Chromospheric evaporation velocities in solar flares

Journal Article · Fri Jun 15 04:00:00 EDT 1984 · Astrophys. J., Lett. Ed.; (United States)

DOI:https://doi.org/10.1086/184290· OSTI ID:6663447

Fisher, G H; Canfield, R C; McClymont, A N

We show that an upper limit to chromosphere evaporation velocities in solar flare loops is approximately 2.35c/sub s/, where c/sub s/ is the sound speed in the evaporated material. Observed upward velocities greater than this limit would imply the existence of additional nonhydrodynamic forces. Hydrodynamic calculations of collisional heating by nonthermal energetic electrons (thick-target model) yield upward velocities near the upper limit at large (> or =3 x 10/sup 10/ ergs s/sup -1/ cm/sup -2/) energy flux values. At more modest fluxes (10/sup 9/-10/sup 10/ ergs s/sup -1/), both ''thermal'' and ''thick-target'' models yield maximum velocities that are between 10% and 30% of the upper limit. Observations of postulated evaporation velocities from the Solar Maximum Mission (Antonucci and Dennis) appear to be between 10% and 25% of the upper limit. When both temperature and velocity of the evaporated plasma are considered, the ''thermal'' model with energy fluxes between 3 x 10/sup 9/ and 10/sup 10/ ergs s/sup -1/ cm/sup -2/ is found to be most consistent with these observations.

• Research Organization: Center for Astrophysics and Space Sciences, University of California, San Diego
• OSTI ID: 6663447
• Journal Information: Astrophys. J., Lett. Ed.; (United States), Journal Name: Astrophys. J., Lett. Ed.; (United States) Vol. 281:2; ISSN AJLEA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALINE EARTH METALS
ATMOSPHERES
CALCIUM
CHROMOSPHERE
COLLISIONAL HEATING
CORRELATIONS
DATA
DIFFERENTIAL EQUATIONS
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
EQUATIONS
EQUATIONS OF MOTION
EVAPORATION
EXPANSION
FERMIONS
FLUID MECHANICS
HEATING
HIGH-FREQUENCY HEATING
HYDRODYNAMICS
INFORMATION
IONIZING RADIATIONS
LEPTONS
MACH NUMBER
MAGNETIC-PUMPING HEATING
MATHEMATICS
MECHANICS
METALS
NUMERICAL ANALYSIS
NUMERICAL DATA
PARTIAL DIFFERENTIAL EQUATIONS
PHASE TRANSFORMATIONS
PLASMA
PLASMA HEATING
RADIATION FLUX
RADIATIONS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR CORONA
SOLAR FLARES
STELLAR ATMOSPHERES
STELLAR CORONAE
TEMPERATURE EFFECTS
TEMPERATURE GRADIENTS
TEMPERATURE MEASUREMENT
THEORETICAL DATA
THERMAL EXPANSION
VELOCITY
X RADIATION