Temporal variability in the Doppler-shift of solar transition region lines

¹ Armagh Observatory, College Hill, Armagh, BT61 9DG, N. Ireland
² Center for Space Environment Modeling, 1414 Space Research Building, The University of Michigan, Ann Arbor, MI 48109-2143, USA
³ Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁴ Sect. of Astrophysics, Astronomy and Mechanics, Dept. of Physics, Univ. of Athens, Athens 15783, Greece e-mail: madj@star.arm.ac.uk; iroussev@umich.edu; lte@arcetri.astro.it

Corresponding author: J. G. Doyle, jgd@star.arm.ac.uk

Received: 19 December 2001
Accepted: 19 September 2002

Abstract

High cadence datasets taken in C iii 977 Å, O  vi 1032 Å and Ne viii 720 Å were analysed in an effort to establish the extent of the variability in the Doppler-shift of typical mid-transition region lines. The shortest time-scale variability seems to occur in the network boundary regions where the line-shift can vary by 7–8 km  in less than 1 min. The internetwork region also shows variability although this tends to be longer lived, ~2–3 min. The average line-shift in C iii is a red-shift which ranges from ~2 km  to ~20 km  with an average value for all regions selected being around 10 km  in very good agreement with that derived by others. The red-shift values indicate a clear difference between network and internetwork regions, with the largest red-shift being present at the network boundary. For O vi, this gives an average red-shift ranging from 5 to 10 km . For Ne viii, there is a 13 km  difference between internetwork and bright network plasma with the bright network being more red-shifted. This could imply that the bright network regions are dominated by spicule down-flow. In the second part we present results from 2-dimensional (2D) dissipative magnetohydrodynamic (MHD) simulations of the response of the solar transition region to micro-scale energy depositions. A variety of temperatures at which the energy deposition takes place as well as the amount of energy deposited are examined. This work is a continuation of previous related simulations where small-scale energy depositions were modelled in 1D hydrodynamics. The observable consequences of such transient events are then computed for three transition region lines, namely C iv 1548 Å, O vi 1032 Å, and Ne viii 770 Å, under the consideration of non-equilibrium ionization.