Observational Investigation of a Tornadic HP Supercell Storm in Eastern China

In this paper, a detailed analysis on a tornadic HP supercell’s environmental conditions, structure and evolution is made based on the Doppler weather radar data, routine upper-air and surface observation, and intense automatic weather station observation. The main results are as following: 1) This HP supercell occurred in the moderate CAPE and significant 0-6 km vertical wind shear environment, with high value of low level (0-1 km) vertical wind shear and low LCL at same time. The moderate CAPE and significant 0-6 km vertical wind shear favors the generation of supercell, while the high value of low level (0-1km) vertical wind shear and low LCL favors the occurrence of strong tornadoes. 2) This HP supercell began to develop when the pre-exist long convective rainbelt widen and shorten, the mesocyclone first appeared in the middle cell of the rainbelt, beginning at 4km height and then developing upward and downward. Soon, another mesocyclone also develop in the southern cell of the rainbelt, and gradually the southern cell merged with the middle cell, forming a strong HP supercell, with a 12km diameter mesocyclone embedded. The vertical vorticity associated with the mesocyclone is 1.5×10^-2 s^-1. The radar echo of this supercell successively displayed kedney, spiral, “S” shape, and finally evolved into bow echo, lasting more than 2 hours. 3) The EF3 tornado occurred during the “S” shape period. Before tornado touching down, a TVS appeared in the central part of the large mesocyclone, corresponding to a vertical vorticity value of 6.0×10^-2 s^-1. When the tornodo was underway, strong divergence present at the storm top just above the tornado, with a divergent value of 0.8×10^-2 s^-1. The mesocyclone that lead to the tornado lasted 2 hours and 13 minutes. The mechanisms for mesocyclone generation and HP echo revolution are discussed in details.

Key Word: HP Supercell, Strong Tornado, “S” Shape Echo, Bow Echo, Doppler Weather Radar