Quasi-Static Electric Field Signatures of Intra-Cloud Stepped Leaders

Abstract:

In [Pasko, GRL, 41, 179, 2014] modeling results using the electrostatic moment method solutions were used for quantitative interpretation of electric fields observed at close ~200 m [Winn et al., JGR, 116, D23115, 2011] and long ~30 km [Marshall et al., JGR, 118, 10907, 2013] ranges from intra-cloud (IC) stepped leaders. The modeling results reported in [Pasko, GRL, 41, 179, 2014] are consistent with the existence and continuous advancement of VHF-dark positive leaders at the positive end of the bi-directional leader system. It was demonstrated that the electric dipole moment of the entire leader system is a quadratic function of the leader length, and the dipole moment changes due to the leader steps increase proportionally to the overall leader length (i.e., even when step length remains constant), in good agreement with observations. In particular, the model time dynamics of the vertical electric field as would be observed on the ground at 30 km horizontal distance exhibited a progressive increase in electric field changes during steps of the negative leader, very similar to cases reported by Marshall et al. [2013]. We note that the data set reported in [Winn et al., 2011] in addition to the electric field components measured by balloon-borne electric field change instrument in the close vicinity to the IC leader, also contains a ground based electric field measurements. The purpose of this work is to conduct quantitative comparisons of the model results with these measurements. The obtained results and related analysis are supportive of the bi-directional leader ideas. We will present a comparison of model results obtained with and without advancement of the positive leader that indicate that the stalled positive leader model leads to unrealistic behavior of electric field components at close and long ranges from the IC leader when compared to observations.