  We jointly invert for magnetic and velocity fields at the core surface over
the period 1997-2017, directly using ground-based observatory time series and
measurements from the CHAMP and Swarm satellites. Satellite data are reduced to
the form of virtual observatory time series distributed on a regular grid in
space. Such a sequential storage helps incorporate voluminous modern magnetic
data into a stochastic Kalman filter, whereby spatial constraints are
incorporated based on a norm derived from statistics of a numerical geodynamo
model. Our algorithm produces consistent solutions both in terms of the misfit
to the data and the estimated posterior model uncertainties. We retrieve core
flow features previously documented from the analysis of spherical harmonic
field models, such as the eccentric anti-cyclonic gyre. We find enhanced
diffusion patterns under both Indonesia and Africa. In contrast to a steady
flow that is strong under the Atlantic hemisphere but very weak below the
Pacific, interannual motions appear evenly distributed over the two
hemispheres. Recovered interannual to decadal flow changes are predominantly
symmetrical with respect to the equator outside the tangent cylinder. In
contrast, under the Northern Pacific we find an intensification of a high
latitude jet, but see no evidence for a corresponding feature in the Southern
hemisphere. The largest flow accelerations that we isolate over the studied era
are associated with meanders, attached to the equatorward meridional branch of
the planetary gyre in the Eastern hemisphere, that is l
