Radar and in situ observations in a winter bow echo and associated mesovortices over the Japan Sea area

Winter tornadic storms over the Japan Sea area have been observed during the Shonai Area Railroad Weather Project between 2007 and present. While the wind and reflectivity structures of tornadoes have been already extensively studied by remote sensing techniques, near-surface in situ measurements have to be performed primarily with surface-based instrumentations (e.g., anemometers). In order to characterize winter tornadic storms near the surface, we have installed 26 weather transmitters (WXT520; Vaisala) at intervals of 4 kilometers in the area around the Shonai plain. Each device was been mounted on the top of a steel pole as high as 5 meters. The observation intervals are 1 second for wind direction and wind speed, and 10 seconds for temperature, humidity and pressure. The PPI observations at low elevation angle from the X-band Doppler radar at 30-s intervals, as well as near-surface in situ measurements with high temporal resolutions provided unique dataset to analyze detailed tornado structures. In this presentation, we will introduce radar and in-situ measurement in a winter bow echo on January 24 2008. The major features of the winter bow echo are as follows. 1) Radar high temporal observations (at 30-s interval) at low elevation angle reveal clearly the transition from the bow shaped echo to comma-shaped echo. 2) Doppler wind fields confirm that the strong rear-inflow jet (RIJ) existed at the bow apex. Several mesovortices and also observed along the leading edge of the bow. 3) The region of the bow apex was passed over the surface station in the study area and in situ measurement data for the RIJ eternalized. Furthermore, in situ measurement data for a mesovortex embedded in the bow echo were obtained and analyzed simultaneously.