  It is recently noted that solar eruptions can be associated with the
contraction of coronal loops that are not involved in magnetic reconnection
processes. In this paper, we investigate five coronal eruptions originating
from four sigmoidal active regions, using high-cadence, high-resolution
narrowband EUV images obtained by the Solar Dynamic Observatory (SDO}). The
magnitudes of the flares associated with the eruptions range from the
GOES-class B to X. Owing to the high-sensitivity and broad temperature coverage
of the Atmospheric Imaging Assembly (AIA) onboard SDO, we are able to identify
both the contracting and erupting components of the eruptions: the former is
observed in cold AIA channels as the contracting coronal loops overlying the
elbows of the sigmoid, and the latter is preferentially observed in warm/hot
AIA channels as an expanding bubble originating from the center of the sigmoid.
The initiation of eruption always precedes the contraction, and in the
energetically mild events (B and C flares), it also precedes the increase in
GOES soft X-ray fluxes. In the more energetic events, the eruption is
simultaneous with the impulsive phase of the nonthermal hard X-ray emission.
These observations confirm the loop contraction as an integrated process in
eruptions with partially opened arcades. The consequence of contraction is a
new equilibrium with reduced magnetic energy, as the contracting loops never
regain their original positions. The contracting process is a direct
consequence of flare energy release, as evidenced by the strong correlation of
the maximal contracting speed, and strong anti-correlation of the time delay of
contraction relative to expansion, with the peak soft X-ray flux. This is also
implied by the relationship between contraction and expansion, i.e., their
timing and speed.
