Power spectra of Hα Doppler shifts

The temporal characteristics of the chromospheric velocity field in a quiet region are studied by means of a carefully guided sequence of 215 H spectra of the disk centre lasting 54 min. The Doppler shifts of each frame at = 0.4 Å are measured and the velocity history of each position on the sun is reconstructed. The velocity power spectrum is found for each of 256 points along the total slit length of 280000 km.A steady downward velocity is associated with places where the amplitude of the fluctuating velocity is high. The average velocity power spectrum exhibits three main features: (1) A peak at 287 sec, (2) A group of high frequency peaks in the range 150–210 sec, and (3) A low frequency peak with a period of 900 sec.The relationship of these features to the Ca K network is discussed.Member of the High Altitude Observatory Solar Project at Sacramento Peak, on leave from Dunsink Observatory, Ireland.