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Title: Variation of line widths in polar off-limb regions
Authors: Banerjee, D
O'Shea, E
Doyle, J. G
Keywords: Polar Off-Limb Regions;Dynamic Sun;Observations;Solar Physics
Issue Date: Dec-2005
Publisher: European Space Agency
Citation: D. Danesy, S. Poedts, A. De Groof and J. Andries., eds., Proceedings of the 11th European Solar Physics Meeting "The Dynamic Sun: Challenges for Theory and Observations" (ESA SP-600). 11 - 16 September 2005, pp. 43 - 48
Abstract: Using measurement from the Coronal Diagnostic Spectrometer (CDS) on board SOHO we seek to examine the relative roles of radiative and Collisional excitation in regions far off-limb at the Northern pole of the sun. We study the line width variation with height. It is found that above 1150 arcsec the second ratio of two coronal Mg X resonance lines reduces to values that we might expect for a radiatively dominant excitation mode. A comparison of line widths with the Mg X ratios shows that the line widths start to show a decrease in their values at the same location where the dominant excitation changes from being collisionally to radiatively dominant. This is considered to be evidence for a sudden drop in the electron density at this location, and, therefore, the reported tributed to a reduction in the measurable contribution of waves/turbulence to the non-thermal velocity component of the line widths. This result suggests that the reported decrease of line widths in coronal ions at large altitudes off-limb may not simply be related to the dissipation of wave energy. Implication to the acceleration of the fast solar wind will be discussed.
ISSN: 92-9092-911-1
Appears in Collections:IIAP Publications

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