Features of anticyclonic tornadoes in a complex orography based on numerical simulations

Tornadoes are common atmospheric phenomena worldwide; however, the mechanisms governing non-supercell tornadoes, particularly anticyclonic ones, remain less well understood, especially in regions with complex terrain. In Mexico, a considerable number of non-supercell tornadoes exhibit clockwise rotation, and some studies suggest a potential link between topography and these phenomena. In this context, this study investigates two anticyclonic non-supercell tornadoes that occurred in central Mexico: one in Tlaxcala (2016) and another in Querétaro (2017) states, both within the Trans-Mexican Volcanic Belt. Using high-resolution simulations with the Weather Research and Forecasting model, complemented by satellite and reanalysis data, we analyze the environments that favored the development of these events. Both cases occurred under moderate instability, with weak to moderate wind shear and marked moisture flux convergence, modulated by orographic features. Results of model simulations show that mountain-induced perturbations generated alternating cyclonic and anticyclonic vertical vorticity fields along low-level convergence lines. The advection of negative vertical vorticity, coupled with vertical motion associated with convective updrafts, favored the initiation of anticyclonic rotation. Therefore, a schematic conceptual model is proposed to describe this process, emphasizing the key role of wind-orography interactions in producing surface vertical vorticity dipoles that may later evolve into non-supercell tornadoes. These findings underscore the importance of accounting for topographic influences in evaluating tornadic potential in complex terrains, providing a framework for understanding the relatively high frequency of anticyclonic vortices in regions with complex orography. • Terrain-wind interaction generated both, cyclonic and anticyclonic vorticity in central Mexico. • Moderate instability and a low-level shear environment favored the formation of non-supercell tornadoes. • WRF simulations linked terrain-induced vorticity to tornadogenesis mechanisms and spin direction of vortices.