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Title: A coupled hydrodynamic and optically-thin radiative emission model for the solar atmosphere
Author: Bradshaw, S. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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A large amount of previous work has assumed that the population of ions comprising the solar atmosphere remain in equilibrium with the temperature of the plasma. However, the characteristic time-scales over which the temperature of the plasma can change during dynamic events has been shown to be shorter than the time-scales of the atomic processes that govern the ion populations. Therefore, the assumption that the ion populations remain in equilibrium with the plasma, regardless of its state, is not valid in all circumstances. This has important consequences for the analysis of observational data and the treatment of radiative emission in theoretical models. Observations depend upon the measurement of the intensity of spectral lines, which in turn depends upon the population of the emitting ions. Invalid assumptions about the processes leading to the measured intensity of a spectral line may lead one to misinterpret the observational data and draw incorrect conclusions concerning the properties of the plasma. The total rate of energy loss by radiation from the plasma can be substantially altered when the population of ions undergo departures from equilibrium. In turn, this affects the energy balance of the plasma and, consequently, its dynamical behaviour. The work presented in this dissertation represents an attempt to address these important considerations through the study of the processes that govern the radiative emission and the development of a suitable treatment to allow non-equilibrium processes to be accounted for in hydrodynamic modelling studies. Observable quantities, such as spectral line intensities, are synthesised from the results and these can be used in the analysis of observational data to allow a more accurate interpretation.  The dynamic modelling studies of the author show that strong departures from equilibrium of the ion populations and the radiative emission occur during many commonly observed events such as cooling, small-scale heating (nanoflares) and solar flares. The departures from equilibrium are shown to influence the properties of the plasma, its dynamical behaviour and the interpretation of observational data. However, they are also shown to provide an explanation for properties of features observed in the solar atmosphere that have not previously been understood.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available