Doppler velocity variations based on the height above the visible limb of the Sun

The goal of this study is to analyze Doppler velocity fluctuations and their relation to height from the solar limb. The focus is on spicular dynamics in the solar polar region using high-resolution observations from Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). By analyzing the Mg II k line, which is sensitive to chromospheric and transition region dynamics, we obtained Doppler velocities to examine plasma motions. The results revealed symmetric Doppler shifts of  ± 30 km/s, indicating rotating spicules, as well as very high velocities of 60–70 km/s in dynamic spicules, which are higher than the usual 20–30 km/s reported in previous studies. Furthermore, our diagrams and plots reveal that spicule Doppler velocities are not uniform but exhibit a multi-velocity nature with at least three distinguished peaks along their axis, indicating intrinsic non-uniform dynamics along their axis—a novel phenomenon confirmed through detailed analysis ruling out observational artifacts. These results imply greater magnetic interactions or enhanced Alfvén wave activity at higher altitudes. The discussion touches upon the multicomponent stratification of the solar atmosphere, in which velocity fluctuations are correlated with variations in temperature, density, and opacity. The faster speeds at polar latitudes highlight their contribution to propelling rapid solar winds.