Articles | Volume 22, issue 11
Ann. Geophys., 22, 3971–3982, 2004

Special issue: 10th International Workshop on Technical and Scientific Aspects...

Ann. Geophys., 22, 3971–3982, 2004

  29 Nov 2004

29 Nov 2004

Combined wind profiler-weather radar observations of orographic rainband around Kyushu, Japan in the Baiu season

Y. Umemoto1, M. Teshiba1, Y. Shibagaki2, H. Hashiguchi1, M. D. Yamanaka3,4, S. Fukao1, X-BAIU-99, and X-BAIU-02 observational groups5 Y. Umemoto et al.
  • 1Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611–0011, Japan
  • 2Osaka Electro-Communication University, Neyagawa, Osaka 572–8530, Japan
  • 3Graduate School of Science and Technology, Kobe University, Kobe 657–8501, Japan
  • 4Inst. of Observ. Res. for Global Change, Japan Agency for Marine-Earth Science and Techn., Yokohama 236–0001, Japan
  • 5Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki 305–0052, Japan

Abstract. A special observation campaign (X-BAIU), using various instruments (wind profilers, C-band weather radars, X-band Doppler radars, rawinsondes, etc.), was carried out in Kyushu (western Japan) during the Baiu season, from 1998 to 2002. In the X-BAIU-99 and -02 observations, a line-shaped orographic rainband extending northeastward from the Koshikijima Islands appeared in the low-level strong wind with warm-moist airs. The weather radar observation indicated that the rainband was maintained for 11h. The maximum length and width of the rainband observed in 1999 was ~200km and ~20km, respectively. The rainband observed in 2002 was not so developed compared with the case in 1999. The Froude number averaged from sea level to the top of the Koshikijima Islands (~600m) was large (>1), and the lifting condensation level was below the tops of the Koshikijima Islands. Thus, it is suggested that the clouds organizing the rainband are formed by the triggering of the mountains on the airflow passing over them. The vertical profile of horizontal wind in/around the rainband was investigated in the wind profiler observations. In the downdraft region 60km from the Koshikijima Islands, strong wind and its clockwise rotation with increasing height was observed below 3km altitude. In addition, a strong wind component perpendicular to the rainband was observed when the rainband was well developed. These wind behaviors were related to the evolution of the rainband.