35 research outputs found
Acceleration of Relativistic Protons during the 20 January 2005 Flare and CME
The origin of relativistic solar protons during large flare/CME events has
not been uniquely identified so far.We perform a detailed comparative analysis
of the time profiles of relativistic protons detected by the worldwide network
of neutron monitors at Earth with electromagnetic signatures of particle
acceleration in the solar corona during the large particle event of 20 January
2005. The intensity-time profile of the relativistic protons derived from the
neutron monitor data indicates two successive peaks. We show that microwave,
hard X-ray and gamma-ray emissions display several episodes of particle
acceleration within the impulsive flare phase. The first relativistic protons
detected at Earth are accelerated together with relativistic electrons and with
protons that produce pion decay gamma-rays during the second episode. The
second peak in the relativistic proton profile at Earth is accompanied by new
signatures of particle acceleration in the corona within approximatively 1
solar radius above the photosphere, revealed by hard X-ray and microwave
emissions of low intensity, and by the renewed radio emission of electron beams
and of a coronal shock wave. We discuss the observations in terms of different
scenarios of particle acceleration in the corona.Comment: 22 pages, 5 figure
The Origin, Early Evolution and Predictability of Solar Eruptions
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011