Sky radiation, polarization and twilight radiation in Greenland

Summary

• A) The measurements of the spectral radiances in the solar almucantar (scattering function) and the degree of polarization of the skylight in Greenland indicate the following: 1) The air near the surface of the ice cap of Northern Greenland is very pure. 2) The sky radiance however is different from the pure molecular (Rayleigh) atmosphere, the measured scattering function does not followRayleigh's law. 3) On the other hand the measured scattering functions cannot be explained satisfactoryly by scattering on the aerosols which have been measured near the surface. 4) Therefore the presence of a few particles per cm³ with radii in the range 0.10≤r≤1μ in heigher atmospheric layers has to be postulated.

• B) The measured twilight radiances give information on the vertical distribution of the aerosol concentration. The results show a lack of particles near the ice cap surface. The vertical increase of the particle number has a maximum at heights between 4 and 8 km. The profile above these heights is the same as in mid-latitudes.