We analyze in detail the penumbral structure found in a recent radiative MHD simulation .
Near \tau = 1 , the simulation produces penumbral fine structure consistent with the observationally inferred interlocking comb structure .
Fast outflows exceeding 8 \mbox { km s } ^ { -1 } are present along almost horizontal stretches of the magnetic field ; in the outer half of the penumbra , we see opposite polarity flux indicating flux returning beneath the surface .
The bulk of the penumbral brightness is maintained by small-scale motions turning over on scales shorter than the length of a typical penumbral filament .
The resulting vertical rms velocity at \tau = 1 is about half of that found in the quiet Sun .
Radial outflows in the sunspot penumbra have two components .
In the uppermost few 100 km , fast outflows are driven primarily through the horizontal component of the Lorentz force , which is confined to narrow boundary layers beneath \tau = 1 , while the contribution from horizontal pressure gradients is reduced in comparison to granulation as a consequence of anisotropy .
The resulting Evershed flow reaches its peak velocity near \tau = 1 and falls off rapidly with height .
Outflows present in deeper layers result primarily from a preferred ring-like alignment of convection cells surrounding the sunspot .
These flows reach amplitudes of about 50 \% of the convective rms velocity rather independent of depth .
A preference for the outflow results from a combination of Lorentz force and pressure driving .
While the Evershed flow dominates by velocity amplitude , most of the mass flux is present in deeper layers and likely related to a large-scale moat flow .