A study of a macro-spicule and a transition region explosive event in a solar coronal hole

Abstract

Aims

Spicules and the higher macro-spicules (jet-like structures seen at the solar limb) are believed to be the dominant mechanism for mass ejection in the higher solar atmosphere outside active regions. But what is the connection between them and other small-scale structures in the Sun’s atmosphere, like for example transition region explosive events, is not known yet.

Methods

Our data are temporal series spectroheliograms of EUV emission lines from two ions (N IV 765 Å and Ne VIII 770 Å), taken with the SUMER (Solar UV Measurements of Emitted Radiation) spectrograph on SoHO (the Solar and Heliospheric Observatory). SUMER’s good spatial, spectral and temporal resolution allowed us to have one of the most detailed studies of these small-scale structures over a range of transition region temperatures.

Results

Our study reveals that a macro-spicule seen off-limb looks similar to a transition region explosive event, especially in the map of the lines’ full-width-at-half-maximum (FWHM). The macro-spicule seen in the low transition region N IV line (≈140,000 K) is also visible in the higher temperature Ne VIII line (≈630,000 K). Also, the jet seen on-disk in the N IV line heats and accelerates plasma to the higher Ne VIII temperature, traveling probably along the local (presumably open) magnetic field line.