VHF emitting width and 3D polarization of lightning dart leaders

After the lightning initial stage, lightning flash plasma channels (leaders) can become unstable and exhibit current pulses called dart leaders that propagate back down the lightning channel. These pulses are difficult to understand as they are a type of dielectric breakdown on an already existing plasma channel. In this work we present VHF radio observations (30-80 MHz) of three dart leaders with the LOFAR radio telescope with meter and nanosecond level accuracy. We show that the radio emission comes from a meter-level (or smaller) width core. We also present the first 3D polarization data of dart leaders which shows that, at least sometimes, the VHF currents in dart leaders are parallel to the leader channel. Together, these observations reveal that the primary streamer activity in a dart leader comes from a very thin region and does not significantly involve the corona sheath that was originally established by streamers.