  Sunspot penumbrae show high-velocity patches along the periphery. The
high-velocity downflow patches are believed to be the return channels of the
Evershed flow. We aim to investigate their structure in detail using Hinode
SOT/SP observations. We employ Fourier interpolation in combination with
spatially coupled height dependent LTE inversions of Stokes profiles to produce
high-resolution, height-dependent maps of atmospheric parameters of these
downflows and investigate their properties. High-speed downflows are observed
over a wide range of viewing angles. They have supersonic line-of-sight
velocities, some in excess of 20km/s, and very high magnetic field strengths,
reaching values of over 7 kG. A relation between the downflow velocities and
the magnetic field strength is found, in good agreement with MHD simulations.
The coupled inversion at high resolution allows for the accurate determination
of small-scale structures. The recovered atmospheric structure indicates that
regions with very high downflow velocities contain some of the strongest
magnetic fields that have ever been measured on the Sun.
