Abstract
Observations of the number concentration of -20°C ice nuclei were carried out at Syowa Station (69°00'S, 39°35'E), Antarctica from the beginning of February 1968 to the end of January 1969. Especially, concerning the observation, special attention was paid to clarify the annual variation, the relation between meteor showers and the remarkable increases of ice nuclei and the effect of pre-activation of ice nuclei. Three different methods of the same two equipment were adopted, namely, the original, pre-heating and direct methods.
As a result, it was shown that the number concentration of -20°C ice nuclei increased in the winter season and decreased in the summer season in Antarctica. This means that the number concentration of ice nuclei increases when the observing station is under a condition of polar high pressure. As regards the relationship between meteor showers and the increases of ice nuclei, the relation was poor. Furthermore, it was expected that there were a number of minute ice particles and pre-activated ice nuclei which acted as ice nuclei in a broad sense in the free atmosphere in the winter season in Antarctica and the number concentration of these would be higher than those of natural ice nuclei in the cold regions.
