Striation eigenmodes along the geomagnetic field and eigenvalues in the limit of strong ionneutral collisions
Abstract
A secondorder linear differential equation is derived for determining the linear eigenmodes of striation instabilities along the geomagnetic field. Eigenvalues (i.e., temporal frequencies in complex space) are determined along with the eigenmodes. The differential equation includes the contribution of two significant physical effects, ion polarization currents and inductive electric fields. The numerical evaluation of the differential equation emphasizes the collisional limit appropriate to situations when the instabilities are driven at altitudes where the ionneutral collision frequency is much larger than the growth rate for the instability. The numerical results indicate that the instabilities can drive parallel electron currents in the magnetosphere. However, because of finite parallel resistivity, magnetic field lines generally cannot be considered to be equipotentials. It is suggested that the coefficient for ion diffusion resulting from ionneutral collisions plays an important role in determining the maximum perpendicular wave number for which bifurcation is possible. The coefficient for ionneutral diffusion results in a qualitatively and quantitatively meaningful diffusivity for application to the ``Ushaped'' curve description of striation evolution.
 Publication:

Journal of Geophysical Research
 Pub Date:
 March 1985
 DOI:
 10.1029/JA090iA03p02819
 Bibcode:
 1985JGR....90.2819S
 Keywords:

 Geomagnetism;
 Magnetospheric Electron Density;
 Magnetospheric Instability;
 Particle Collisions;
 Differential Equations;
 Eigenvalues;
 Linear Equations;
 Striation;
 Geophysics