Haerendel, Gerhard | Engineering Papers

DOE OSTI2012

SOLAR AURORAS

This paper deals with the acceleration of high-energy flare electrons by field-parallel electric fields in an approach tailored after the auroral acceleration process. Electromagnetic energy, derived from the release of magnetic shear stresses, is converted into kinetic energy of particles. The stress release is enabled by field-aligned potential drops generated by anomalous resistivity of highly filamentary currents. The high-energy flare electrons are identified with runaway particles of this process. The magnetic shear stresses originate from Alfven waves emitted from high-beta loop-top plasma which is produced by braking of the outflow from a reconnection site higher up in the corona. Partial reflection of the waves at the interface to the chromosphere leads to evaporation of chromospheric plasma and creation of a strongly filamentary structure in the sheared coronal field. The energy conversion process propagates spontaneously, like an erosion process in three dimensions. The overall stress release site forms a thin triangular sheet growing along and perpendicular to the field. After about one second, its cross-section perpendicular to B has grown to tens of square kilometers. This spontaneous growth strongly alleviates the demands on the primary filamentary structure posed by the condition of current criticality. Energy flux and mean energy are of the magnitude typical for hard X-rays producing electrons. Their strong dependence on the ambient magnetic field in combination with the fast propagation of the energy conversion sites could lead to energy-dependent time delays of a few 100 ms, much longer than the time-of-flight effects of the electrons.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

Anomalous plasma diffusion and the magnetopause boundary layer

An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.

Treumann, Rudolf A.↗

NASA NTRS1991

The High Energy Solar Physics mission (HESP): Scientific objectives and technical description

The High Energy Solar Physics mission offers the opportunity for major breakthroughs in the understanding of the fundamental energy release and particle acceleration processes at the core of the solar flare problem. The following subject areas are covered: the scientific objectives of HESP; what we can expect from the HESP observations; the high energy imaging spectrometer (HEISPEC); the HESP spacecraft; and budget and schedule.

Crannell, Carol↗