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We have employed a penumbral model, that includes the Evershed flow andconvective motions inside penumbral filaments, to reproduce the azimuthalvariation of the net circular polarization (NCP) in sunspot penumbrae atdifferent heliocentric angles for two different spectral lines. The theoreticalnet circular polarization fits the observations as satisfactorily as penumbralmodels based on flux-tubes. The reason for this is that the effect ofconvective motions on the NCP is very small compared to the effect of theEvershed flow. In addition, the NCP generated by convective upflows cancels outthe NCP generated by the downflows. We have also found that, in order to fitthe observed NCP, the strength of the magnetic field inside penumbral filamentsmust be very close to 1000 G. In particular, field-free or weak-field filamentsfail to reproduce both the correct sign of the net circular polarization, aswell as its dependence on the azimuthal and heliocentric angles.

Convective motions and net circular polarization in sunspot penumbrae