5:15 PM - 7:15 PM
[AAS10-P10] Ground-based observation of snow particles in the windward / leeward areas of Uonuma Hills
★Invited Papers
Keywords:snowfall, cloud physics, topography
For the better understandings of snow growth processes depending on the topography, we conducted intensive snowfall observations at Tokamachi and Shiozawa, Niigata in the winter of 2023 and 2024, where is one of the heaviest snowfall areas in Japan. The 750m-high Uonuma Hills extended 30 km from north to south, separating the two observation sites by 12 km. We installed ground-based precipitation particle imaging sensors (called ground-based Rainscope). X-band polarimetric radars (FURUNO WR-2100) are also installed in Tokamachi and Shiozawa.
The ground-based Rainscope is modified for ground observation from Rainscope (Suzuki et al. 2023) which is a balloon-borne special radiosonde. Ground-based Rainscope allows precipitation particles to pass through a built-in infrared sensor, which triggers the camera's electronic shutter and records a still image of the particles. Particle falling velocity can be calculated from the time difference when the sensors above and below detect the particle and the distance between the sensors. Image analysis provides information on particle sizes such as long diameter, short diameter, circumference, and area, as well as shape information such as circularity and aspect ratio. In this study, for the comparison of snowfall between windward and leeward of Uonuma Hills, we assumed that the snow cloud that fell in Tokamachi (windward) crossed over Uonuma Hills and produced snow in Shiozawa (leeward) and estimated the travel time. There was a 10-15 minute travel time from Tokamachi to Shiozawa.
In cases of December 23, 2023 and December 23, 2024, in Tokamachi, graupel or graupel-like (rimed and lump-shaped) particles were dominant, on the other hand, large snowflakes (aggregates) with complicated shapes were mainly observed in Shiozawa. According to the horizontal and vertical cross-sectional structures of snow clouds observed with polarization radars installed in Tokamachi and Shiozawa, the strong radar reflectivity area that brought snowfall in Tokamachi extended over the Uonuma Hills and into the upper layers over Shiozawa. In addition, according to direct observation of precipitation particles in snow clouds using a balloon-borne Rainscope, launched at 17:31 (JST) on December 23, 2024, at Tokamachi, graupel-like particles were observed in the lower layer over Tokamachi and the upper layer beyond Uonuma Hills. Therefore, it was found that different types of snowfall processes exist at the two locations. On the windward side, graupel or graupel-like particles were formed by riming associated with updrafts in front of the Uonuma Hills. On the leeward side, graupel-like particles were formed by upper-layer supercooled droplets lifted by updrafts over the Uonuma Hills, and near the ground, snowflake formation was dominated by the aggregation of ice crystals without riming in the lower layers.
The ground-based Rainscope is modified for ground observation from Rainscope (Suzuki et al. 2023) which is a balloon-borne special radiosonde. Ground-based Rainscope allows precipitation particles to pass through a built-in infrared sensor, which triggers the camera's electronic shutter and records a still image of the particles. Particle falling velocity can be calculated from the time difference when the sensors above and below detect the particle and the distance between the sensors. Image analysis provides information on particle sizes such as long diameter, short diameter, circumference, and area, as well as shape information such as circularity and aspect ratio. In this study, for the comparison of snowfall between windward and leeward of Uonuma Hills, we assumed that the snow cloud that fell in Tokamachi (windward) crossed over Uonuma Hills and produced snow in Shiozawa (leeward) and estimated the travel time. There was a 10-15 minute travel time from Tokamachi to Shiozawa.
In cases of December 23, 2023 and December 23, 2024, in Tokamachi, graupel or graupel-like (rimed and lump-shaped) particles were dominant, on the other hand, large snowflakes (aggregates) with complicated shapes were mainly observed in Shiozawa. According to the horizontal and vertical cross-sectional structures of snow clouds observed with polarization radars installed in Tokamachi and Shiozawa, the strong radar reflectivity area that brought snowfall in Tokamachi extended over the Uonuma Hills and into the upper layers over Shiozawa. In addition, according to direct observation of precipitation particles in snow clouds using a balloon-borne Rainscope, launched at 17:31 (JST) on December 23, 2024, at Tokamachi, graupel-like particles were observed in the lower layer over Tokamachi and the upper layer beyond Uonuma Hills. Therefore, it was found that different types of snowfall processes exist at the two locations. On the windward side, graupel or graupel-like particles were formed by riming associated with updrafts in front of the Uonuma Hills. On the leeward side, graupel-like particles were formed by upper-layer supercooled droplets lifted by updrafts over the Uonuma Hills, and near the ground, snowflake formation was dominated by the aggregation of ice crystals without riming in the lower layers.