SEMINAR SERIES and COLLOQUIA

Two challenges in tornadogenesis research are discussed. The first identifies a possible role of the hook echo in tornadogenesis. Descending rain curtains in the hook echo might actively initiate tornadogenesis through downward transport of angular momentum, convergence of angular momentum at the surface, and subsequent creation of positive vertical vorticity beneath cloud base. This scenario is modeled in three-dimensions as a purely barotropic mechanism, and properties of the descending rain curtains are altered to investigate the effects on tornadogenesis of varying mixing ratios and rain curtain configurations. Resulting tornadoes are optimized for certain rain curtain mixing ratios and rain curtain configurations.

The second challenge discussed is nocturnal tornadogenesis. A comprehensive climatology of significant nocturnal tornadoes identifies shallow stable nocturnal boundary layers and low-level jets as hallmarks of these tornadoes. Low-level jets are associated with exceptionally strong low-level shear and storm-relative environmental helicity. The results suggest improvements to the recommendations of previous tornado climatologies, in the context of nocturnal tornado forecasting.

Additionally, the results of the significant nocturnal tornado climatology motivate a second set of simulations to test the effects of stable boundary layers on tornadogenesis that is triggered by descending rain curtains.
Increasing stability in the lowest kilometer is found to change the nature of inflow relative to environments with weaker or neutral low-level stability.

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