Abstract
Observations of pre-activated ice nuclei were carried out at Barrow, Alaska, and at the summit of Mt. Fuji, 3776m above sea level, in winter. Outside airat subzero temperature was sampled simultaneously by two millipore filters of pore size 1.2&. One of the filters was developed by the usual method of using supercooled sugar solution for counting the number of ice nuclei, without warming it above 0°C. The other one of them was developed after warming above +20°C. Difference of number of ice nuclei between the cold filter and warmed one indicates the number of ice nuclei pre-activated by cooling. It was concluded from these observations that the pre-activation process by cooling occurs in polar air masses and in the upper atmosphere.
