Electromagnetic and optical characteristics of lightning measured in the Earth's ionosphere

This dissertation is an experimental study of the upward coupling of lightning electromagnetic waves to the lower ionosphere which was investigated by a rocket flight over a very active thunderstorm near Wallops Island Virginia. The trajectory took the rocket over the thunderstorm to an altitude of 400 km. Along with electric and magnetic field measurements, simultaneous data were obtained from a host of ground instruments including a lightning 3-D mapping system called LDAR, the National Lightning Detection Network and ground optical flash data.; We look at optical flash data and compare cases which were simultaneously recorded by the rocket and ground optical instruments. The optical flashes show the difficulties of distinguishing in-cloud and cloud-to-ground lightning. In a second part of the optical study using the ground based optical measurements, no relation is found between the stroke brightness and the NLDN estimated peak current. The optical study should have important applications to the interpretation of satellite based lightning studies. We also show that the use of the measured rocket VLF electric fields can be used as an aid in distinguishing between cloud-to-ground and in-cloud lightning rocket measured optical flashes.; Lightning produced field aligned electric pulses, which had also been reported on previous rocket experiments, were measured up to 240 km altitudes. The nature of the pulse is carefully analyzed, and the conclusion is that the electric pulse is probably composed of large amplitude vertically polarized waves at higher frequencies which do not produce a unipolar electric field. The pulse is produced by cloud-to-ground strokes but generally not by intra-cloud lightning. This is because much larger vertical electric fields are produced by cloud-to-ground lightning stroke channels.; The electron density profile of the F region ionosphere is deduced from the dispersion of whistler waves measured by the rocket. The results compare very well with the on-board Plasma Probe instrument and ionosonde measurements taken in Bermuda at the time of flight. This is the first time that this method has been used in the lower ionosphere.; The correlation between the electric field of whistler waves in the ionosphere and the ground NLDN measured stroke current is computed for frequencies between 500 Hz to 20 kHz. We find that the highest correlation with NLDN estimated currents is at the lower frequencies. Based on this result and the previous work of Y. Li, [Li, 1993], it should be possible to estimate lightning stroke currents from an orbiting satellite.; In a collaborative effort with Professor Nagano at the Electrical Engineering Department at Kanazawa University, Japan, a new 3-D lightning simulation model is compared with measured data from the rocket. The model calculates the electromagnetic fields from lightning in the ionosphere. The computed wave fields are larger than the measured whistler wave amplitudes, but the model used an estimated ionospheric density. In a later study, we plan to update these results with the new ionosphere density profile estimated in this thesis.