Quote:
Scientists previously thought steady heating explained the corona's high temperature, but this model requires that a coronal loop of a given length and temperature should have a specific density, whereas the new evidence shows that they have much higher density than the steady heating model predicts. By considering nanoflares as an alternative explanation, the observed density can be explained.
Read the full article at:
http://www.astronomynow.com/news/n0908/17sun/
of coarse its also because photons can move faster in the less dense corona than in the photosphere which is a much higher density. Its important to know that this increase in speed will also hike up the temperature, but now we substantial evidence that nanoflares contribute to the rise as well
