Observational evidence for coronal mass injection by ``evaporation" of spicular plasma

Abstract

Despite being a common feature of the solar chromosphere, spicules are still a poorly understood phenomenon. Not much is known about their impact on the physics of the transition region and corona, for which spicules are believed to be the dominant mechanism for mass injection. We recently observed the spatial plasma structure of polar spicules in a large temperature range with the EUV spectrometer SUMER onboard the SOHO spacecraft. The spectrometer slit was placed tangentially to the polar limb at various projected heights < 22\arcsec. Our spectra in the wavelength range of 748-792 { Angstroms} simultaneously record emission lines which are formed in a wide temperature range between 30 000 and 600 000 K.We find that the typical structure of spicular plasma grows, horizontally and vertically, with increasing emission-line temperature, reaching ~ 20\arcsec at 1 - 2* 10(5) K. This suggests an ``evaporation" of spicular plasma into the transition region (TR) and corona, for which we find further evidence from an emission measure analysis.