Observational Study on Medium-Scale and Tropical Cyclones in the Subtropical frontal zone

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The objective of this project is to study structure and dynamics of the medium-scale extratropical cyclones (appeared in the subtropical front zone near Japan during Baiu and Shurin seasons) and the tropical cyclones, based on observations by the MU,boundary-layr and meteorological radars. The major results of this project are as follows :1.Baiu-and Shrin-frontal medium-scale extratropical cyclonesThe standard observations by the MU radar since 1986 have been reviewed. In particular, the MU radar data obtained by a three-week Baiu observation campaign carried out during 17 June-8 August 1991, as well as those obtained by meteorological radars (X-, C-and Ku bands), radiosondes, meteorological satellites (GMS) and objective analyzes by the Japan Meteorological Agency (JMA), have been studies in detail. An asymmetric structure of the medium-scale cyclone and a hierarchical structure of cloud clusters have been found out. Variations of the tropopausal jet stream, lower-stratospheric inerti … More o-gravity waves and turbulence (eddy diffusivity, etc.) have been also studied.2.Typhoons and their modification processes Two strong typhoons (T9019 on 19-20 September 1990, and T9426 on 29-30 September 1994) passed in the vicinity of the MU radar observatory have been studied in detail. Combining the MU radar data and the JMA storm-track calculations, the tangential and radial wind fields have been analyzed as a function of altitude and radial distance from the typhoon center. Typical axi-symmetric structure appeared before the center passage, whereas asymmetry and transformation into extratropical cyclone were strongly suggested after the center passage. In particular, for T9426 of which the center passed almost over the MU radar observatory, distributions of angular momentum, vorticity and helicity have been analyzed. Conbining these results and the data of surface weather, meteorological radars, rawinsondes, GMS and a boundary-layr radar (at Sakai Electric Power Plant), detailed information on the structure of the typhoon center (eye) have been obtained. The typical warm-core structure has been confirmed, and a spiral structure (similar to a tornade) has been found out. The latter was seen as a local anti-cyclonic rotation in the tangential-wind analyzes.In addition to the scientific results mentioned above, the utility and data analysis method of the VHF/UHF radars for the mesoscale meteorology have been established through this project. Less