Three-Dimensional Structure of Typhoon Mindulle (2016) and Near-Surface Streaks Observed By Phased Array Radar

Meteorological Research Institute has been operating an X-band phased array radar (PAR, hereafter) since 2015. The PAR performs high-speed volumetric scan every 10–30 seconds, by combining vertical digital beam forming technology and horizontal mechanical antenna rotation. It observes up to 60 km in range with a range resolution of 100 m and an azimuth resolution of 1.2 degree. On 22 August 2016, Typhoon Mindulle made landfall near Tateyama, Chiba and moved north across the Kanto Plain. We succeeded in observing a fine-scale three-dimensional structure of Mindulle as it passed close to the PAR observation site in Tsukuba, Ibaraki. The data obtained show that the inner region of Mindulle consisted of several spiral rainbands located around the center of circulating winds, in which many convection cells with typical 20-dBZ echo top altitudes of 5–8 km were embedded. We derived wind fields by carrying out a synthesis analysis of the Doppler velocity data obtained by the PAR and nearby operational radars. The low-level synthesis data show a strongly circulating wind region with a velocity of >25 ms^-1 which originally existed at several tens of kilometers from the center. The radius of the strong winds then monotonically decreased to <10 km in 20–30 minutes, implying a contraction of circulating winds presumably caused by a surface frictional force. The PAR reflectivity data exhibited rapidly developing convection cells in the innermost rainband, with 20-dBZ echo top altitude increasing from ~8 km to 14–16 km. This convection intensification was also detected by a meteorological satellite (Himawari-8) as a signature of brightness temperature lowering from 205 K to 199 K around the region in question. These results suggest a frictionally forced updraft occurring in the inner region of Mindulle during its decaying stage after landfall. In addition, the PAR Doppler velocity data exhibited signatures of numerous high-speed streak structures in the atmospheric boundary layer. The structures had a typical horizontal wavelength of 200–600 meters, consistently extending from ~40 meters to 300–600 meters above the ground level. In the presentation, we will discuss these observational features in conjunction with numerically-reproduced wind patterns caused by the boundary layer rolls associated with tropical cyclone.

[Acknowledgment] This work was supported by JSPS KAKENHI Grant Numbers JP15H03728 and JP17K13007.