal loop

In solar physics, a coronal loop is a well-defined arch-like structure in the Sun's atmosphere made up of relatively dense plasma confined and isolated from the surrounding medium by magnetic flux tubes.

Coronal loops begin and end at two footpoints on the photosphere and project into the transition region and lower corona.

They typically form and dissipate over periods of seconds to days[1] and may span anywhere from 1 to 1,000 megametres (621 to 621,000 mi) in length.

A coronal loop occurs when a curved arc of the magnetic field projects through the visible surface of the Sun, the photosphere, protruding into the solar atmosphere.

[7][8] Very high plasma velocities (in the range of 40–60 km/s) have been detected by the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission.

The mission was extended to March 2007 due to its resounding success, allowing SOHO to observe a complete 11-year solar cycle.

In particular, the Extreme ultraviolet Imaging Telescope (EIT) instrument is used extensively in coronal loop observations.

In April 1998, the Transition Region and Coronal Explorer (TRACE) was launched from Vandenberg Air Force Base.

Due to the high spatial (1 arc second) and temporal resolution (1–5 seconds), TRACE has been able to capture highly detailed images of coronal structures, whilst SOHO provides the global (lower resolution) picture of the Sun.