Spiral vortex structure and energy spectrum in the Super Typhoon

This study aims to elucidate the detailed structure of Super Typhoon using numerical data generated by Cloud Resolving Storm Simulator (SFA0457). In typhoons, tube in core region (eye) is wrapped by spiralling vortex sheets (rain bands). In homogeneous turbulence (HT), similar spiral vortex was identified (Horiuti and Tamaki 2013), whose vorticity along the sheet is either parallel (Mode 1) or perpendicular (Mode 3) to the tube. Mode 1 and 3 induce -5/3 and −7/3 energy spectrum, respectively. In SFA0457, it is shown that vertical and horizontal vorticities dominate in the eye and rain band regions, respectively. Formation of this Mode 3 configuration is similar to HT. Stagnation flow caused by dual sheets converges to form recirculating flow, which stretches the sheets. Vortex tube is formed by axial straining and lowering of pressure. By differential rotation, neighboring vortex sheets such as rain front are entrained by tube and form spiral turns. The energy spectrum is extracted by scaling of velocity field induced by the tube. Azimuthal velocity obeys power-law of the distance from the center as u_θ ∼ r^{- -β} (Pirozzoli 2012). In SFA0457, β≈1/3 and the slope in energy spectrum is determined as (-3+2β=) -7/3, which is consistent with the spectrum induced by Mode 3 spiral vortex.