I wish to thank all the many people and institutions that with their support helped me during the course of my PhD. These include, with no particular order:

my first and second supervisors, Barbara and Gordon Bromage for their support and guidance throughout this period.

The University of Central Lancashire for a three-year full-time research studentship, which supported my work and living expenses during that time. In particular, the Centre for Astrophysics for additional financial support for some of my trips.

All the local organising committees and agencies (NATO in particular) that funded my many trips to summer schools, meetings, and congresses.

Deianira. Without her help during the last year, I would have not been able to finish on time.

Barbara Hassall and Ken Phillips for having accepted the task of examining me, and for reading this rather long thesis.

Massimo Landini for his precious collaboration and support from the very beginning.

Enrico Landi, a good collaborator and companion during the many conferences I went to.

Helen Mason, Ken Dere and Peter Young for stimulating discussions and collaborations.

Andy Adamson and Pete Newman, for their continuous support as system managers, during a difficult period including office and building moves and disruptions. [Much of the data reduction, processing and analysis detailed in this thesis has been done with the Interactive Data Language (IDL) and using STARLINK facilities].

The whole of the CDS operation staff at RAL (UK) and GSFC (USA) for their assistance and hospitality during visits there. In particular: Richard Harrison and Dave Pike for their assistance in the planning and execution of the observations; Bob Bentley, without whom most of the Elephant's Trunk coronal hole observations would have not been taken place; Andrzej Fludra, for the stimulating collaboration in working with CDS and in producing results. William Thompson, Eddie Breeveld for their technical support.

Stein Vidar Haugan, for his much appreciated support regarding CDS data analysis and IDL programming.

Sarah Gibson and Douglas Biesecker for the collaboration for the Whole Sun Month Campaign, and support for the attendance of the related workshops.

Barbara Thompson and the EIT consortium for providing the EIT images.

Marta, for her continuous moral support and great long-distance long-lasting friendship.

Vincenzo, for his excellent hospitality and friendship.

Susanna, for an excellent friendship and for cheering me up when I needed.

All the many colleagues and friends, with whom I shared an enjoyable social life in these years. These include (it is virtually impossible to mention all of them): Christophe, Fiona, Eleonora, Andy, Alessandro, Agostino, Vinicio, Katerina, Marianna, Dalila, Nathalie, Turandot, Julia, John, Francesca, Bill, Gabriel, Cormac, Carl, Guillaume, Till, Emmanuel, Carina, Chris, Mark, Pete, Laurence, Lucia, Barbara, Alice, Mikko, Pedro, Maria (2).

I would also like to thank Janey. With her, I learned much, including english.

Finally, I thank my father and all my family, for their help and support when I needed it.

This thesis is dedicated to the memory of Brunella Monsignori Fossi.
She suddenly died the morning of monday 22nd January 1996, in front of her terminal. She spent long part of her active life studying the coronae of cool stars and the sun, and in the last years in preparation for SOHO. I had the opportunity, working closely with her, in Arcetri, to appreciate her qualities outside research.
She would have very much enjoyed studying the solar corona with SOHO and CDS, as I did.

In the following, you can find links to the (g-zipped) postscript files of each Chapter. Note that:

• The postscript files were created in order to be printed in duplex.
• The links to the Sections are not active yet.

• Most contents of the thesis are not published elsewhere, so the proper reference is

