  Triggering process for prominence instability and consequent CMEs is not
fully understood. Prominences are maintained by the Lorentz force against the
gravity, therefore reduction of the prominence mass due to the coronal rain may
cause the change of the force balance and hence destabilisation of the
structures. We aim to study the observational evidence of the influence of
coronal rain on the stability of prominence and subsequent eruption of CMEs. We
used the simultaneous observations from AIA/SDO and SECCHI/STEREO spacecrafts
from different angles to follow the dynamics of prominence/filaments and to
study the role of coronal rain in their destabilisation. Three different
prominences/filaments observed during years 2011-2012 were analysed using
observations acquired by SDO and STEREO. In all three cases massive coronal
rain from the prominence body led to the destabilisation of prominence and
subsequently to the eruption of CMEs. The upward rising of prominences
consisted in the slow and the fast rise phases. The coronal rain triggered the
initial slow rise of prominences, which led to the final instability (the fast
rise phase) after 18-28 hours in all cases. The estimated mass flux carried by
coronal rain blobs showed that the prominences became unstable after 40 \% of
mass loss. We suggest that the initial slow rise phase was triggered by the
mass loss of prominence due to massive coronal rain, while the fast rise phase,
i.e. the consequent instability of prominences, was caused by the torus
instability and/or magnetic reconnection with overlying coronal field.
Therefore, the coronal rain triggered the instability of prominences and
consequent CMEs. If this is the case, then the coronal rain can be used to
predict the CMEs and hence to improve the space weather predictions.
