Interferometric Imaging of Lightning Initiation through LOFAR: Uncovering the Spontaneous and Not-So-Spontaneous Nature of Lightning Initiation in 3D

With recent advances in instrumentation and the continued development and refinement of analytical methods, the hindrances that previously existed in uncovering the physical processes governing the behavior of lightning are diminishing. The focus of this dissertation research, interferometric imaging of lightning initiation through beamforming via the Low Frequency Array (LOFAR), will describe in detail how both the instrumentation and methods cooperate to enable the detection of lightning processes in which are below the level of the galactic and thermal very high frequency (VHF) background on individual antennas within the array. These conditions have proven to be integral in uncovering of two novel methods of lightning initiation. For one event, a broad discharge is observed propagate with a velocity of 4.8 +/- 0.1 x 10^6 m/s while increasing in intensity from below the LOFAR noise level. For the second mode of initiation, a negative discharge was observed to propagate with a velocity of 1.5 x 10^3 m/s, which is three orders of magnitude slower than normal negative leaders. The first shares features with previously conceptualized ideas of how lightning initiates. This is supported by other researchers, but the findings have unique features that are not explained by the current theories how lightning initiates. Furthermore, the second initiation method is new and unlike any other known lightning process. Lastly, it should be noted that the results we present these use true 3D interferometric imaging techniques. Without the development and implementation of these methods the results reported within this work would not be possible. This thesis will briefly discuss the current understanding of lightning and related phenomena to give an overview the topic and context for why the study of lightning is important. This will the be followed by current theories of how lightning initiates, and then by discussion of the development of the 3D interferometric techniques and their implementation. Next, the thesis will present two recently observed processes by which lightning leaders form, after which is a discussion of the implications of these findings and how they are distinct from known lightning processes. Additionally, we will discuss results from the possible detection of gamma ray glows from the thunderstorm balloon campaign. These findings are the result of the updated methodology and instrumentation when this project was transferred to the University of New Hampshire from the Florida Institute of Technology. Lastly, the thesis concludes with a review of the implications of these discoveries and a discussion of future investigations, as well as, propose methods to further uncover additional details of the physical processes behind lightning initiation and where the results of the observations reported in this thesis fit within the current understanding of how lightning initiates