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We study the height variations of the sizes of chromospheric andtransition-region features in a small coronal hole and the adjacent quiet Sun,considering images of the intensity, Doppler shift, and non-thermal motion ofultraviolet emission lines as measured by SUMER, together with the magneticfield as obtained by extrapolation from photospheric magnetograms. In order toestimate the characteristic sizes of the different features present in thechromosphere and transition region, we have calculated the autocorrelationfunction for the images as well as the corresponding extrapolated magneticfield at different heights. The HWHM of the autocorrelation function isconsidered to be the characteristic size of the feature shown in thecorresponding image. Our results indicate that, in both the coronal hole andquiet Sun, the HWHM of the intensity image is larger than that of the images ofDoppler-shift and non-thermal width at any given altitude. The HWHM of theintensity image is smaller in the chromosphere than in the TR, where the sizesof intensity features of lines at different temperatures are almost the same.But in the upper part of the transition region, the intensity size increasesmore strongly with temperature in the coronal hole than in the quiet Sun. Wealso studied the height variations of the HWHM of the magnetic field magnitudeB and its component |Bz|, and found they are equal to each other at a certainheight below 40 Mm in the coronal hole. The height variations of the HWHM of|Bz/B| seem to be consistent with the temperature variations of the intensitysize. Our results suggest that coronal loops are much lower, and magneticstructures expand through the upper TR and lower corona much more strongly withheight in the coronal hole than in the quiet Sun.

Sizes of transition-region structures in coronal holes and in the quiet Sun