Analysis of the 1984 Ivanovo tornado outbreak using the WRF-ARW model

The Ivanovo tornado outbreak on 9 June 1984 is one of the most destructive in the history of instrumental observations in the USSR and Russia. According to different data, at least eight convective storms led to the formation of eight to thirteen tornadoes that day, although this number may be underestimated. This study presents an analysis of the Ivanovo tornado outbreak using simulations with the non-hydrostatic mesoscale model WRF-ARW with several nested grids, the innermost of which have a resolution of 1 and 3 km, in convection-permitting mode. The ability of the model to simulate convective events was evaluated in comparison with satellite and ground-based observations.

It was found that the 3 km resolution model reliably reproduced the observed convective storms of the outbreak, including the supercells. The closer the cells were located to the centre of the cyclone’s occlusion, the more accurately the model reproduced their characteristics. By analyzing updraft helicity, it was confirmed the presence of at least four mesocyclones, which resulted in formation of tornadoes identified earlier from satellite data on windthrow and by eyewitness observations. The higher-resolution mode (1 km) enabled some of the characteristics of the analysed storms to be specified. In particular, supercell merging and a kind of ‘the Fujiwhara effect’ were identified. Characteristic signatures were detected in areas where particularly large tornadoes occurred. The process of rear flank downdraft occlusion and tornado genesis in the Ivanovo supercell was analysed. It has been suggested that an anticyclonic tornado occurred alongside the main F4 tornado that passed through Ivanovo.

The study was supported by the Russian Science Foundation (grant no 24-17-00357).