Somehow, vast amounts of energy leave the Sun’s 6000-K photosphere, rise about 10 thousand kilometers, and heat the corona to 1 million kelvin. Despite the prodigious scales, no one knows exactly how the energy overcomes the thermal gradient to reach the corona or how the energy ultimately thermalizes.
Magnetic fields dominate the energy density of the corona and surely play a leading role in heating it, as figure 1 suggests. But to the continuing frustration of solar physicists, the heating mechanism evidently operates on scales too fine and fast to catch in the act.
In a forthcoming paper, Steven Tomczyk and Scott McIntosh of the National Center for Atmospheric Research in Boulder, Colorado, report a search for one of the contending mechanisms: the magnetohydrodyamic disturbances known as Alfvén waves. 1 The waves show up throughout the NCAR study, but whether they contain enough energy to heat the corona remains...
