The efficacy of subsidence warming in the core of numerically simulated tornado-like vortices

Vigorous downdrafts are known to occur in tornadoes, as shown in numerous observational, laboratory, and modeling studies. Few of these studies document the potential impact of subsidence warming in the vortex core on the central pressure deficit and subsequent maximum wind speeds attained by tornadoes. These studies are inconclusive on the efficiency of such warming in contributing to the pressure deficit. The purpose of this study is to provide quantitative bounds on the efficacy of subsidence warming in idealized, tornado-like vortices.

An axisymmetric numerical model of the incompressible primitive equations of motion is utilized to investigate the subsidence warming contribution to the central pressure deficit and subsequent maximum wind speeds over a range of physical conditions. A liberal parameterization is used in an attempt to get the maximum possible effect. Sensitivity and resolution experiments are conducted to verify the robustness of the model and the accuracy of the results.

Over 90 simulations are run, varying viscosity, background circulation (the “coriolis parameter”), and the strength of the warming (“advective buoyancy”). Statistical analysis of the results is performed to quantify the impact of warming in the core on the pressure deficit and maximum wind speeds. Under optimal conditions, subsidence warming only increases the pressure deficit by a maximum of about 30%. There is no significant impact on the maximum wind speeds, and thus subsidence warming is not a valid explanation for wind speeds in tornadoes exceeding the thermodynamic speed limit.