Time series study of EUV spicules observed by SUMER/SoHO

¹ CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, Univ. of Science and Technology of China, Hefei, Anhui 230026, PR China e-mail: xld@ustc.edu.cn
² Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland e-mail: [mdp;jgd]@arm.ac.uk
³ Astronomical Institute of the Romanian Academy, 75212 Bucharest 28, Romania
⁴ Sect. of Astrophysics, Astronomy and Mechanics, Dept. of Physics, Univ. of Athens, Athens 15783, Greece

Received: 21 December 2004
Accepted: 18 April 2005

Abstract

Here we study the dynamic properties of EUV spicules seen at the solar limb. The selected data were obtained as time series in polar coronal holes by SUMER/SoHO. The short exposure time and the almost fixed position of the spectrometer's slit allow the analysis of spicule properties such as occurrence, lifetime and Doppler velocity. Our data reveal that spicules occur repeatedly at the same location with a birth rate of around 0.16/min as estimated at 10´´ above the limb and a lifetime ranging from 15 down to ≈3 min. We are able to see some spicules showing a process of “falling after rising” indicated by the sudden change of the Doppler velocity sign. A periodicity of ≈5 min is sometimes discernible in their occurrence. Most spicules have a height between 10´´ and 20´´ above the limb. Some can stretch up to 40´´; these “long macro-spicules” seem to be comprised of a group of high spicules. Some of them have an obvious periodicity in the radiance of ≈5 min.