[A-AS04] 大気の鉛直運動を基軸とした地球環境学の新展開

[AAS04-02] Vertical air motion and precipitation processes in shallow-type heavy rainfall

★Invited Papers

*重 尚一¹、戸田 望¹、青梨 和正¹、後藤 悠介²、篠田 太郎²、橋口 浩之³ (1.京都大学大学院理学研究科、2.名古屋大学宇宙地球環境研究所、3.京都大学生存圏研究所)

キーワード：大気鉛直流、豪雨、MUレーダー

It was thought that heavy rainfall was caused by deep cumulonimbus clouds with radar echoes extending to the tropopause. However, recent satellite-borne radar observations have revealed that shallow cumulonimbus clouds with radar echoes far below the tropopause can cause heavy rainfall in humid atmospheric environments. This shallow type of heavy rainfall is extremely difficult to estimate from satellite-borne microwave radiometers, especially over land, because of weak ice scattering signatures. It has been speculated that collision and coalescence of water droplets below the freezing level (“warm rain” process) is important in the shallow-type heavy rainfall, rather than the ice process. However, the vertical motion of shallow-type heavy rainfall during the rainy season in Japan, successfully observed by a 50 MHz atmospheric radar (MU radar) at the same time as the precipitation radar and microwave radiometer onboard the GPM core-satellite, showed strong upward motion just above the freezing level rather than below. Furthermore, vertically pointing observations by meteorological polarimetric Doppler radar indicated the freezing of raindrops lifted by updrafts, suggesting that mixed-phase microphysical processes are responsible for this type of heavy rainfall.