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Astron. Astrophys. 349, 956-960 (1999)


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Coronal hole diagnostics out to [FORMULA]

J.G. Doyle, L. Teriaca and D. Banerjee

Armagh Observatory, College Hill, Armagh BT61 9DG, Ireland (jgd, lte, dipu@star.arm.ac.uk)

Received 27 November 1998 / Accepted 27 May 1999

Abstract

The Si VIII line width measurements and [FORMULA] estimates based on SUMER observations are combined with LASCO and UVCS output to provide an overview of its variations with height above a polar coronal hole. From the combined dataset we find a radial dependence of the electron density, in the range 1-2 [FORMULA] as [FORMULA], from 2 to 4 [FORMULA] as [FORMULA] and then as [FORMULA]. Combining the Si VIII half width at 1/e of the peak intensity with the UVCS O VI half width, we find a small increase of the half width from 1 to 1.2 [FORMULA], then a plateau until 1.5 [FORMULA], thereafter a sharp increase until 2 [FORMULA], finally a more gradual increase reaching 550 km s-1 at 3.5 [FORMULA]. Our data suggests that the MHD waves responsible for the excess line broadening tends to become non-linear as it reaches 1.2 [FORMULA].

Key words: waves – Sun: corona – Sun: UV radiation

Send offprint requests to: J.G Doyle

© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999

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