THE EVERSHED EFFECT IN PENUMBRAL FINE-STRUCTURES .1. HEIGHT DEPENDENCE OF VELOCITY FLUCTUATIONS

A number of spectral lines with negligible Zeeman splitting have been used for a spectroscopic observation of sunspot penumbrae at different slit positions and heliocentric angles: Fe I 5576 simultaneously with Si I 6145, and, separately, Fe I 5434 and Ni I 5435 simultaneously wi th Ni I 4912. The formation levels of cores and wings at 20% depressio n were determined from contribution functions to the line depression. The spatial fluctuations of the continua, the residual line intensitie s, and the Doppler shifts of cores and wings are separated from a mean penumbral variation. A power spectrum analysis shows that the typical spatial scale of both the velocity and the intensity fluctuations inc reases with height. The rms velocity fluctuations decrease with height , resembling the known granular behaviour. The coincidence of a coarse r spatial intensity and velocity structure and smaller velocities at h igher levels favour an explanation by a height dependent filling.