The author thanks P. Testa, S. Orlando, G. Peres, J. Klimchuk, and the anonymous referees for
suggestions. The author acknowledges support from the Italian Ministero dell’Università e della Ricerca.
The Transition Region and Coronal Explorer (TRACE) is a mission of the Stanford-Lockheed Institute for
Space Research, and part of the NASA Small Explorers
program. The solar X-ray images of Figure 2
from the Yohkoh mission of ISAS, Japan. The X-ray Telescope was prepared by the Lockheed-Martin Solar
and Astrophysics Laboratory, the National Astronomical Observatory of Japan, and the University of Tokyo
with the support of NASA and ISAS. SDO is the first mission launched for NASA’s Living With a Star