S-band and X-band Radar Observation Characteristics of EF2 Tornado at Qingyuan of Baoding in 2021

Abstract

Using multiple observations such as S-band radar (SPOL) in Shijiazhuang, X-band phased array radar (XPAR) in Xiong'an, and ground-based encrypted automatic stations, detection features and evolutions of EF2 tornado at Donglü Village, Qingyuan District of Baoding City Hebei Province on 21 July 2021 are studied. The tornado occurred within the center of high dew point values and in an area characterized by a significant temperature gradient. There are convergence lines within the center of high dew point temperatures and a temperature gradient zone. From perspectives of environmental conditions such as convective available potential energy (CAPE), 0-6 km vertical wind shear, and the lifting condensation level (LCL), there is a possibility for tornado occurrence. It is evident that the tornado formed within a low-vortex precipitation cloud system, showing significant divergence at high altitudes. The subsequent storm propagation leads to multiple single-cell mergers and a supercell formation. A significant reflectivity factor core moving from southeast to northwest is observed at the top of hook echo, corresponding to the tornado location. Both SPOL and XPAR detected continuous mesocyclones on average radial velocity images, with dimensions ranging from 1.4 to 4.2 km, and rotating speeds of 10-20 m·s-1, indicating weak mesocyclones with short durations (30-35 min). During tornado development, a decrease in the lower angle detection of adjacent rotational speed pairs coincides with mesocyclone downward extension to 1.2-1.4 km and its diameter shrinking to 0.8-1 km, indicating tornado formation. Tornado storm parameters show maximum rotation speed and vorticity at low levels, promoting its intensification. Compared with XPAR storm parameters, SPOL features a larger maximum reflectivity factor (noless than 55 dBZ) and a greater distribution height (8-10 km). The consistency of SPOL and XPAR in detecting the tornado location, radial velocity, and storm diameter is compared. On the radar radial velocity image, there are pairs of positive and negative velocity values arranged symmetrically along the radial direction. The echo top of XPAR radar is approximately 6 km higher than that of SPOL radar, and the peak time of XPAR echo coincides with the storm's appearance. The tornado vortex signature (TVS) reaches its strongest period from 1536 BT to 1542 BT, extending vertically up to 2-4 km.

Keywords

• tornado
• storm characteristic parameters
• mesocyclone