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In April 1967 five Nike‐Apache rockets were launched from Kiruna, Sweden, carrying barium release and electron concentration experiments. The component of the electric field transverse to the magnetic lines of force is derived from the motion of the ion clouds. The electron concentration measurements provide ionospheric conductivities. The magnitudes of the electric fields varied between 2 and 20 v/km. Their directions were northwestward for evening conditions and southwestward for morning conditions. The magnetic perturbations on the ground that would result from ionospheric currents derived on the basis of the measured fields and conductivities closely resemble the actual ground magnetometer data. The electric fields vary appreciably with space and time; they can even reverse their directions over distances of the order of 60 km.

The Alfvén critical velocity mechanism for ionization of a neutral gas streaming across the magnetic field has been demonstrated in laboratory experiments. In March 1983, two rocket‐borne experiments with Ba and Sr tested the effect in the wall‐less laboratory of space from Punto Lobos, Peru, near 430 km altitude. “Star of Lima” used a conical Ba shaped charge aimed at an instrument payload about 2 km away. Because of rocket overperformance the detonation occurred in partial sunlight, so that less than 21.6% of the ionizing UV was present. As discussed in other papers in this series, particle and field measurements indicate the production of hot electrons and waves in the energy and frequency range respectively predicted to produce a cascade of ionization by the Alfvén mechanism. However, the ionization fluxes and wave energy density did not reach cascade levels, and optical observations indicate that only 2.5 to 5×1020 Ba ions were produced. A substantial portion and perhaps all of the ionization could have been produced by solar UV. The failure of the Alfvén process in this experiment is not well understood.