On an Asymmetric Wind Distribution in Typhoons: A Comparison of the Upper Wind Observed by the JMA Wind Profilers with the Gradient Wind

Abstract

For four intense typhoons having made landfall in the Kyushu District in the three years from 2004 to 2006,the radial pressure profiles are approximated objectively by the formulae presented by Schloemer, with the assumption that the isobars are expressed as concentric circles. Based on this profile, the gradient winds in the stationary pressure field are computed. The asymmetric property of the upper wind observed by WINDAS (WInd profiler Network and Data Acquisition System) of JMA are discussed in comparison with the gradient winds having axisymmetric distribution.
For the tangential component of the upper wind normalized by the gradient wind speed, the wind speed difference between the right and left directions against the typhoon translation increases with height, but the increase stops at 3350m height. So, the WINDAS wind at this level is analyzed,and it is shown that the wind difference is about twice of the translation speed.
The analysis of the crossing angle of the upper wind to the isobar indicates that outflow is outstanding in the front semicircle while inflow is prevailing in the rear semicircle. The large inflow angle is found in the left rear quadrant, while the large outflow angle is found in the left front quadrant. These angles are well corresponding to those between the circular isobars of the sea-level pressure and the vectors which are the sums of the translation velocities and the gradient winds.