Three‐Dimensional Structure of Cold‐Air Damming in the Kanto Plain, Japan, Revealed by Multiple‐Site Radiosonde Observations

ABSTRACT In winter, cold‐air damming (CAD) in Japan's Kanto Plain often results in snowfall, which can seriously affect infrastructure. This study investigated the three‐dimensional structure of CAD during a typical snowfall event on 4 March 2025 based on independently conducted simultaneous multiple‐site radiosonde observations, together with radiosonde observations from the Japan Meteorological Agency and surface observations. The observations revealed a distinct three‐layer structure: the inland cold air with a depth of 500–1000 m over the plain, an overrunning northeasterly to easterly flow, and warm air intruding from the south to southeast. This structure is consistent with the typical CAD observed east of the Appalachian Mountains of the eastern United States, which is characterised by warm air overrunning a cold‐air dome. An examination of the formation process further suggests that this CAD likely formed within a shallow low‐level layer owing to diabatic cooling associated with precipitation. This paper presents an observation‐based case study that documents the three‐dimensional structure of CAD, as well as an aspect of its temporal evolution over the relatively understudied Kanto Plain.