* Astronomy

Members Login
Post Info TOPIC: Alfvén waves


L

Posts: 131433
Date:
RE: Alfvén waves
Permalink  
 


Lab astrophysics aims for the stars

The giant orange magnets were built decades ago to confine hydrogen nuclei in the quest for fusion energy. But since 1998, Jan Egedal, a plasma physicist at the Massachusetts Institute of Technology in Cambridge, has used the magnets, from a massive, doughnut-shaped tokamak, to simulate magnetic fields in the thin wind of charged particles streaming from the Sun. Egedal hopes to learn how the solar wind transfers energy.
Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Alfven Waves in the Solar Atmosphere
Authors: Mihalis Mathioudakis, David Jess, Robertus Erdelyi

Alfven waves are considered to be viable transporters of the non-thermal energy required to heat the Sun's quiescent atmosphere. An abundance of recent observations, from state-of-the-art facilities, have reported the existence of Alfven waves in a range of chromospheric and coronal structures. Here, we review the progress made in disentangling the characteristics of transverse kink and torsional linear magnetohydrodynamic (MHD) waves. We outline the simple, yet powerful theory describing their basic properties in (non-)uniform magnetic structures, which closely resemble the building blocks of the real solar atmosphere.

Read more (2289kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Alfvén Reflection and Reverberation in the Solar Atmosphere
Authors: P. S. Cally

Magneto-atmospheres with Alfvén speed [a] that increases monotonically with height are often used to model the solar atmosphere, at least out to several solar radii. A common example involves uniform vertical or inclined magnetic field in an isothermal atmosphere, for which the Alfvén speed is exponential. We address the issue of internal reflection in such atmospheres, both for time-harmonic and for transient waves. It is found that a mathematical boundary condition may be devised that corresponds to perfect absorption at infinity, and, using this, that many atmospheres where a(x) is analytic and unbounded present no internal reflection of harmonic Alfvén waves. However, except for certain special cases, such solutions are accompanied by a wake, which may be thought of as a kind of reflection. For the initial-value problem where a harmonic source is suddenly switched on (and optionally off), there is also an associated transient that normally decays with time as O(t-1) or O(t-1 ln t), depending on the phase of the driver. Unlike the steady-state harmonic solutions, the transient does reflect weakly. Alfvén waves in the solar corona driven by a finite-duration train of p-modes are expected to leave such transients.

Read more (482kb, PDF)



__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard