  Solar eruptions generally refer to coronal mass ejections (CMEs) and flares.
Both are important sources of space weather. Solar flares cause sudden change
in the ionization level in the ionosphere. CMEs cause solar energetic particle
(SEP) events and geomagnetic storms. A flare with unusually high intensity
and/or a CME with extremely high energy can be thought of examples of extreme
events on the Sun. These events can also lead to extreme SEP events and/or
geomagnetic storms. Ultimately, the energy that powers CMEs and flares are
stored in magnetic regions on the Sun, known as active regions. Active regions
with extraordinary size and magnetic field have the potential to produce
extreme events. Based on current data sets, we estimate the sizes of
one-in-hundred and one-in-thousand year events as an indicator of the
extremeness of the events. We consider both the extremeness in the source of
eruptions and in the consequences. We then compare the estimated 100-year and
1000-year sizes with the sizes of historical extreme events measured or
inferred.
