An erupting macrospicule. Characteristics derived from SOHO-CDS spectroscopic observations

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 0.95 x 10⁶ K near the limb to 1.2 x 10⁶ K at about 4.7 x 10⁴ 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 3 x 10⁴ km above the limb. The macrospicule was found to have a density of the order of 10¹⁰ cm^-3 and a temperature of about 2-3 x 10⁵ 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 6 x 10⁴ km.