E-Print Archive

There are 4053 abstracts currently viewable.


Advanced Search
Main Page Add New E-Print Submitter
News Help/FAQ About Preferences
Manage Key Phrase
Observations of conduction driven evaporation in the early rise phase of solar flares View all abstracts by submitter

Marina Battaglia   Submitted: 2009-03-16 07:19

The classical flare picture features a beam of electrons, which were accelerated in a site in the corona, hitting the chromosphere. The electrons are stopped in the dense chromospheric plasma, emitting bremsstrahlung in hard X-rays. The ambient material is heated by the deposited energy and expands into the magnetic flare loops, a process termed chromospheric evaporation. In this view hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from the hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture. For the first time, the pre-flare phase of such solar flares is studied in detail. The aim is to understand the early rise phase of these events. We want to explain the time evolution of the observed emission by means of alternative energy transport mechanisms such as heat conduction. RHESSI events displaying pronounced pre-flare emission were analyzed in imaging and spectroscopy. The time evolution of images and full sun spectra was investigated and compared to the theoretical expectations from conduction driven chromospheric evaporation. The pre-flare phase is characterized by purely thermal emission from a coronal source with increasing emission measure and density. After this earliest phase, a small non-thermal tail to higher energies appears in the spectra, becoming more and more pronounced. However, images still only display one X-ray source, implying that this non-thermal emission is coronal. The increase of emission measure and density indicates that material is added to the coronal region. The most plausible origin is evaporated material from the chromosphere. Energy provided by a heat flux is capable of driving chromospheric evaporation. We show that the often used classical Spitzer treatment of the conductive flux is not applicable. The conductive flux is saturated. During the preflare-phase, the temperature of the coronal source remains constant or increases. Continuous heating in the corona is necessary to explain this observation. The observations of the pre-flare phase of four solar flares are consistent with chromospheric evaporation driven by a saturated heat flux. Additionally, continuous heating in the corona is necessary to sustain the observed temperature.

Authors: Battaglia, M., Fletcher, L., Benz, A. O.
Projects: RHESSI

Publication Status: A&A, accepted
Last Modified: 2009-03-16 11:54
Go to main E-Print page  Relationship between photospheric currents and coronal magnetic helicity for force-free bipolar fields  Solar-Terrestrial Simulation in the STEREO Era: The January 24-25, 2007 Eruptions  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Go to main E-Print pageGo to main E-Print page.
Previous AbstractPrevious Abstract.
Next AbstractNext Abstract.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
View All Abstracts By SubmitterView all abstracts by submitter.
Delete AbstractDelete abstract.

Latest Entries
Linear waves in a non-equilibrium ionisation partially ionised plasma
How Many Twists Do Solar Coronal Jets Release?
Different Signatures of Chromospheric Evaporation in Two Solar Flares Observed with IRIS
The Physical Nature of Spiral Wave Patterns in Sunspots
Predicting Solar Flares Using a Long Short-Term Memory Network
Coronal loop transverse oscillations excited by different driver frequencies
Solar Center-Limb Variation of the Strengths of Spectral Lines: Classification and Interpretation of Observed Trends
The plasmoid instability in a confined solar flare
High-frequency dynamics of active region moss as observed by IRIS
Extreme-ultraviolet Late Phase Caused by Magnetic Reconnection over Quadrupolar Magnetic Configuration in a Solar Flare
Two-step evolution of a rising flux rope resulting in a confined solar flare
Why torus-unstable solar filaments experience failed eruption?
The Magnetic Properties of Heating Events on High-Temperature Active Region Loops
Pulse-beam heating of deep atmospheric layers, their oscillations and shocks modulating the flare reconnection
A potential magnetic field calculator for solar physics applications using staggered grids
E and B polarizations from inhomogeneous and solar surface turbulence
Oscillations Accompanying a He I 10830 Å Negative Fare in a Solar Facula II. Response of the Transition Region and Corona
Flare reconnection-driven magnetic field and Lorentz force variations at the Sun's surface
Why Does the Solar Corona Abnormally Rotate Faster Than the Photosphere?
Impacts On Proton Fluxes Observed During Different Interplanetary Conditions

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey

© 2003 Solar Physics Group - Montana State University