Heating the solar corona
(PHYSorg.com Space & Earth)

The hot outer layer of the sun, the corona, has a temperature of over a million degrees Kelvin, much more than the surface temperature of the Sun which is only about 5500 degrees Kelvin. Moreover, the corona is very active and ejects a wind of charged particles at a rate equivalent to about one-millionth of the moon`s mass each year. Some of these particles bombard the Earth, producing auroral glows and occasionally disrupting global communications. There are two important, longstanding, and related questions about the corona that astronomers are working to answer: how is it heated to temperatures that are so much hotter than the surface? And how does the corona produce the wind?