Cross‐Field Instability for the Formation of Sporadic E

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Abstract
The cross‐field instability is an important process in the explanation of small‐scale sporadic E. Differences in the theories presented by different authors are apparent. It is true that there is no one‐to‐one correspondence of each Fourier component of perturbation between the electric field and the electron density about the direction of the ambient density gradient. The question arises as to how to choose properly the perturbation in the ambient charge gradient; but the difficulty does not seem serious. Computer experiments using realistic perturbations are desirable for the final answer on this question. The short‐circuiting effect along the geomagnetic field does not damp the electrical polarization with small transverse size, i.e., small east‐west wavelength. The upper limit of this size is a few hundred meters.