  G. Del Zanna, PhD thesis, Univ. of Central Lancashire UK (1999)

• Contents.
  This file contains the above abstract, the acknowledgments and the contents.
• Introduction
  • An introduction to the theory of emission from coronal plasmas
    • Temperature determination
    • Electron density estimates
    • General considerations of the plasma equations
  • Previous observations of the solar corona
    • Ground and space observations of the solar corona
      • Space observations pre-SOHO
      • Space observations: SOHO
    • General coronal hole characteristics
    • Temperatures
      • Temperatures from in-situ charge state measurements
      • Temperatures above the limb from white light observations
      • Temperatures from Ly_a profiles
      • Limb observations from EUV intensities
      • Disc observations and emission measure analysis
      • Temperatures from filter ratio techniques
    • Densities
    • Element abundances
    • Coronal plumes
      • pre-SOHO observations.
      • Theoretical models.
      • SOHO observations
• Critical discussion of spectroscopic diagnostic techniques and their application to CDS data
  Note: Some contents of this Chapter have been published in various journals.
  • Electron density diagnostics
    • Comments on the lines in Table 2.1
    • Some other density-sensitive ratios with problems
    • Concluding comments
  • The L-function method of determining electron density
  • The electron temperature evaluation. The isothermal case
  • The electron temperature evaluation. The DEM method
    • The inversion technique developed to calculate the DEM
  • A comparison of various emission measure methods, using Skylab coronal hole data
    • Some historical approaches. The EM_L, EM_T, DEM_L approximations
      • The emission measure loci approach
      • The Pottasch (19663) approach
      • The Jordan (1971) approximation
      • A different approach. The DEM_L method
    • Results of the DEM approach, basic definitions and comparison with the DEM_L method.
    • The element abundances evaluation. Comparison of the DEM with the DEM_L method.
    • Discussion of the results and comparison with previous analyses
      • The shape of the DEM and the element abundances
      • The problem with the Li-like ions and other lines
  • The element abundance evaluation. Critical discussion of previous work and assessment of the CDS possibilities
    • The potential of CDS for determining abundances
• The CDS instrument. Data analysis and calibration
  Note: Most contents of this Chapter have been published in A&A.
  The second order GIS calibration presented here was offset by a factor of two. This has been corrected in the paper.
  • The normal incidence spectrometer
    • Subtraction of the CCD bias
    • Cosmic ray removal
    • Corrections for flat-fielding, burn-in and nonlinear effects, using VDS_CALIB
    • Correction for geometric distortions, using VDS_ROTATE
    • Spatial resolution and binning along the slit
    • Line-fitting
    • Error estimates.
    • The intensity calibration
  • The grazing incidence spectrometer
    • Fixed patterning and line profiles
    • Ghosts
    • The wavelength calibration
    • The intensity calibration
  • The first-light GIS observations
  • The calibration of the CDS instrument
    • The diagnostic method for the CDS calibration
      • The diagnostic method
      • Applicability of the method
    • Layout of the rest of Section 3.4
    • The SERTS-89 spectrum
    • A GIS internal intensity calibration study
      • The GIS study presented in Landi etal (1999a)
      • The revision of the active region spectrum
    • The NIS observations for the internal intensity calibration
      • The on-disc active region observation of 25th September 1997
    • The observations for the NIS-GIS cross-calibration
      • The rationale for special observing sequences
      • Observation sequences and data analysis
      • The overlapping regions between the CDS channels
      • The lines of the same ion seen in different channels
      • Ghosting and the reconstruction of some lines
      • The NIS and GIS spectra of the quiet sun observations
    • The physical characteristics of the off-limb (1997 May 4) and on-disc (1997 October 16) regions
    • The NIS 1 internal calibration
    • The NIS 2 internal calibration (first order)
      • The transition region and chromospheric lines
      • The coronal lines
      • Other lines
      • Concluding comments on the NIS 1 and NIS 2 sensitivities
    • The cross-calibration between all the NIS and GIS channels, first and second order
      • Cross-calibration between the NIS 1 and GIS 2
      • Cross-calibration between NIS 1 and GIS 1
      • Cross-calibration between NIS 1 and GIS 3
      • Cross-calibration between the NIS 1 and NIS 2
      • On-disc cross-calibration between NIS 2, GIS 3, GIS 4
      • Cross-calibration between NIS 1 and GIS 4 (first and second order)
      • Other cross-calibrations (first and second order)
      • Final results and comments
    • The off-limb observation of May 4th 1997. The effect of different calibrations and ionization equilibrium calculations. Full list of identified lines
      • A comparison of different ionization equilibrium calculations
      • The line identifications and the theoretical spectra
      • The GIS ghosts
    • The on-disc observation of October 16th 1997. Full list of identified lines
      • The GIS ghosts
• Observations and data analysis
  • Some of the CDS studies used or developed
  • The observations during August-September 1996
    • The Whole Sun Month (WSM) campaign
    • The Elephant's trunk
  • The observations during September-October 1997
  • Off-limb observations of polar holes (February - April and October 1997)
  • The software developed for the data analysis
• Results for coronal holes, quiet sun and plumes
  Note: Some contents of this Chapter have been published in various journals.
  • General characteristics of off-limb densities and temperatures for the quiet sun and polar coronal holes from 1996 to 1998
    • Off-limb observations of the equatorial regions
    • Polar coronal holes
  • Results from near-disc-centre observations, 1996 August
    • The results from the Elephant's Trunk observations of the 26th August 1996
    • Results from the quiet sun reference observation - 1996, Aug 25
    • Coronal hole and plume densities, temperatures and abundances - 1996 August 27
      • The spectra and DEM of the Elephant's Trunk coronal hole
      • The DEM of the low-latitude plume
      • The GIS E-W scan across the hole: abundance variations
      • An example of coronal hole GIS spectra
    • Intercomparison and summary of the near-disc-centre results
• Results for polar coronal holes and polar plumes
  Note: Some contents of this Chapter have been published in various journals.
  • On-disc observations of polar holes
    • The October 10th 1997 observations of a polar coronal hole region, with a plume, quiet sun, and a bright point
    • Observations of the quiet sun - coronal hole boundary
  • Off-limb observations of polar holes and plumes
    • The off-limb coronal hole observations of the 12th of September 1997
    • The off-limb observations of 1998 February 9
    • The GIS cross
  • Polar plumes observed on-disc
    • Results for a polar plume observed on 1996 August 23
    • Results for a polar plume observed on 1997 October 11
      • The DEM of the plume area
    • Comparison of GIS spectra with EIT (1997 October 11 data)
• Conclusions and further work
  • Summary of results and conclusions
    • Spectroscopic diagnostic methods and the CDS
    • Solar physics results and conclusions
      • Coronal hole plumes
  • Further work
    • Atomic physics studies
    • Short-time-scale events
    • Coronal holes, the transition region and the plumes
• References
• Appendices
  • The results for SERTS-89
  • The CDS observations (1996-1998)
  • The calibration of the CDS instrument
    • The observations for the CDS calibration
    • The spectra and line identifications for the off-limb observation - May 4th 1997
      • The GIS ghosts for the off-limb observation - May 4th 1997
    • The spectra and line identifications for the on-disc observation - October 16th, 1997
      • The GIS ghosts for the on-disc observation - October 16th 1997
  • Appendix to Chapter 5. CDS spectra of the Elephant's Trunk coronal hole
  • Appendix to Chapter 6
    • Spectra and line identifications - plume observation - October 11th 1997
  
  

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  Giulio Del Zanna May 2003