講演情報
[ACG68-P01]Localized formation characteristics of diamond dust investigated from field observations in Fairbanks, Alaska
大木 聡子1、*杉浦 幸之助2、堀 雅裕2、岩田 拓記3、植山 雅仁4 (1.富山大学大学院理工学研究科、2.富山大学学術研究部都市デザイン学系、3.信州大学学術研究院（理学系）、4.大阪公立大学大学院農学研究科)
キーワード：
ダイヤモンドダスト、野外観測、逆転層、アラスカ
Diamond dust is a limited snowfall phenomenon in which ice crystals sparkle in low temperatures, light winds, and clear skies. Although understanding of the basic conditions for diamond dust formation in nature has advanced, there is still scope for further study of its local characteristics and detailed formation mechanisms. In this study, we conducted field observations of diamond dust in Fairbanks, Alaska, USA, to understand the characteristics of the meteorological conditions at the time of occurrence and to investigate the possible sources of water vapor based on calculations of the sublimation time of ice particles. Furthermore, we compared our findings with previous studies in Hokkaido and considered the effects of regional differences on the conditions for diamond dust occurrence.
As a result of field observations conducted in Fairbanks, Alaska, USA, two cases of diamond dust were observed. A continuous decrease in temperature was confirmed from the night before the occurrence of diamond dust to the morning of the day of occurrence. Although it was not possible to identify the source of the diamond dust observed in this study, calculations of the growth time of ice particles suggested that ice crystals formed on the Chena River could be confirmed as diamond dust at the observation site. Furthermore, a comparison of diamond dust observations in Hokkaido from previous studies with those in Fairbanks showed that even at similar temperatures and relative humidity, the occurrence of diamond dust differed depending on the observation area. Although there were cases in Hokkaido where no temperature inversion was observed near the surface, a ground inversion layer was developed in all cases in Fairbanks. This suggests that water vapor supplied from the unfrozen Chena River formed diamond dust, which was then trapped near the ground surface by the ground-level inversion layer and drifted widely over a range of several kilometers. In the future, it will be important to quantitatively evaluate the role of inversion layers in the retention and diffusion of diamond dust by elucidating the relationship between the strength and duration of inversion layers and the frequency of diamond dust occurrence.
As a result of field observations conducted in Fairbanks, Alaska, USA, two cases of diamond dust were observed. A continuous decrease in temperature was confirmed from the night before the occurrence of diamond dust to the morning of the day of occurrence. Although it was not possible to identify the source of the diamond dust observed in this study, calculations of the growth time of ice particles suggested that ice crystals formed on the Chena River could be confirmed as diamond dust at the observation site. Furthermore, a comparison of diamond dust observations in Hokkaido from previous studies with those in Fairbanks showed that even at similar temperatures and relative humidity, the occurrence of diamond dust differed depending on the observation area. Although there were cases in Hokkaido where no temperature inversion was observed near the surface, a ground inversion layer was developed in all cases in Fairbanks. This suggests that water vapor supplied from the unfrozen Chena River formed diamond dust, which was then trapped near the ground surface by the ground-level inversion layer and drifted widely over a range of several kilometers. In the future, it will be important to quantitatively evaluate the role of inversion layers in the retention and diffusion of diamond dust by elucidating the relationship between the strength and duration of inversion layers and the frequency of diamond dust occurrence.