Abstract
A marked periodic oscillation of trochoidal motion was found in the track of the eye fixed by radar and satellite for the typhoon 8019 (WYNNE). Five remarkable oscillations with the period of 5hr-8 hr and the maximum amplitude of 23km were observed for 36 hrs by land-based Miyakojima radar. The amplitude decreased with decreasing period. The analysis of PPI echo image shows that the center of typhoon eye did not agree with the system center of the whole typhoon circulation; and the eye shifted and rotated counterclockwise around the system center.
In the occurrence of the phenomenon, the "double eye" structure of the echo and the double wind maxima were observed in the typhoon; the outer and inner eyewalls have diameters of about 260km and 30km, respectively. In particular, elliptical circulation of the pressure and wind fields and resulting the rectangular-shaped echo configuration were found an area inside the radius of the outer eyewall. The rectangle and elliptical circulation rotated counterclockwise around the system center with the same period of that of trochoidal motion. Both features were inscribed in the outer eyewall ring with radius of approximately 130km. The eye traced the subpoint corresponding to one of the focus of the ellipse on the major axis; consequently, the trochoidal motion took places in the typhoon circulation. However, it was not clear why the eye was shifted.
