Multiple radar observations and formation environment of a weak tornadic storm associated with a boundary layer convergent line
GUO Ruiling
BAI Lanqiang
CHAO Jinghua
YU Xiaoding
YU Xiaojian
LI Zhaoming
PANG Qiwen
Abstract：On the afternoon of 30 June 2022,an EF0 tornado struck Nanhai District,Foshan.Utilizing data from three X-band Doppler weather radars of distinct hardware standards,two additional S-band dual-polarization radars,surface meteorological stations,and atmospheric reanalysis products,the key multiple radar observational characteristics and the convective environment associated with this tornadic storm were systematically investigated.Results showed that no mid-level mesocyclone signatures were identified by any of the five radars,confirming this event as a non-mesocyclone tornado.Comparing with X-band radar observations,the S-band radars exhibited limited capability in detecting vortex signatures associated with the tornado and failed to identify tornado vortex signature(TVS).In contrast,the higher spatial-temporal resolution and enhanced low-level coverage of the X-band radars showed superior advantages in detecting such tornadic fine-scale structures.Comparisons of these X-band radars revealed that,the mechanical-scanning antennas,equipped with higher transmit power and narrower beamwidth,appeared to provide clearer features of TVS and weak-echo eye during this weak tornado.Although being advantageous in rapid scanning,it was relatively harder to capture such weak TVS features through the phased array X-band radars due to the lower transmit power and broader beamwidth.Further studies revealed that the tornado developed in a transition zone between the outer large-scale cyclonic circulation of Typhoon Chaba and the upper-level prevailing westerlies.Doppler products and surface wind observations suggested that the tornadic storm was triggered by the upward forcing along a convergence line within the boundary layer,and this tornado formed within a misocyclone approximately 4-6 km in diameter.Consequently,these findings infer that the near-surface mesocyclone,which was enhanced by the stretching of the pre-existing low-level ambient vertical vorticity,led to the non-mesocyclone tornado.
Keywords：non-mesocyclone tornadophased array radarconvergence linemisocyclonetropical cyclone
Publication Date：2025-06-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：14( 322-335 )