Preventing Tornadogenesis—Concept for Thunderstorm Intervention

Throughout history, mankind has sought to minimize the impact of the unpredictability and severity of violent storms such as tornadoes. To date, solutions have focused early warning and on development of fortified buildings made to withstand the strong forces that are the hallmark of these atmospheric events. Sophisticated prediction methods have been developed to warn populations of potential storm danger. These "warn and seek shelter" mechanisms have clearly reduced the loss of life and, to a lesser extent, property damage associated with these natural events. However, despite our best efforts, loss of life and costly property damage are still strongly associated with severe weather phenomenon. This paper will describe a concept that may mitigate effects of these violent weather systems. By using beams of electromagnetic radiation from satellites or the ground to heat the fine structure of a mesocyclone, the formation of tornadoes may be disrupted. The objective is to prevent concentration of storm energy in tornadoes and diffuse it over a larger area. The anticipated result is minimum impact on overall weather without the death and destruction from tornadoes. Tornadogenesis, the process of tornado formation, is not well understood. There is a complex interaction of the relative motions within the storm. The shear interface between updrafts and downdrafts acts to concentrate energy in one or more tornadoes. The fact that most mesocyclones do not generate tornadoes is the basis for speculation that the injection of a small amount of energy can disrupt tornadogenesis in the at-risk storms. Doppler radar on the ground and in space must identify the precursors to tornado formation and direct the energy beam into the critical convective flow field.

Research on concentration of energy in the vortex of a tornado is a important to the capability to interact with a storm. Are there "Achilles' heel" zones that smooth the concentration of energy when stimulated with low levels of energy? Determination of the effect of external energy input in disrupting the convective flows is the key to the "taming" tornadoes and must be accurately simulated.

The concept was evaluated in 2000 using a numerical simulation with the Advanced Regional Prediction System Code at the Center for Analysis and Prediction of Storms (CAPS). Heating of the cold rain down draft was subjected to a tenth of the reference solar power satellite. The down draft was eliminated in the simulation, demonstrating the potential to interact. Conditions critical to tornado formation were examined in the simulation. Limitations on the code's ability to predict tornadogenesis includes the lack of comprehensive micro-physical assumptions, i.e. rain drop size. The simulation has since been improved and can now show tornadogenesis. The potential interaction with microwave radiation heating has not yet been tried in the latest simulation. Other numerical simulations are being used for tornadogenesis studies and may be practical for further computer analysis of interaction.

Quicker and cheaper acquisition of sophisticated data on heating of the storms might be obtained with a land-based system. Modified emergency vehicles equipped with gyrotron-based microwave generators. These trucks would converge on the probable path of a mesocyclone and beam power into the cold rainy downdrafts. They could also be equipped with appropriate radiometers for tracking the heated regions. It is conceivable that this experimental system could actually be developed into an operating tornado mitigation system. Each truck would have two to three microwave generators at 10 MW each. Ten trucks near the same storm could give 1000 MW of heating beam. Weather modification by a ground-based system has certain advantages. Local control and monitoring are immediate and include visual assessment. Microwave beams are directed upward which does not require the degree of safety interlocks of the space-based system. The cost of the system should be considerably lower than the space system. On the other hand, storm chasers have a low probability of encountering tornadoes. It will require a complex operation to determine the storm structure and to position the transmitters. At a minimum, the ground-based system will have a role in validating the effect of selective heating on thunderstorm convection.

Annual loss of hundreds of lives and property damage in billions of dollars is the result of severe weather in the United States. Tornadoes and hurricanes are principal agents of this damage through the extreme winds in these mesocyclones. There are some theories that global warming phenomena will increase the frequency and intensity of these storms. The capability for providing warning of hazards from these storms has improved, but the capability to disrupt tornado formation should be developed.

To assess concept feasibility, more research is required, especially in the areas of numerical simulation and in beam propagation analysis. A program to pursue such goals must rest on firm public support in which the risks and benefits are clearly set forth.