  We report here the first results of a multi-wavelength campaign focussing on
magnetospheric accretion processes of the classical TTauri star (cTTS)
V2129Oph. In this paper, we present spectropolarimetric observations collected
in 2009 July with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT).
Circularly polarised Zeeman signatures are clearly detected, both in
photospheric absorption and accretion-powered emission lines, from time-series
of which we reconstruct new maps of the magnetic field, photospheric brightness
and accretion-powered emission at the surface of V2129Oph using our newest
tomographic imaging tool - to be compared with those derived from our old 2005
June data set, reanalyzed in the exact same way.
  We find that in 2009 July, V2129Oph hosts octupolar & dipolar field
components of about 2.1 & 0.9kG respectively, both tilted by about 20deg with
respect to the rotation axis; we conclude that the large-scale magnetic
topology changed significantly since 2005 June (when the octupole and dipole
components were about 1.5 and 3 times weaker respectively), demonstrating that
the field of V2129Oph is generated by a non-stationary dynamo. We also show
that V2129Oph features a dark photospheric spot and a localised area of
accretion-powered emission, both close to the main surface magnetic region
(hosting fields of up to about 4kG in 2009 July). We finally obtain that the
surface shear of V2129Oph is about half as strong as solar.
  From the fluxes of accretion-powered emission lines, we estimate that the
observed average logarithmic accretion rate (in Msun/yr) at the surface of
V2129Oph is -9.2+-0.3 at both epochs, peaking at -9.0 at magnetic maximum. It
implies in particular that the radius at which the magnetic field of V2129Oph
truncates the inner accretion disc is 0.93x and 0.50x the corotation radius in
2009 July and 2005 June respectively.
