Real-time wind field retrieval system by using X-band radar network around Tokyo metropolitan area

In recent years, it has been pointed out that urban area implies a vulnerability to severe weather. Since weather surveillance radar is a suitable tool to monitor it, universities and research institutes have installed the radars for studying disaster mitigations; however they are operated individually for individual purpose. Now we are developing X-band radar network, which consists of such individual radars around Tokyo metropolitan area to watch a heavy rainfall and severe winds. The networking relieves an attenuation problem of X-band radar, and enables to estimate wind fields by using their Doppler velocity data. In this paper, we present the real-time wind field retrieval system by using the X-band radar network and its applications to estimate the wind information near the ground surface.

The wind field retrieval system consists of two parts: unaliasing and synthesis of Doppler velocities. As for the unaliasing, a dual-PRF method is now available in recent radar system; however our X-band radar network includes the radar in which the dual-PRF method is not available. At first, we compare the velocity data with the output of operational mesoscale model which is distributed by Japan Meteorological Agency every 3 hours. Then velocity data are unaliased by the assumptions of VAD, temporal continuity and spatial continuity step by step. This method were examined with the typhoon event, and showed the reliable performance.

The multiple Doppler velocity synthesis is based on a variational method which minimizes the cost function which is defined by a difference between observed and estimated velocities, mass continuity, and Laplacian of the estimated wind fields. The method assumes a logarithmic velocity profile as a bottom boundary condition, and the land use (roughness length) distributions are also considered. This assumption enables to estimate the wind speed near the ground surface, which is needed for the investigation of disaster mitigation. Then the estimated wind speeds are validated by the surface wind observations.