Finding Alpha

Equilibrium Equation: The forces of gravity and gas pressure can be  neglected in the equilibrium equation of the coronal magnetic structure. This means that J and B are collinear.

Ampere's Law: Neglecting the electric field, the curl of B is proportional to the current density.

Alpha: The curl of B is just B times a scalar value alpha. Alpha is a measure of the helicity of of the magnetic field.

 
 

Mean Alpha: Alpha is calculated at each pixel, and the mean value of the alpha distribution is found. This alpha histogram at time 18:01 on AR8210 shows that alpha is centered closely around zero.





Linear Fit Alpha: Alpha is also calculated by plotting Jz, the vertical current density, versus Bz, the vertical magnetic field, and fitting a line to the plot. Alpha is equal to the slope of the line. Bz and Bt uncertaintiesthresholds were set to minimize noise.



 

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