11:30 AM - 11:45 AM
[AAS13-10] Phased Array Weather Radar Observations of Mesocyclone Structures in Okinawa
Keywords:Phased Array Weather Radar, Mesocyclone, Three-dimensional Structure
In the afternoon, December 6, 2016, a linear rainfall band accompanied by a stationary front passed over the Okinawa main Island. The rainfall band was composed of some echo cells, which moved from SW to NE along the band direction. A kink echo was found on the CAPPI at 1 km height on 15:29 JST. It changed into a vortex echo, which diameter is 3 to 5 km, on 15:34, and maintained the vortex structure up to around 15:38. The distribution of Doppler velocity showed the two eyes of maximum and minimum of velocity that indicates Rankine's vortex. This feature indicates a mesocyclone (MC) existence. From the maximum and minimum velocities of +17 m/s and -20 m/s, respectively, and the diameter of 3 km, the vorticity of 0.025 s-1 is calculated. The MC appeared between 0.25 km and 1.75 km in height, and convergence flow in the lower layer and divergence flows in the upper layers were found. Another stronger MC was found at between 4.0 and 5.0 km in height, which was accompanied by a precipitation core in the upper levels. The echo top height was over 12 km, and anvil echoes extended to the backward (NW) of the linear rain band.
The MC was also observed by C-band polarimetric radar (COBRA), it is possible more advanced data analysis such as dual-Doppler. Although the observed MC has a large vorticity, which is able to generate tornadoes, there are no structures of supercell and there is no evidence of tornado occurrence. From the first kink echo and the next vortex echo may indicate the horizontal wind shear. It seems that the MC has the similarity of the vortex echo appeared in the winter monsoon reported by Fujiyoshi, 2001 (Tenki). However, we have to investigate more carefully about the cause of the upper level MC.