Solar cycle variation of the temperature structure within the cores of coronal streamers

¹ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
² Department of Mathematical and Physical Sciences, St Andrews University, Scotland, UK

Corresponding author: C. R. Foley, carl.foley@mssl.ucl.ac.uk

Received: 30 July 2001
Accepted: 8 November 2001

Abstract

We use the Coronal Diagnostic Spectrometer onboard the Solar and Heliospheric Observatory (SOHO) to analyze conditions in coronal streamer structures observed close to solar minimum (1996 July 8) and near maximum (1999 August 5). We measured the intensities of emission lines from Fe IX–XV ions and found the most intense emission to be from Fe XI at solar minimum and from Fe XV at solar maximum. We then used the line ratio method with transitions in selected ions to extract the radial temperature behavior in the structures. The solar minimum peak values were about 1.4 MK at 1.3 , while values derived close to solar maximum were consistent with the Yohkoh observations at the last maximum, displaying an apparently asymptotic temperature of around 2.2 MK above 1.2 . We discuss the observations in relation to possible mechanisms for energy deposition in large coronal structures at different phases of the solar cycle.