  Most models of solar eruptions assume that coronal field lines are anchored
in the dense photosphere and thus the photospheric magnetic fields would not
have rapid, irreversible changes associated with eruptions resulted from the
coronal magnetic reconnection. Motivated by the recent work of Hudson, Fisher &
Welsch (2008) on quantitatively evaluating the back reaction due to energy
release from the coronal fields, in this Letter we synthesize our previous
studies and present analysis of new events about flare-related changes of
photospheric magnetic fields. For the 11 X-class flares where vector
magnetograms are available, we always find an increase of transverse field at
the polarity inversion line (PIL) although only 4 events had measurements with
1 minute temporal resolution. We also discuss 18 events with 1 minute cadence
line-of-sight magnetogram observation, which all show prominent changes of
magnetic flux contained in the flaring Delta spot region. Except in one case,
the observed limb-ward flux increases while disk-ward flux decreases rapidly
and irreversibly after flares. This observational evidence provides support,
either directly or indirectly, for the theory and prediction of Hudson, Fisher
& Welsch that the photospheric magnetic fields must respond to coronal field
restructuring and turn to a more horizontal state near the PIL after eruptions.
