Very long period activity at the base of solar wind streams

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

Abstract

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 (≈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 ≈90 min, it is unclear whether these intensity fluctuations are due to waves or are the result of a recurrent magnetic reconnection process.