An erupting macrospicule

Characteristics derived from SOHO-CDS spectroscopic observations

Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK

Corresponding author: S. Parenti, sparenti@uclan.ac.uk

Received: 9 November 2001
Accepted: 20 December 2001

Abstract

We report results from the analysis of a sequence of SOHO/CDS observations obtained off-limb in the south polar coronal hole on 6 March 1998. Three successive data sets were obtained with the Normal Incidence Spectrometer (NIS), the first of which showed a jet-like feature visible in the chromospheric and low transition region lines. The morphological characteristics of this feature suggested it was a macrospicule. The two remaining observations of the same region indicated a quiet coronal hole with a density of 10⁸ cm^-3 and a temperature rising from  K near the limb to  K at about  km above the limb. These data were averaged and used as “background” for the macrospicule observation. The resulting subtracted spectra showed more details of the feature. In particular, a cloud of plasma was detected at about  km above the limb. The macrospicule was found to have a density of the order of 10¹⁰ cm^-3 and a temperature of about  K. The initial outflow velocity near the limb was over 80 km s^-1. This decreased to a terminal value of 26 km s^-1 above about  km.