The sequence of images shown above spans more than a nine
hour period from 12:07 to 21:20 Universal Time (UT), (7:07am
to 4:20pm central daylight savings time). The data include two
M-class flares: an M6.4 flare starting at 13:53 UT and ending
at 15:27 UT; and an M3.2 flare starting at 16:53 UT and ending
at 18:01 UT.
The H-alpha images are displayed in the left-hand panel of
the animation. The magnetic field measurements are displayed
on top of the H-alpha image in the right-hand panel. The solid
lines are "neutral lines" that separate areas with
opposite magnetic polarity (positive from negative or north from
south). The tickmarks point in the direction of the horizontal,
or transverse, component of the magnetic field. Normally the
transverse field is directed across (or perpendicular to) the
neutral lines so that the magnetic field lines travel from the
positive polarity regions directly to the negative polarity regions.
In this example we see several areas where the tickmarks are
directed almost parallel to the neutral lines. The magnetic field
is said to be sheared in these regions.
Over the last few years we have found that flaring activity
is closely associated with sheared magnetic fields. Measurements
of magnetic shear in and around sunspots allows us to predict
the occurence of many large solar flares.