Non-precipitation echoes (NPEs) are often observed by C-band doppler radars in the vicinity of local front (e.g.: sea breeze front and gust front). In this presentation, we report on the correspondence of the NPEs observed in the vicinity of the local front and airflow structure associated with a localized heavy rainfall in Tokyo metropolitan area.
Dense observation project named TOMACS (Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities) has been conducted to understand the processes and mechanisms of extreme weather in the summers from 2010. TOMACS targets deep convections, which cause localized heavy rainfall in urban areas. Many types of deep convection are generated in the warm season in the Tokyo Metropolitan area, which is situated in a coastal region. Sea breeze fronts and gust fronts from other convections are one of the triggers of deep convection in Tokyo area (Kanto Plain). In clear sunny days, entering of NPEs from coastal areas toward inlands is sometimes observed by a C-band doppler radar network of the Japan Meteorological Agency. They are known to be visualized by scatterers such as insects and their locations are generally corresponded to those of local fronts. However, it is not known the exact relationship of spatial distribution of NPEs to airflow structure. In the observation of TOMACS on 23 July 2013, the analysis of the precipitation intensity data from dopplar radar and dopplar velocity, S/N ratio data from Doppler lidar revealed that the vertical distributions of NPEs were consistent with the height of the upper surface of the sea breeze flowing toward the inland. At first, NPEs scattered around the coast and then gradually converged to the edge of a sea breeze front. NPEs were also observed in the vicinity of a gust front. At first, the NPEs were several kilometers apart from a gust front head observed by a dopplar lidar and then exhibited a gradual approaching to the edge of the gust front.