Two new types of low‐frequency noise, designated ‘broadband’ and ‘highpass’ have been detected in the distant magnetosphere by the VLF/LF experiment on the OGO 1 satellite. Broadband noise extends over the entire range of observations from 0.2 to 100 kHz and the intensity decreases with increasing frequency. It occurs in bursts having durations of a few minutes or less. It shows no connection with any of the expected plasma cutoff or resonance frequencies and is believed to be a nonpropagating disturbance generated in the vicinity of the satellite. Highpass noise extends from a characteristic low‐frequency cutoff to above 100 kHz and occurs in bursts lasting tens of minutes. This cutoff has only been observed above 20 kHz. Above the cutoff the intensity shows little variation with frequency. Both types of noise are observed predominantly at L greater than 5 in or near the night hemisphere. The occurrence of both types of noise is highly correlated with the auroral electrojet index. Several times noise bursts began within 2 min of the onset of micropulsations in the polar region even though the satellite was near apogee (24 earth radii). The peak rms magnetic intensity in a highpass noise burst has a maximum of 8×10−5 γ Hz1/2 and averages 10−5 γ Hz−1/2. In free space these magnetic intensities correspond, respectively, to 10−12 and 3×10−14 watt m−2 Hz−1. The peak levels of both types of noise are 3 or more orders of magnitude stronger than emissions from extraterrestrial sources observed with interplanetary probes.

Observations of the free atomic sodium layer near 90 km have been made as part of performance tests on a tunable dye‐laser radar. Altitude profiles of the layer obtained during parts of four nights in the fall of 1971 are consistent with those obtained by other groups but show two interesting additional features. The first is a sharp decrease in density that terminates the layer on the bottom side at a variable altitude near the mesopause. This decrease appears to become sharp only some time after twilight, suggesting that the sodium consumption mechanism undergoes a change as the nighttime chemistry is established. The second feature is a fourfold increase in sodium‐layer content during a 4‐hour period surrounding the transit of the radiant of the Geminids meteor shower on the night of December 13–14, 1971, when the shower was at its peak.

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