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Title: Multi-wavelength observations of chromospheric evaporation during the impulsive phase of solar flares
Author: Milligan, Ryan Oliver
ISNI:       0000 0001 3408 1361
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2008
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This thesis presents multi-wavelength observations of both quiescent and active phenomena in the solar corona. Using emission line ratio techniques, a decaying active region was observed over a period of five days and its temperature and density structure were mapped. The mean temperature and density were fouf\d to decrease as the region approached the solar limb. Radiative energy losses were found to dominate over conductive losses by over an order of magnitude thereby providing a proxy for the heating rate. By comparing this heating rate with the corresponding total photospheric magnetic flux, it was concluded that this region was heated by magnetically associated waves, rather than small-scale reconnection events. The majority of this work, however, deals with investigating the dynamic response of the solar chromosphere to energy injected in the form of non-thermal electrons during solar flares. From the analysis of two separate flares, electron beam fluxes that were found to differ by over an order of magnitude were found to produce significantly different responses in the chromosphere as observed by Doppler shifts in EUV emission lines. While upflow velocities of -120 kmls in the 8 MK Fe XIX line were associated with the smaller flare, velocities over a factor of 2 higher were found in the larger event. In addition, these high-velocity upflows were found to be associated with low-velocity downflows as seen in chromospheric and transition region lines. This is due to the overpressure produced in the evaporating material and distinguishes this explosive evaporation from the former gentle case. These findings provide strong observational evidence that the dynamic response of the solar atmosphere is sensitively dependent upon the flux of incident electrons. These findings also suggest that there exists an electron flux threshold beyond which the chromosphere is unable to efficiently radiate the deposited energy.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available