Cosmic‐radio‐noise measurements at 18 Mc/s made in Hawaii during the period of November 1958 to December 1959 are reported. Diurnal attenuation curves are presented for the summer, winter, and equinoctial months that show a very pronounced resemblance to the F‐region critical frequency curves. It is shown that an important part of the total attenuation can be accounted for by an ionospheric window effect. The remaining attenuation is attributed to deviative absorption in the F region and nondeviative absorption in the D region. A nighttime component of attenuation is observed and it is suggested that this phenomenon is related to the cooling of the ionosphere. Finally, it is observed that on numerous occasions when the F‐region critical frequency exceeds the operating frequency, considerable flux continues to arrive at the antenna. It is suggested that this can be accounted for in terms of cosmic radio radiation trapped and propagated underneath the ionosphere. It is also possible that thermal radiation from the ionosphere plays a secondary role in this phenomenon.

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Nightglow 6300 A and electron density data from Maui, Hawaii, have been analyzed by using the formulas of the paper by Peterson, VanZandt, and Norton (referred to as part 1). The observed 6300 A emission is found to consist of two components. The primary component may vary considerably during the night, and its variations are explained satisfactorily by the chemical reactions discussed in part 1; these variations correspond to variations in the height, shape, and magnitude of the electron density profile. The secondary, or background, component does not seem to vary rapidly during the night but may vary considerably from one night to another. The source of the background component is unknown. It is shown that the magnitude deduced for it is insensitive to errors in the many parameters that enter the calculations. Finally, even though the theory given in part 1 does satisfactorily explain the observations, the pertinent chemical reactions seem to be inefficient in producing the 6300 A nightglow.

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