An erupting macrospicule: characteristics derived from SOHO-CDS spectroscopic observations

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 $0.95 \times 10^6$ K near the limb to $1.2 \times 10^6$ K at about $4.7 \times 10^4$ 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 $3 \times 10^4$ km above the limb. The macrospicule was found to have a density of the order of 1010 cm-3 and a temperature of about $2{-}3 \times 10^5$ 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 $6 \times 10^4$ km