EDP Sciences
Free access
Volume 442, Number 3, November II 2005
Page(s) 1087 - 1090
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20053714

A&A 442, 1087-1090 (2005)
DOI: 10.1051/0004-6361:20053714

Very long period activity at the base of solar wind streams

M. D. Popescu1, 2, D. Banerjee3, E. O'Shea1, J. G. Doyle1 and L. D. Xia4

1  Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
    e-mail: [mdp;eos;jgd]@arm.ac.uk
2  Astronomical Institute of the Romanian Academy, 040557 Bucharest 28, Romania
3  Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
    e-mail: dipu@iiap.res.i
4  School of Earth and Space Sciences, Univ. of Science and Technology of China, Hefei, Anhui 230026, PR China
    e-mail: xld@ustc.edu.cn

(Received 28 June 2005 / Accepted 18 July 2005)

Using time series data of spectral lines originating from a wide range of temperatures in the solar transition region, above a polar coronal hole, from SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SoHO (Solar and Heliospheric Observatory), we report on the detection of very long ($\approx$170 min) periodic intensity fluctuations, above the limb. Our data also reveal long periodicities (10-90 min), previously observed with other SoHO instruments. With the acoustic cut-off frequency implying a maximum allowable period of $\approx$90 min, it is unclear whether these intensity fluctuations are due to waves or are the result of a recurrent magnetic reconnection process.

Key words: Sun: solar wind -- Sun: transition region -- Sun: corona

© ESO 2005