沖縄本島横断時に楕円形へと変形した台風Saomai の眼の解析

Abstract

The eye of Typhoon Saomai (T0014), distorted into an elliptical shape during its passage over Okinawa Island on 12 Sep. 2000, is analyzed. The typhoon formed double concentric eyewall structure over this period, and it was the inner eye which deformed elliptical. After the deformation, it rotated almost three times with the fixed period of 3 hours from 15:30 JST to 23:30 JST. Then the typhoon lost such a distinctive structure after the entire eye and eyewall entered in the East China Sea. The time-space conversion of the surface meteorological data reveals essentially the same characteristics as what were seen in the other typhoons with elliptical eyes: i.e. the constant rotation rate, the negative pressure anomalies and enhanced rainfall at the longer axis side of the ellipse, etc. Meanwhile, a linear stability analysis based on the asymmetric balance model in log-pressure coordinates shows the wavenumber-2 instability, which theoretically supports the formation of the elliptical eye of typhoon Saomai. Keywords: Typhoon, Tropical cyclone, Elliptical eye, Elliptical eyewall, Asymmetric balance model