Possible stretching mechanisms producing the tornado vortex in the mid-level

We have developed a method to physically estimate the maximum tangential velocity, the diameter, and the rotation period of a tornado that could be generated under a specified atmospheric condition. Using this method, we can calculate them in each grid point from a numerical model output and utilize them as tornado forecast parameters such as EHI and STPC. The validation results using damage survey data for past tornadic events in Japan suggest that our method estimates correct F-scales for 76% tornadic events.

In our method, a calculation of vortex stretching in the mid-level is needed using a 1D vertical convection model. We will show the validity of the 1D vertical convection model by comparing it with some published materials and radar data. Our model does not reflect storm-scale atmospheric condition, and therefore is not so realistic as recent numerical simulations. However, our model reconstructed some features of tornadoes and storms such as hook echoes. Our validation did not show any evident discrepancies with compared materials. This result supports the validity of our 1D model and our new tornado forecast parameters.