E-Print Archive

There are 3784 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
Slow-Mode MHD Wave Penetration into a Coronal Null Point due to the Mode Transmission  

Andrey Afanasyev   Submitted: 2016-06-22 02:41

Recent observations of magnetohydrodynamic oscillations and waves in solar active regions revealed their close link to quasi-periodic pulsations in flaring light curves. The nature of that link has not yet been understood in detail. In our analytical modelling we investigate propagation of slow magnetoacoustic waves in a solar active region, taking into account wave refraction and transmission of the slow magnetoacoustic mode into the fast one. The wave propagation is analysed in the geometrical acoustics approximation. Special attention is paid to the penetration of waves in the vicinity of a magnetic null point. The modelling has shown that the interaction of slow magnetoacoustic waves with the magnetic reconnection site is possible due to the mode transmission at the equipartition level where the sound speed is equal to the Alfvén speed. The efficiency of the transmission is also calculated.

Authors: Andrey Afanasyev and Arkadiy Uralov
Projects: None

Publication Status: published in Solar Physics
Last Modified: 2016-06-22 09:11
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Cut-off period for slow magnetoacoustic waves in coronal plasma structures  

Andrey Afanasyev   Submitted: 2015-09-27 23:26

Context. There is abundant observational evidence of longitudinal compressive waves in plasma structures of the solar corona, which are confidently interpreted in terms of slow magnetoacoustic waves. The uses of coronal slow waves in plasma diagnostics, as well as analysis of their possible contribution to coronal heating and the solar wind acceleration, require detailed theoretical modelling. Aims. We investigate the effects of obliqueness, magnetic field, and non-uniformity of the medium on the evolution of long-wavelength slow magnetoacoustic waves guided by field-aligned plasma non-uniformities, also called tube waves. Special attention is paid to the cut-off effect due to the gravity stratification of the coronal plasma. Methods. We study the behaviour of linear tube waves in a vertical untwisted straight field-aligned isothermal plasma cylinder. We apply the thin flux tube approximation, taking into account effects of stratification caused by gravity. The dispersion due to the finite radius of the flux tube is neglected. We analyse the behaviour of the cut-off period for an exponentially divergent magnetic flux tube filled in with a stratified plasma. The results obtained are compared with the known cases of the constant Alfvén speed and the pure acoustic wave. Results. We derive the wave equation for tube waves and reduce it to the form of the Klein?Gordon equation with varying coefficients, which explicitly contains the cut-off frequency. The cut-off period is found to vary with height, decreasing significantly in the low-beta plasma and in the plasma with the beta of the order of unity. The depressions in the cut-off period profiles can affect the propagation of longitudinal waves along coronal plasma structures towards the higher corona and can form coronal resonators.

Authors: A.N. Afanasyev, V. M. Nakariakov
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2015-09-28 16:18
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics  

Andrey Afanasyev   Submitted: 2012-05-28 03:11

We present the results of analytical modelling of fast-mode magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider both a linear wave and a weak shock and analyse their behaviour in cold and warm plasmas. We apply the nonlinear geometrical acoustics method based on the Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using the ray approximation and the laws of solitary shock wave damping. We find that a complex caustic is formed around the null point. Plasma heating is distributed in space and occurs at a caustic as well as near the null point due to substantial nonlinear damping of the shock wave. The shock wave passes through the null point even in a cold plasma. The complex shape of the wave front can be explained by the caustic pattern.

Authors: A.N. Afanasyev and A.M. Uralov
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2012-05-29 16:22
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Coronal Shock Waves, EUV waves, and their Relation to CMEs. II. Modeling MHD Shock Wave Propagation Along the Solar Surface, Using Nonlinear Geometrical Acoustics  

Andrey Afanasyev   Submitted: 2011-04-19 20:05

We model the propagation of a coronal shock wave, using nonlinear geometricalacoustics. The method is based on the Wentzel-Kramers-Brillouin (WKB) approachand takes into account the main properties of nonlinear waves: i) dependence ofthe wave front velocity on the wave amplitude, ii) nonlinear dissipation of thewave energy, and iii) progressive increase in the duration of solitary shockwaves. We address the method in detail and present results of the modeling ofthe propagation of shock-associated extreme-ultraviolet (EUV) waves as well asMoreton waves along the solar surface in the simplest solar corona model. Thecalculations reveal deceleration and lengthening of the waves. In contrast,waves considered in the linear approximation keep their length unchanged andslightly accelerate.

Authors: A. N. Afanasyev, A. M. Uralov
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-04-20 13:56
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Slow-Mode MHD Wave Penetration into a Coronal Null Point due to the Mode Transmission
Cut-off period for slow magnetoacoustic waves in coronal plasma structures
Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics
Coronal Shock Waves, EUV waves, and their Relation to CMEs. II. Modeling MHD Shock Wave Propagation Along the Solar Surface, Using Nonlinear Geometrical Acoustics

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