Heating of the Magnetically Closed Corona and Physical Models of Solar and Stellar Spectral Irradiances
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James A Klimchuk↗
Engineering topics
Adrian Daw
Publications and source records attributed to Adrian Daw.
Observing Coronal Microscales and Their Connection With Mesoscales
Why the Sun has a tenuous upper atmosphere some 1000 times hotter than the photosphere is a fundamental open problem in space plasma physics despite decades of study. A leading hypothesis, supported by indirect evidence, is that in most of the corona heating is confined to narrow current sheets in which energy is dissipated despite the low large-scale resistivity of the coronal plasma. Although the kinetic scales of reconnection or wave heating are beyond remote observation, thermal structure on scales ≲100 km are expected to be produced by the primary heating mechanisms operating within a filamentary magnetic field. This white paper considers what could be learned from direct observations of coronal plasma on those scales and outlines a mission concept that is more fully described in a Heliophysics Mission Concept Study for the Coronal Microscale Observatory.
Douglas Rabin↗
Application of EUV and SXR Spectra from the EUNIS Sounding Rocket to Solar Coronal Heating
The nanoflare model is among the most actively investigated approaches to the longstanding problem of solar coronal heating. According to this model, the ~2 MK corona is heated by numerous tiny impulsive heating events, each of which is too small to be detected individually. Evidence for nanoflares is faint emission from small amounts of plasma at flare-like temperatures (4-10 MK) in non-flaring regions. The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument was designed to investigate coronal heating by observing emission lines of Fe XVIII, whose maximum ionization fraction occurs at temperatures around 7.1 MK, and Fe XIX (8.9 MK). Although expected to be faint, emission from hot plasma to which these lines are sensitive provides compelling evidence for the nanoflare model. EUNIS observes spectral line emission at 92-115 A in 3rd order, 277-344 A in 1st order, and 530-640 A in 1st order. These wavebands include lines from Fe XVIII and Fe XIX, as well as lines from ions formed over a wide range of lower temperatures (0.1-3.5 MK). We present preliminary results for a quiescent solar active region observed during the flight of 2021 May 18.
ultraviolet radiation↗