X28 (now, maybe X45), huge X-type flare--5,000 Solar X-ray luminosity; 11/06/2003.

Solar Flares

Solar flares are violent explosions in the Sun's atmosphere releasing as much as 6x10²⁵ Joules over a few minutes. The Sun produces around 4x10²⁹ Joules in 15 minutes. Flares can heat the Solar gases to 10 million Kelvin and produces EM radiation from the radio to the gamma-rays in addition to ejecting material into space. Flares typically occur in active regions (sunspot groups) on the Sun. They are thought to tap the energy of the intense magnetic fields associated with Sunspots.

Sunquake generated by a Solar Flare.

Solar flares are associated with active regions on the Sun. Solar flares are classified according to their brightness in x-rays. There are 3 categories: X-class flares are big; events which trigger radio blackouts on the Earth. M-class flares are medium-sized flares which can have effects on the Earth. C-class flares are small with few noticeable effects on the Earth.

Coronal Mass Ejections (CMEs) and Solar Flare Ejections

CMEs are large bubbles of gas (protons and electrons) containing up to 100 billion kg of mass, ejected from the Sun on time scales of hours. They are often associated with solar flares and eruptive prominences but they can alos occur without associated flares or prominences. They apparently are related to solar flares but are not caused by them. CMEs travel at high speeds, 20 km/s to 2,700 km/s, and can reach the Earth after several days. When CMEs strike the Earth, they can initiate large geomagnetic storms which have caused power outages and damaged communications. See a video showing one months of CMEs here.
Some Solar flares have produced ejections which travel at nearly the speed of light and have reached the Earth within 15 minutes of the event. Large Solar flares and their ejections can cause disruptions of the ionosphere of the Earth and lead to large scale disruptions in communications.

CMEs and the high speed flows from the Sun after Solar flares strike the Earth's magnetosphere (cocoon) and compress and form shock waves. The intense flow of charged particles and magnetic field from the Sun can cause huge currents to flow in the Earth's magnetosphere which can lead to power outages and the high energy particles can disrupt the upper atmospheric layer of the Earth known as the Ionospere which can disrupt long-range communications on the Earth.

The above are exampls of Aurorae. Aurorae are produced by the charged particles mainly electrons but some protons which leak into the Earth's magnetosphere. They drift to the magnetotail where they are accelerated (from energy generated by magnetic reconnection). The high energy particles interact with atoms and molecules in the Earth's upper atmosphere (at heights > 80 km). The green and red light mainly comes from excited oxygen. Some of the lower level greenish, bluish, and pinkish glows come ionic nitrogen and molecular nitrogen.