a Model of the Lightning Return Stroke.
The electromagnetic fields radiated by a lightning return stroke provide a means of learning about the return stroke current by remote sensing techniques. This thesis deals with two models that are needed to establish the correspondence between the current and fields. One of the models allows, for the first time, predictions to be made of electromagnetic fields from a complex return stroke current model in a realistic earth -ionosphere environment. The effects of propagation on the electromagnetic fields have successfully masked sub -microsecond time scale behavior in the electromagnetic fields until very recently. The field model established in this thesis is used to establish the sensitivity of the fields to changes in ground conductivity, velocity of propagation of the current pulse on the return stroke channel and channel model geometry. The second model calculates the details of the development of the return stroke current in time. While treatment of all of the known physical processes is not possible with current computers this model successfully predicts the slowing of the current pulse along the channel and the increase in rise time with propagation along the channel. This non-linear model predicts, for the first time, the details of the radial behavior of the current pulse. The cooling of the channel prior to the arrival of the current pulse is successfully predicted as well as a shell structure in temperature for the channel after the current pulse has passed. This cooling requires that the hot channel left by the leader processes must be at least 4 cm in diameter as long as there is no continuing current.
- Pub Date:
- Physics: Atmospheric Science