Moorthy, Sri Ayilavan Thedchana; (1993) Solar maximum mission observations of solar flares. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Soft X-ray observations made by instruments aboard the Solar Maximum Mission satellite are used to investigate the dynamics and energetics of solar flares. The interpretation of the observations is linked to the characteristics of the instruments. The calibration of one of these instruments, the Bent Crystal Spectrometer (BCS), is described and the results of this calibration are used in the work described in the following chapters. It is known that the width of BCS emission lines is affected by the spatial size of flares. This instrumental effect does not contribute much to the already broad rise phase lines, but becomes significant in the decay phase. Flat Crystal Spectrometer (FCS) images of flares are used to estimate, for the first time, the magnitude of this effect. It is found to add no more than 20% to the true non- thermal velocities in the decay phase. If the non-thermal mass motion is due to plasma being constrained to follow the transverse motion of Alfven waves, then the amount of energy available for coronal heating via this transport mechanism can be estimated. Another question regarding the decay phase is whether or not there is flare heating. A simplified hydrodynamical analysis of cooling coronal loops is applied to cooling flare loops seen by the BCS and the FCS to determine which of these flares show signs of decay phase heating. The dynamics of the rise phase of flares may be studied by measuring the widths of emission lines. A novel method of doing this is introduced, and applied to a large sample of flares. It is found that the presence of a substantial amount of slow upflows is required to explain the observed trends in the data.

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