Formation of Hole Punch Clouds

Abstract Hole‐punch clouds (HPCs) are circular or oval cloudless holes in thin supercooled cloud layers. They are believed to be generated by aircraft passing through supercooled cloud layers; however, the exact formation mechanisms remain poorly understood due to the scarcity of observations. In addition, basic HPC formation characteristics, such as expansion speed, are controversial. Using geostationary meteorological satellite Himawari‐8 data and aircraft flight data of Flightradar24, this study clarifies HPC formation and development from 59 HPCs. Two growth stages of HPCs are identified: first, linear HPCs are formed. The length ( L major ) and width ( L minor ) of one of the long HPCs grew at rates of 43 m s −1 and 3.8 m s −1 . This occurs within 10–20 min of an aircraft passing through supercooled clouds and their orientations consistent with tracks of aircraft. The upward expansion speed of the HPC was approximately 1.2 m s −1 . Second, these linear HPCs expand slowly and homogeneously for over an hour. The growth rate modes of L major and L minor of all HPCs were both 1–2 m s −1 . All observed HPCs initially appeared as lines, thus supporting that HPCs are generated by aircraft. Sub‐grid‐scale cloud‐free areas or extremely thin supercooled cloud layers where aircraft passed would not generate HPCs. This is because not all aircraft that passed supercooled clouds generated HPCs.