A Lagrangian view of moisture transport related to the heavy rainfall of
July 2020 in Japan: Importance of the moistening over the subtropical
The transport and accumulation of moisture played an essential role in
the extremely heavy rainfall of July 2020 in Japan. To better understand
this event in terms of moisture sources and transport routes, backward
particle trajectory analysis was conducted. We found two major moisture
sources: transport from the tropics and uptake from the subtropics. A
narrow moisture channel was found along the edge of the western Pacific
Subtropical High (WPSH), transporting the moisture to the Baiu front.
However, most moisture from the tropics was lost due to precipitation,
and their contributions were reduced to about 15%. In contrast, the
subtropical regions contributed over 80% moisture via evaporation and
lower tropospheric convection. Among those regions, the western Pacific
contributed the most (33 %). This study highlights the role of WPSH in
moisture transport, and also demonstrated the importance of the moisture
uptake during the transport.