Irregularities in the equatorial ionosphere: The Berkner Symposium

The main results of the symposium, which dealt with both E and F region irregularities, are summarized and discussed. The basic processes generating the E region (electrojet) irregularities now seem to be understood, but the details are not. Linear plasma instability theory appears to account for the presence or absence of irregularities. However, the irregularity amplitudes, the wavelength distribution, the propagation velocities, etc., all of which depend on nonlinear effects, are not well explained. The question of nonlinear mechanisms is controversial and is being attacked from a number of directions. The F region irregularities are still poorly understood; the basic driving mechanisms are not yet established. Two new ideas that seem promising involve (1) a gravitational interchange instability involving entire magnetic tubes of force and (2) irregular ‘fingers’ of metallic ions extending into the lower ionosphere that alter the E × B drift patterns.