Dynamics of a Relative Long Positive Streamer from an Isolated Hydrometeor

Abstract:

Streamer discharges appear in many natural phenomena [Bazelyan and Raizer, 1998, 2000]. They are known to play important roles in the initiation and propagation of lightning [Rakov and Uman, 2003]. A few recent studies have investigated the initiation of streamers from hydrometeors under thundercloud electric field conditions in order to understand the initiation process of lightning [e.g., Liu et al., Phys. Rev. Lett., 109 (2), 025002, 2012; Petersen et al., Q. J. R. Meteorol. Soc., 141, 1283, 2014; Sadighi et al., J. Geophys. Res., 120, 3660, 2015]. But the properties of long streamers initiated from isolated hydrometeors are poorly understood. A recent observation [Rison et al., AGU Abstract AE22A-02, 2014] reported the initiation of lightning discharges began with electric breakdown waves that propagated through 500-900 m with speeds of 3-5×10⁷m/s and suggested these were positive streamers.

In the presentation, we will report a modeling study on the dynamics of a relatively long positive streamer (~4 cm) initiated from an isolated hydrometeor in a background electric field with a reasonable magnitude. The modeling results indicate while the streamer shows a generally exponential growth feature, its characteristics such as channel radius, electron density, and current density exhibit collocated fluctuations. The exponential growth property allows us to use the modeling results to predict the characteristics of longer streamers, and to quantify the thunderstorm electrical conditions including the high-field region size and potential difference in order to accelerate the streamer to the high speed of the initial breakdown waves of lightning observed by Rison et al. [2014]. It is found that the streamer radiates in the high frequency and very high frequency region of the electromagnetic spectrum. A potential difference of 0.3-1.8 MV is required to accelerate it to the high speed of 1-5×10⁷ m/s.