E-Print Archive

There are 4571 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
Solar Radio Spikes and Type IIIb Striae Manifestations of Sub-second Electron Acceleration Triggered by a Coronal Mass Ejection
Statistical study of Type III bursts and associated HXR emissions
On orbit performance of the solar flare trigger for the Hinode EUV Imaging Spectrometer
Plasma Composition Measurements in an Active Region from Solar Orbiter/SPICE and Hinode/EIS
Modulation of cosmic ray anti-protons in the heliosphere: simulations for a solar cycle
Temporal and spatial association between microwaves and type III bursts in the upper corona
Prospective Implications of EUV Coronal Plumes for Magnetic-network Genesis of Coronal Heating, Coronal-hole Solar Wind, and Solar-wind Magnetic-field Switchbacks
Solar Energetic Particle Events with Short and Long Onset Times
The mechanism of magnetic flux rope rotation during solar eruption
Quantification of the Writhe Number Evolution of Solar Filament Axes
Starspot mapping with adaptive parallel tempering. II. Application to TESS data for M-dwarf flare stars, AU Microscopii, YZ Canis Minoris, and EV Lacertae
A Superflare on YZ Canis Minoris Observed by Seimei Telescope and TESS: Red Asymmetry of Hα Emission Associated with White-Light Emission
The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components
Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect
Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013
Spectral and Imaging Diagnostics of Spatially-Extended Turbulent Electron Acceleration and Transport in Solar Flares
Detection of a high-velocity prominence eruption leading to a CME associated with a superflare on the RS CVn-type star V1355 Orionis
Magnetohydrodynamics Instabilities of Double Magnetic Bands in a Shallow-water Tachocline Model: I Cross-equatorial Interactions of Bands
Stability of slow magnetoacoustic and entropy waves in the solar coronal plasma with thermal misbalance
The chromosphere underneath a Coronal Bright Point

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



© 2000-2020 Solar Physics Group - Montana State University