Estimation of the Tangential Winds and Asymmetric Structures in Typhoon
Inner Core Region Using Himawari-8
Observations of the winds in tropical cyclones are still limited. We
propose a new method for deriving the tangential winds in tropical
cyclones, which employs a spectral analysis of high-frequency cloud
imaging by latest-generation geostationary meteorological satellites
such as Himawari-8. The method was applied to the visible images of
boundary layer clouds in the eye of Typhoon Lan (2017) over an 8.5-hour
period. The low-level tangential winds over the central two-thirds of
the eye in radius were close to a rigid body rotation and increased with
time. On its outside was a region with striating clouds rotating at much
higher angular velocities, which may have been super-gradient.
Asymmetric motions were visualized as the deviation from the inner
rotation, and the vorticity of some mesovortices were quantified. These
asymmetric motions are suggested to transport angular momentum to
accelerate the inner rotation.