heroes

[Norman Albers]

Another hero of mine is Hans Alfven and I just heard on the radio of a report on the solar wind implicating Alfven waves as an acceleration mechanism to get particles up to one or two million miles per hour speed.

[Royston]

Here's an article on the observations confirming the theory...

 

http://www.abc.net.au/science/articles/2007/12/07/2112379.htm?site=science&topic=latest

 

and a more technical explanation of the theory itself here...

 

http://cfa-www.harvard.edu/uvcs/yb/node76.html

[Norman Albers]

Good refs, Snail. I'll read up on my Alfven waves and explain them; it's been a few decades. For scale reference in relativity, a million mph is one or two parts in a thousand compared to lightspeed; [math]\beta[/math]~[math]10^{-3}[/math].

[Norman Albers]

These waves are called hydromagnetic, and arise in a strong B-field, say [math]B_z[/math]. If a small region of neutral plasma is perturbed in the y-direction, both +/- species cross the magnetic field lines, are are moved sideways, in x. They move in opposite senses and so constitute an electric current, and this current will be completed in a larger region above and below, in z. In the initial region, the current produces a reaction against the original magnetic field which tends to restore the original perturbation. This is expressed as a force density of: [math]J\times B[/math]. The outer completion of the current loop reacts in the opposite direction, so you can see wave motion which propagates in z. If I am reading correctly, there is not a characteristic plasma frequency here; what is so is the characterization of a wave phase velocity, [math] v_p= B_0/\sqrt{\mu_0\rho}[/math], while frequency and wavelength are of arbitrary excitation.

[Norman Albers]

I am trying to further my understanding of Alfven, hydromagnetic waves in a plasma. The analysis gives us a phase velocity dependent on magnetic field strength and plasma density. There seems to be no constraint on frequency, except for phenomenologic range. Is the statement that given any perturbation at frequency [math]\omega[/math], there is a damped propagation of inversely proportional wavelength, so the only constant constraint is the phase velocity?

[YT2095]

any idea of What Freq these are at in Mhz Ghz?

Radio Weather is a hobby of mine.

[Norman Albers]

Where is solar radio noise strong? The article speaks of visible, ultrav, and x range observing. What are they seeing??? I don't know much about the whole mix of physics going down here. I am but a purely theoretical physicist. [Purely _-_]

 

I figured at first that this was a resonant phenomenon like electrostatic plasma oscillations which have a more intrinsic characteristic frequency, but it seems not.