Solar radiation extinction, sky radiation, sky light polarization and aerosol particle total number and size distribution on the Island Maui (Hawaii)

Summary

During April 1964 and from August through September 1965 measurements have been performed on the Maui Island, Hawaii. The results can be summarized as follows:

• a) the spectral extinction coefficient has a diurnal variation. The greatest value is found during noon. Its wavelength dependency shows an ‘anomalous extinction’, the maximum of extinction is to be found at 0.55 μ (Figures 1–3).

• b) the spectral radiance distribution of the total sky indicates the tendency that the aerosol size distribution does not follow a continuous power law. The exponent for small particles seems to bev ^*<4 (Figures 4–5). The distribution of the sky radiation is not symmetrically. Sometimes the minimum shifts out of sun's vertical. The theoretical values for a molecular atmosphere differ from the measured noticeable.

• c) the spectral sky radiance close to the sun results in an exponent of the aerosol size distributionv ^*=4 for particle radiir>1 μ (Figure 8).

• d) the distribution of spectral degree of sky light polarization shows two maxima of polarization situated out of sun's vertical. This indicates a haze layer in the upper atmosphere (Figures 12–14).

• e) the number of the Aitken-nuclei 1965 is more than 250 per cm³, thus higher than 1964. This can be explained by the unusually weak trade wind circulation during summer 1965. The directly measured aerosol size distribution of a volume of air on the Haleakala summit follows a power law only approximately with the exponentv ^*=3. On sea level it is between 2 and 3. It is smaller than that for the total atmosphere. On the summit particles in extreme dry air were found as droplets too (13.3.4).

• f) Finally some measurement results of radiances and degrees of polarization are given for radiation which is reflected from the clouds underneath the Haleakala summit and from other objects (Figures 23–26).