Figure 1 illustrates how magnetic energy is tranferred upward from the Sun's surface toward the corona above. There is more than enough energy coming up from the loops of the "magnetic carpet" to heat the corona. These dramatic new observations have been made by the Solar Oscillations Investigation (SOI) group at Lockheed-Martin Solar and Astrophysics Laboratory and at Stanford University.
The interaction between the plasma and the magnetic field in the solar corona determines what kind of phenomena will occur in the corona. An unbalanced magnetic flux causes the magnetic field lines to open and a so called coronal hole (CH) is formed. From the CHs a fast stream of plasma (the solar wind) expands into the interplanetary space. From the so called coronal streamers (CSs) a slow stream of plasma is thought to expand into the interplanetary space. Plumes, outside the coronal holes, have also recently been suggested as sources of the slow solar wind. The fast solar wind catches up with the slow solar wind and an interaction region is produced.
Observations with the use of instruments aboard NASA's Spartan 2001 spacecraft and SOHO suggest a new acceleration mechanism of the solar wind. The electrical charges of the solar wind spiral out along the magnetic field in the corona (especially coronal holes). When the magnetic field lines vibrate, as they do in a magnetic wave, the spiraling particles accelerate out and away from the Sun into the interplanetary space.
Figure 5 shows how the solar wind particles are accelerated as the particle spiraling out of from the corona along vibrating magnetic field lines. (Courtesy of NASA Spartan and ESA/SOHO).
The closed magnetic field loops, located below the CSs, can start to expand into, or be explosively ejected into interplanetary space. A so called transient coronal mass ejection (CME) has occurred, which produces an enormous plasma cloud in the interplanetary space. These clouds reach Earth already within 1-2 days. They can involve 1016 g (ten billions tons) gas thas is suddenly ejected at speed up to 2000 km/s with kinetic energy of 1032 ergs. The most intense effects on earth are associated with these fast plasma clouds. They cause interplanetary shocks, large solar particle events (SEP) and non-recurrent geomagnetic storms. In the article Solar energetic particles: A paradigm shift D. V. Reames describes how proton events and CME-Driven shocks are related.
It is believed that solar flares are a result of a sudden (a few minutes to few tens of minutes) release of energy (up to 1032 ergs with temperatures of 10-20 million degrees) stored in the magnetic fields that thread the solar corona in active regions around sunspots. Solar flares produce radiation from longest wavelength radio waves to shortest gamma rays. Solar flares affect ionosphere and radio communication at earth, and also release energetic particles.
Figure 14 shows the solar eclipse of 18 March 1988 in white light (Courtesy of HAO).
Stanford Solar Center.