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Astrophysics Research Centre

School of Mathematics and Physics

The Anomalous Temporal Behaviour of Lyman-alpha Emission During Solar Flares Using SDO/EVE

  • Submitted by: Ryan Milligan, Queen's University Belfast/NASA
  • Authors: R. Milligan
  • Session: Tuesday afternoon posters.

Despite being the most prominent emission line in the solar spectrum, there has been a notable lack of studies devoted to variations in chromospheric Lyman-alpha (Lyα) emission during solar flares in recent years. The few examples that do exist, however, claim Lyα emission to be a substantial radiator of the total energy budget of solar flares (on the order of 10%). It is also a known driver of density fluctuations in earth's ionosphere. The EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory now provides broadband (~100Å), photometric Lyα data at 10 s cadence, and has observed scores of solar flares in the 5 years since it was launched. However, the time profiles appear to display rise times of tens of minutes around the time of the flare onset. This is in stark contrast to the rapid, impulsive increase observed in other intrinsic chromospheric features (H-alpha, Lyman-beta, Lyman Continuum, C III, etc.). Furthermore, Lyα emission peaks around the time of the peak of thermal soft X-ray emission, rather than during the impulsive phase when energy deposition in the chromosphere - often assumed to be in the form of nonthermal electrons - is greatest. The time derivative of Lyα lightcurves also closely resembles that of the time derivative of soft X-rays, rather reminiscent of the Neupert Effect. To establish whether this atypical behaviour is a characteristic of flare heating in the lower solar atmosphere during explosive events, or a manifestation of the broadband nature of the EVE observations, comparisons have been made with spectrally-resolved Lyα measurements during flares from SORCE/SOLSTICE, and other broadband photometers such as PROBA2/LYRA and GOES/EUVS-E.

public/hinode9/schedule/session-04p/v0070.txt · Last modified: 2015/07/30 01:08 (external edit)

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