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A burst of X rays was observed at balloon altitude over Alaska with the onset of a sudden commencement geomagnetic storm at 0146 UT on June 27, 1960. The electron bombardment of the upper atmosphere that gave rise to the X rays occurred on a large scale, ionospheric absorption coincident with the X‐ray burst being observed by riometers in Alaska, Sweden, and Norway.

As a result of the IGY riometer program, it has been found that the measurement of ionospheric absorption in arctic regions is a sensitive method of detecting low‐energy cosmic rays associated with solar flares. The normal morphology of these events is described, and details are given of the 24 such events that have been detected in the period from May 1957 through July 1959. Two features have been noted: an apparent asymmetry in the distribution of cosmic‐ray‐producing flares across the solar disk; a pronounced degree of uniformity in the distribution of the radio‐wave absorption over the terrestrial polar cap. These features are discussed, and tentative explanations are suggested.

Further laboratory measurements of the beam‐plasma discharge (BPD) produced when an energetic electron beam traverses an initially neutral gas are presented. The experimental data indicate that the critical beam current Ic at energy V, magnetic field B, and system length L required for ignition obeys the empirical relationship Ic ∝ V3/2/B0.7 PL at pressures P < 2 × 10−5 torr. This relationship appears to primarily describe the accumulation of ambient plasma density, collisionally produced by the beam itself, to a critical value where ωpe² ≈ ωce² at which ignition occurs. Additional measurements of the narrow‐band cyclotron‐related waves (fce < f < 1.4fce) observed at beam currents below BPD threshold do not clearly establish whether this instability is a necessary precursor to the BPD. The relevance of these experiments to past and planned electron beam experiments in space is briefly discussed.

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