Infrared scattering observations in the upper atmosphere

Observations of sky emission and absorption in the far infrared (mean wavelength 120 μ) and, simultaneously, sky emission at wavelength 6 μ have been made by P. Kuhn (ESSA) from the NASA CV-990 aircraft flying at 12-km altitude over the middle Pacific at latitudes 10°–15°N. A lack of correlation between the near- and far-infrared data, especially during times of visible cirrus cloud cover above the aircraft, indicates a wavelength-dependent atmospheric phenomenon, which is interpreted as scattering. The contributions of scattering by molecules, aerosols, water drops, and ice crystals in the upper atmosphere are estimated, and it is shown that the latter water drops and ice crystals may account for the observed phenomenon. The possible influence of scattering on past high-altitude solar observations is briefly discussed.