E-Print Archive

There are 3882 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
Spontaneous flux concentrations from the negative effective magnetic pressure instability beneath a radiative stellar surface View all abstracts by submitter

Axel Brandenburg   Submitted: 2018-02-03 05:30

Abstract: The formation of sunspots requires the concentration of magnetic flux near the surface. The negative magnetic pressure instability (NEMPI) might be a possible mechanism for accomplishing this, but it has mainly been studied in simple systems using an isothermal equation of state without a natural free surface. We study NEMPI in a stratified Cartesian mean-field model where turbulence effects are parameterized. We use an ideal equation of state and include radiation transport, which establishes selfconsistently a free surface. We use a Kramers-type opacity with adjustable exponents chosen such that the deeper layers are approximately isentropic. No convection is therefore possible in this model, allowing us to study NEMPI with radiation in isolation. We restrict ourselves to two-dimensional models. We use artificially enhanced mean-field coefficients to allow NEMPI to develop, making it therefore possible to study the reason why it is much harder to excite in the presence of radiation. NEMPI yields moderately strong magnetic flux concentrations a certain distance beneath the surface where optical depth is unity. The instability is oscillatory and in the form of upward travelling waves. This seems to be a new effect that has not been found in earlier models without radiative transport. The horizontal wavelength is about ten times smaller than what has been found previously in more idealized isothermal models. In our models, NEMPI saturates at field strengths too low to explain sunspots. Furthermore, the structures appear too narrow and too far beneath the surface to cause significant brightness variations at the radiative surface. We speculate that the failure to reproduce effects resembling sunspots may be related to the neglect of convection.

Authors: Perri, B., & Brandenburg, A.
Projects: None

Publication Status: A&A 609, A99 (2018)
Last Modified: 2018-02-05 22:07
Go to main E-Print page  Evidence For The Magnetic Breakout Model in an Equatorial Coronal-Hole Jet  Powerful Solar Flares of September 2017: Correspondence Between Parameters of Microwave Bursts and Proton Fluxes near Earth  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Key
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
The origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave
Indirect solar wind measurements using archival cometary tail observations
Helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet Sun
Always a Farm Boy
Effect of transport coefficients on excitation of flare-induced standing slow-mode waves in coronal loops
Study of Three-dimensional Magnetic Structure and the Successive Eruptive Nature of Active Region 12371
Statistical study of magnetic non-potential measures in confined and eruptive flares
Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling
Negative flare in the He I 10830 Å line in facula
Time resolved spectroscopic observations of an M-dwarf flare star EV Lac during a flare
Two Episodes of Magnetic Reconnections During a Confined Circular-ribbon Flare
Enhanced stellar activity for slow antisolar differential rotation?
Quasi-periodic pulsations in the most powerful solar flare of Cycle 24
GONG Catalog of Solar Filament Oscillations Near Solar Maximum
Chromospheric response during the precursor and the main phase of a B6.4 flare on August 20, 2005
Unambiguous Evidence of Coronal Implosions During Solar Eruptions and Flares
Two Types of Long-duration Quasi-static Evolution of Solar Filaments
Oscillations of cometary tails: a vortex shedding phenomenon?
Observations of Running Penumbral Waves Emerging in a Sunspot
Reconnection in the Post-Impulsive Phase of Solar Flares

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