InSAR observation and numerical modeling of the water vapor signal during 2008 Seino heavy rain Event, central Japan

This study reports the first detection and analysis of a localized water vapor distribution during Seino heavy rain episode by Interferometric Synthetic Aperture Radar (InSAR). The InSAR data retrieved during ALOS/PALSAR emergency observations for the event revealed a radar line-of-sight change of up to 130 mm within 10 km. Based on the signal, we estimated a three-dimensional water vapor distribution using the ray-tracing method, which indicated a column of nearly saturated water vapor within a 10 km² from the surface to 9000 m above ground level. To geophysically confirm this signal, Weather Research and Forecasting (WRF) model simulations were performed, and consequently suggesting the deep convection initiated by orographic lift of the Yoro Mountains 20 km south of the localized signal. On receiving results of WRF simulations, another simulation was performed without data of the Yoro Mountains, which did not reveal a deep convection. These results demonstrated the importance of realistic topography in the simulation of mesoscale convective systems.