Abstract
It is observed that potential ice nuclei activated with the addition of iodine vapor to natural air, become highly active even at such a high temperature as -8°C.
Observa tions suggest that their concentration as well as that of natural ice nuclei increases exponentially along with the fall of activation temperature, although the former shows for steeper increase contrasted to the latter.
The size of these potential ice nuclei is several 10th micron or less, which is observed by electron microscope.
The Millipore filter is found to be much more useful than the cold chamber for comparative observations, but it appears to take in iodineactivated nuclei at less than -12°C, so due provisions have to be made for possible errors. The number of nuclei observed by means of the two methods is one order smaller for the filter method than for the cold chamber, this being ascribed probably to the nuclei of extreme small size.
In both Tokyo and Karuizawa, the variation of ice nuclei concen trations is very high on some days and very low on others, and differs considerably by day and by hour, indicating little difference between the two locations under different atmospheric conditions.
