  We investigate the structure and dynamics of the magnetospheric accretion
region and associated outflows on a scale smaller than 0.1 au around the young
transitional disk system GM Aur. We monitored the variability of the system on
timescales ranging from days to months, using high-resolution optical and
near-infrared spectroscopy, multiwavelength photometry, and low-resolution
near-infrared spectroscopy, over a total duration of six months (30 rotational
cycles). We analyzed the photometric and line profile variability to
characterize the accretion and ejection processes. The luminosity of the system
is modulated by surface spots at the stellar rotation period of 6.04 days. The
Balmer, Paschen, and Brackett hydrogen lines as well as the HeI 5876 A and HeI
10830 A line profiles are modulated on the same period. The PaB line flux
correlates with the photometric excess in the u' band, which suggests that most
of the line emission originates from the accretion process. High-velocity
redshifted absorptions reaching below the continuum periodically appear in the
near-infrared line profiles at the rotational phase in which the veiling and
line fluxes are the largest. These are signatures of a stable accretion funnel
flow and associated accretion shock at the stellar surface. This large-scale
magnetospheric accretion structure appears fairly stable over at least 15 and
possibly up to 30 rotational periods. In contrast, outflow signatures randomly
appear as blueshifted absorption components in the Balmer and HeI 10830 A line
profiles and disappear on a timescale of a few days. The coexistence of a
stable, large-scale accretion pattern and episodic outflows supports
magnetospheric ejections as the main process occurring at the star-disk
interface. Stable magnetospheric accretion and episodic outflows appear to be
physically linked on a scale of a few stellar radii in this system.
