[GTP] Seminar at NCAR- Jonathan Pietarila Graham

[Silvia Gentile]

Joint GTP - HAO Seminar

Turbulent Small-scale Dynamo Action in Solar Surface Simulations
Jonathan Pietarila Graham
Max Planck Institute for Solar System Research


The origin of small-scale quiet-Sun intra-network magnetic field is 
unclear.
One possible source is a turbulent small-scale dynamo driven by surface 
convection.  We demonstrate that surface convection in realistic solar 
simulations exhibits such dynamo action.  By presenting a derivation of 
the energy balance equation and transfer functions for compressible 
magnetohydrodynamics (MHD), we can quantify the source of magnetic 
energy on a scale-by-scale basis.  We rule out the two alternative 
mechanisms for the generation of small-scale magnetic field in the 
simulations: the tangling of magnetic field lines associated with the 
turbulent cascade and Alfvenization of small-scale velocity fluctuations 
("turbulent induction'').  Instead, we find the dominant source of 
small-scale magnetic energy is stretching by inertial-range fluid 
motions of small-scale magnetic field lines against the magnetic tension 
force to produce (against Ohmic dissipation) more small-scale magnetic 
field. The scales involved become smaller with increasing Reynolds 
number, which identifies the dynamo as a small-scale turbulent dynamo.


Wednesday, December 9 2009
Center Green Laboratory 1, Room 2126
Lecture 1:30pm