Concentration and nature of ice nuclei in rim of the North Pacific Ocean

Abstract

Simultaneous collections of ice nuclei in the air were made with instruments of the same type at four sites in the rim of the North Pacific: College, Alaska; Blue Glacier, Washington; Mauna Loa, Hawaii; and Nagoya, Japan. Ice nuclei were collected on filter paper for counting of their number and also sheet meshes for examination with electron microscope.

During the period of the collection from the beginning of February through the beginning of March, 1968, three marked maxima of the concentrations of ice nuclei effective at ?15°C appeared at each of the sites except Mauna Loa. The peak values were the largest at Nagoya (5.3 nuclei/litre) followed by College (2.7 nuclei/litre) and Blue Glacier (1.3 nuclei/litre). At the Mauna Loa Observatory, no marked peak was observed. Neither a diurnal variation nor any other variations with a specific period have been detected. The result of identification of materials of ice nuclei collected at the four sites shows that clay and other mineral particles constitute the main part of the ice nuclei.

The results of the studies on the features of ice nucleus concentration, the trajectories of air masses and the examination of ice nuclei suggest that the ice nuclei detected originated from arid and semi-arid regions of the Asian Continent.