対流圏上層の偏西風蛇行から切り離されて形成される寒冷渦（切離低気圧）は、 下層の諸擾乱と相互作用し、 突風や大雨などの激甚気象を引き起こす要因となる。しかし、地表低気圧に比べ その気候学的特性や他現象 との関わりには未解明な点が多い。これまでの客観抽出法には、前段階であるト ラフの抽出や、広範な水平 スケール（半径約300-1000 km超）への対応に課題があり、寒冷渦のライフサイ クルの全容を解明するには 不十分であった。本研究では、寒冷渦の本質的な特徴であるジオポテンシャル高 度の凹みに着目し、その 形状を幾何学的に評価することで，トラフから連続的に追跡可能な寒冷渦抽出法 を開発した（Kasuga et al. 2021）。 本発表では、手法の詳細に加え、日本周辺における寒冷渦の統計的性質（Kasuga and Honda 2025）などの 応用例を紹介する。 Cutoff lows (cold vortices), which form by separating from meandering westerlies in the upper troposphere, interact with various lower-tropospheric disturbances and act as a factor to emanate severe weather events such as wind gusts and heavy rainfall. However, compared to surface cyclones, many aspects of their climatological characteristics and interactions with other phenomena remain poorly understood. Conventional objective detection methods have faced challenges in extracting the pre-existing troughs and accommodating a wide range of horizontal scales (ranging from approximately 300 to over 1000 km in radius), which has hindered a comprehensive understanding of the cold vortex lifecycle. In this study, focusing on the geopotential height depression that fundamentally characterizes cold vortices, we developed a detection method that enables seamless tracking starting from the trough stage by geometrically evaluating the shape of the depression (Kasuga et al. 2021) . This presentation describes the details of this methodology and introduces its applications, including the statistical properties of cold vortices around Japan (Kasuga and Honda 2025).

Antarctic landfast ice forms a stable extension of the continent and plays important roles in the Antarctic ecosystems, yet the drivers of its year-to-year variability remain poorly understood at the circumpolar scale. While previous studies have focused on individual regions, a unified understanding of what controls the annual minimum landfast ice extent has been lacking. In this seminar, I investigate the relative roles of local sea ice conditions and large-scale climate variability in shaping the circumpolar minimum landfast ice extent, which occurs in early March. Using satellite-derived sea ice area and major climate indices, I identify the key regions and timescales that provide predictive skill to a predictive model. The results show that variability of the annual minimum landfast ice extent is primarily driven by sea ice area in specific areas around Antarctica, while large-scale climate modes, particularly the Southern Annular Mode in September, act indirectly by modulating regional sea ice conditions rather than directly forcing landfast ice changes. The primary driver of landfast ice variability, sea ice area, is consistent around the coast, however the primary relevant climate modes to each sector varies. I will present a statistical framework that links these processes and demonstrates how commonly available climate variables can be used to estimate landfast ice extent outside of the observational record. Finally, I discuss the breakdown of this relationship after 2022, suggesting a recent shift in the dominant drivers of Antarctic landfast ice variability and raising important questions about future predictability in a changing climate.