Heating and acceleration processes in hot thermal and impulsive solar flares

Journal Article · Fri Mar 01 04:00:00 EST 1985 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/162992· OSTI ID:5740170

Tsuneta, S

A simple model to describe the unusual characteristics of hot thermal flares as observed with the Hinotori satellite and the overall hard X-ray time evolution of impulsive flare is presented. Unver the assumption of a steady electric field applied by an external driver during the course of flare evolution, it is shown that the plasma density in the energy release site plays an essential role in the mode of energy release. In the impulsive phase, more than 10/sup 35/ electrons s/sup -1/ can run away because of the large ratio (approx.0.3) of the applied electric field to the Dreicer field due to the relatively low background plasma density (n< or =4 x 10/sup 10/ cm/sup -3/). The estimated number of runaway electrons is consistent with the observed thick target flux above 30--40 keV. In the gradual phase, the ratio is reduced to epsilon< or =0.1 by the increase of plasma density (n> or =10/sup 11/ cm/sup -3/) due to the chromospheric evaporation, and Joule heating becomes energetically predominant as compared with particle acceleration. The plasma in the energy-release site is in the classical state throughout the flare, with the possible occurrence of ion-cyclotron turbulence only at the onset of the impulsive phase. For hot thermal flares, a high plasma density probably due to the low-altitude of the flaring loop makes epsilon< or =0.1, resulting in intense Joule heating from the start of the flare without an evident impulsive (acceleration) phase.

• Research Organization: Institute of Apace and Astronautical Science
• OSTI ID: 5740170
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 290:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics &amp; Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACCELERATION
ELECTRIC FIELDS
ELECTRIC HEATING
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HEATING
JOULE HEATING
LEPTONS
MATHEMATICAL MODELS
PLASMA
PLASMA ACCELERATION
PLASMA DENSITY
PLASMA HEATING
RADIATIONS
RESISTANCE HEATING
SOLAR ACTIVITY
SOLAR ELECTRONS
SOLAR FLARES
SOLAR PARTICLES
SOLAR RADIATION
SOLAR X-RAY BURSTS
STAR MODELS
STELLAR RADIATION