Mammatus‐Like Echo Structures Along the Base of Upper‐Tropospheric Outflow‐Layer Clouds of Typhoons Observed by Cloud Radar

• Published in: Geophysical research letters 2021-10, Vol.48 (19), p.n/a
• Main Authors: Ohigashi, Tadayasu, Tsuboki, Kazuhisa, Shinoda, Taro, Minda, Haruya, Kyushima, Moeto, Yamada, Hiroyuki, Iwai, Hironori
• Format: Article
• Language: English
• Subjects: cloud radar; mammatus; outflow‐layer clouds; turbulence; typhoon
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094973

Upper‐tropospheric clouds in the outflow layer of typhoons can affect the track of typhoons (tropical cyclones) through radiation effects. In this study, the microstructure of the outflow‐layer clouds of several typhoons was examined. Cloud radar observations of three typhoons around Japan revealed numerous protuberances in echoes along the base of the upper‐level clouds, which are referred to as mammatus‐like echoes. The horizontal and vertical scales of these mammatus‐like echoes were 0.5–3.0  and 0.3–1.5 km, respectively. Vertical observations revealed downward (upward) Doppler velocities in (between) the hanging echo regions. Upward and downward velocity maxima were estimated at 3 m s−1 around the mammatus‐like echoes. Neutral stratification developed in the dry layer beneath the cloud base in which the mammatus‐like echoes formed. These mammatus‐like structures may promote mixing along the cloud base that contributes to dissipation of the outflow‐layer clouds. Plain Language Summary Heating and cooling due to radiative effects associated with upper‐level clouds spreading from a typhoon have been reported to have an impact on the actual track of the typhoon. Therefore, it is important to clarify the processes of formation and dissipation of the upper‐level clouds of typhoons. However, observations of such clouds, which are formed from relatively small ice particles, are scarce and the process of their dissipation is not well understood. In this study, we used cloud radar, which can detect clouds formed of small ice particles, to observe the upper‐level clouds of three typhoons that approached Japan. At the base of the upper‐level clouds, we found many protuberance structures with 0.5–3.0 km width and 0.3–1.5 km depth. These protuberance structures were accompanied by relatively large vertical motions of approximately 3 m s−1. The temperature and water vapor distributions near the base of the upper‐level clouds of the studied typhoons were conducive to these vertical motions. The small‐scale protuberance structures might promote dissipation of upper‐level clouds along their base. Key Points Protuberances observed by cloud radar along the base of outflow‐layer clouds of typhoons are termed mammatus‐like echo structures The mammatus‐like echo structures are associated with vertical motions with velocity of several meters per second Mammatus‐like echoes occur in a layer with high potential for turbulence caused by sublimation of ice particles falling into