Initiation of Streamers Due to Hydrometeor Collisions in Thunderclouds

Abstract

In order to initiate streamers and leaders under thunderstorm conditions the electric field should reach values higher than the critical breakdown field Ek (i.e., ∼30 kV·cm−1·atm−1). However, the maximum electric field in thunderstorms measured by balloons is ∼6–9 kV·cm−1·atm−1. In present work, to achieve the electric field amplification required for streamer initiation, a system of two approaching spherical hydrometeors is investigated. Streamer initiation is determined from a Meek number, describing electron multiplication in fields above Ek. We have found the relationships between radii of particles for successful streamer initiation in the gap between these two particles and also on the outside periphery of the two particle system when the particles are connected by a discharge channel. Furthermore, we estimated the frequency of streamer initiation using three realistic hydrometeor size model distributions available in the literature and found that the scenario of streamer initiation on the outside periphery is only possible for relatively high electric fields ≥0.5Ek at altitudes of 3 and 6 km.

Modeling of Streamer Ignition and Propagation in the System of Two Approaching Hydrometeors

“…Cai et al () determined that the optimum geometry for a streamer ignition at air neutral density and ambient electric field is and . We focus on this geometry, and we explore the ignition threshold as a function of decreasing separation.…”

“…The motivation of present work is to improve the understanding of the discharge dynamics in a system of two conducting hydrometeors. We complement the robust parametric study of streamer ignition for various conducting hydrometeor sizes and ambient electric fields reported by Cai et al (). We note that conducting hydrometeors is a model representation better suitable for liquid particles rather than ice particles.…”

“…Cai et al (2018) extended this study for two hydrometeors with different dimensions. Cai et al (2018) also evaluated the conditions for inception of streamers on the outside of the electrically connected hydrometeors. It is important to note that neither of above mentioned studies for two hydrometeors employed first-principles plasma fluid models, and all considered some form of approximate criterion for the corona and streamer ignition.…”

“…Cai et al (2017) performed modeling study of the electrical connection between two hydrometeors with the same dimension. Cai et al (2018) extended this study for two hydrometeors with different dimensions. Cai et al (2018) also evaluated the conditions for inception of streamers on the outside of the electrically connected hydrometeors.…”

“…We note that, although the model can handle arbitrary conductivity and permittivity, the present study is a follow-up to work of Cai et al (2018) and therefore studies the hydrometeors as perfectly conducting spheres. To achieve this goal, the conducting spheres are characterized by conductivity h = 1 S/m and relative permittivity r = 1.…”