Studies on Snow Crystals of Low Temperature Types and Arctic Aerosols ( The Second Expedition )

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For the accomplishment of the Field Research of the Monbusho International Scientific Research Program under the title of "Studies on the Snow Crystals of Low Temperature Types and Arctic Aerosols (The Second Expedition)", we carried out the field observations at Alta (69 56'N, 23 16'E) and Kautokeino (69 01'N, 23 03'E), Finnmarksvidda, Norway from December 23, 1987 to January 21,1988.Although the air temperature condition in the Scandinavia area was relatively higher than the normal value, the observations carried out at two sites were quite successful. Because, a number of snow crystals of low temperature types, especially "Gohei twin" and "Sea gull" types were observed during the observation periods when air temperatures changed from 5 C to -28 C at Alta, and from -1 C to -36 C at Kautokeino. Especially, the "Double gohei twin" type snow crystals were discovered under the relative warm temperature conditions at both sites.Based on a number of microphotographs taken in the polar regions and obtained in laboratory experiments, the correlation of crystal growth among the "Gohei twin", "Sea gull" and "Spearhead" type crystals was discussed. As a result, the formation mechanisms of "Gohei twin" and "Spearhead" type crystals were considered as a combination of a cubic structure model and a rotation twin on the basal face. Furthermore, it was considered that the sea salt nuclei contributed to the initiation of the polycrystallization of supercooled cloud droplets.