Observations of the temperature, density and velocity structure of the solar corona

Details Observations of the temperature, density and velocity structure of the solar corona Observations of the temperature, density and velocity structure of the solar corona

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt.........5o&link_type=abstract

PhD Dissertation, Colorado Univ. Boulder, CO United States

Physics

Solar Corona, Electron Density (Concentration), Photosphere, Solar Physics, Heating, Atmospheric Temperature, Synchrotron Radiation, Spectral Resolution, Luminous Intensity, Radiation Sources

Scientific paper

The solar corona exists at a temperature of over 106 K while the underlying visible surface, the photosphere, is much cooler, about 6,000K. How this tenuous outer layer can be many orders of magnitude hotter than the photosphere is one of the principal enigmas of solar physics. Various mechanisms have been proposed to explain coronal heating, but none have been completely successful in accounting for its observed characteristics. It is the purpose of this thesis to present observations of both the large scale velocity structure and the small scale density and temperature structure of the quiet corona which will constrain theories of coronal heating. Spatially resolved spectra of the solar corona were obtained in the extreme ultraviolet during a sounding rocket experiment on June 20, 1989. In order to obtain an accurate photometric calibration of the spectrometer, we developed a new technique using a synchrotron radiation source operated by the National Institute for Standards and Technology. With this calibration, along with the high spectral resolution and on-board wavelength calibration capability of the payload, we were able to develop a detailed picture of the density and velocity structure of a portion of the solar corona. Data from the sounding rocket experiment were then compared to white light observations made by the Mk-3 coronagraph operated by the High Altitude Observatory at Mauna Loa. The white light continuum intensity of the solar corona is proportional to the mean electron density along the line of sight, whereas the emission line intensity is proportional to the average value of the electron density squared. By comparing these two data sets, we find that the density irregularity factor is close to unity for the quiet corona. The irregularity analysis in this thesis is the first to consider the possibility of a non-isothermal corona. We also find that the systematic velocity structure seen in the transition region is not present in the solar corona.

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