  Classical T Tauri stars (CTTSs) are young low-mass stellar objects accreting
mass from their circumstellar disks. They are characterized by high levels of
coronal activity as revealed by X-ray observations. This activity may affect
the disk stability and the circumstellar environment. Here we investigate if an
intense coronal activity due to flares occurring close to the accretion disk
may perturb the inner disk stability, disrupt the inner part of the disk and,
possibly, trigger accretion phenomena with rates comparable with those
observed. We model a magnetized protostar surrounded by an accretion disk
through 3D magnetohydrodinamic simulations. We explore cases characterized by a
dipole plus an octupole stellar magnetic field configuration and different
density of the disk or by different levels of flaring activity. As a result of
the simulated intense flaring activity, we observe the formation of several
loops that link the star to the disk; all these loops build up a hot extended
corona with an X-ray luminosity comparable with typical values observed in
CTTSs. The intense flaring activity close to the disk can strongly perturb the
disk stability. The flares trigger overpressure waves which travel through the
disk and modify its configuration. Accretion funnels may be triggered by the
flaring activity, thus contributing to the mass accretion rate of the star.
Accretion rates synthesized from the simulations are in a range between 10^-10
and 10^-9M_sun yr^-1 The accretion columns can be perturbed by the flares and
they can interact with each other, possibly merging together in larger streams.
As a result, the accretion pattern can be rather complex: the streams are
highly inhomogeneous, with a complex density structure, and clumped
