Speaker
Description
During a lightning flash there are a multitude of propagating plasma channels, called leaders, that grow through the thunderstorm. After their growth these channels cool and lose ionization and conductivity. After hundreds of milliseconds these channels exhibit current pulses that then propagate along the leader plasma channels and re-heat them. These pulses are called dart leaders due to their fast propagation speed (~10^7 m/s). The physics of these dart leaders, how they get started and how they propagate, is not understood. In this work we image the beginnings of lightning dart leaders with the LOFAR radio telescope in order to try and understand how they start. We have found that each dart leader is unique, which makes for an interesting challenge to find the underlying physics. Some dart leaders are preceded by other small discharges of different types, while others seem to start out of the blue. Some dart leaders exhibit an exponential rise in radio intensity at their beginning, and others do not. After initiating, every dart leader shows strong fluctuations in radio intensity that could be due to poisson fluctuations in radio emitters, longer time-scale fluctuations in the plasma physics (i.e. pulsing), or perhaps even due to structure in the underlying lightning channel. It is a challenge to separate these three mechanisms. In this talk we will present LOFAR images of lightning dart leaders, with explanations of what we see, and possible explanations of our data.
