Astron. Astrophys. 358, 741-748 (2000)

Transition region and coronal structuring

E. O'Shea ¹, P.T. Gallagher ^1,2, M. Mathioudakis ¹, K.J.H. Phillips ², F.P. Keenan ¹ and A.C. Katsiyannis <sup>1

1</sup> Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, N. Ireland (E.Oshea@qub.ac.uk; P.Gallagher@qub.ac.uk; M.Mathioudakis@qub.ac.uk; F.Keenan@qub.ac.uk; A.Katsiyannis@qub.ac.uk)
² Space Science Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon. OX11 0QX, UK (phillips@solg2.bnsc.rl.ac.uk)

Received 27 August 1999 / Accepted 17 February 2000

Abstract

In this paper we examine regions of internetwork, network and bright network emission, observed in the quiet Sun with the Coronal Diagnostic Spectrometer (CDS ) onboard SoHO. The slopes of the emission measure distributions, between 5.4 log T_e 6.0, are found to differ in each region, suggesting the presence of different atmospheric structures. From an analysis of emission area the network is shown to have two populations of structures, a low transition region group and a coronal group. Using MDI magnetograms the bright network emission is shown to originate from regions of strong magnetic field composed of bipolar loops and unipolar funnels, that extend from the low transition region up to the corona. Up to 30% of all radiative losses between 5.7 log T_e 6.3 are found to come from these continuous bright network structures. Cross-sectional areas calculated from redshift values suggest that the area expansion seen in the bright network emission is the result of flux tube expansion into the corona, accompanied by either a downflow or upflow of material.

Key words: techniques: image processing methods: observational Sun: corona Sun: transition region Sun: UV radiation Sun: atmosphere

Send offprint requests to: E. O'Shea

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Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. Observations
  • 2.2. Image segmentation
• 3. Results and discussion
  • 3.1. Emission measure distributions
  • 3.2. Filling factors of the emission
  • 3.3. Radiative losses
  • 3.4. Geometry of the emission
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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