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

完成文部省国际科学研究计划的“低温型雪晶和北极气溶胶的研究”的野外研究（第二次考察）"，我们在阿尔塔进行了实地观察（69 56 'N，23 16' E）和Kautokeino（6901 'N，2303' E）的平均气温。虽然斯堪的纳维亚地区的气温状况比正常值偏高，在两个地点进行的观测相当成功。因为，在观测期间，当气温在阿尔塔从5摄氏度变化到-28摄氏度，在考图凯诺从-1摄氏度变化到-36摄氏度时，观测到了一些低温类型的雪晶，特别是“五平双胞胎”和“海鸥”类型的雪晶。特别是在两个地点相对温暖的温度条件下发现了“双五平双晶”型雪晶，根据在极地拍摄的大量显微照片和实验室实验结果，讨论了“五平双晶”、“海鸥”和“矛头”型雪晶生长的相关性。其结果是，“五平孪晶”和“矛头”型晶体的形成机制被认为是一个立方结构模型和旋转孪晶在基面上的组合。此外，还认为海盐核对过冷云滴多晶化的形成起了重要作用。

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.