On the mechanism of blue jet formation and propagation

Abstract

A new model of blue jets is proposed. A blue jet consists of an upward propagating leader whose top part is seen on photos as a “trunk of a tree”, and is capped at the top side of the leader by its streamer zone. The latter is shown as tall and narrow branches of “the tree”. It is shown that blue jet streamers can be sustained by relatively moderate cloud charges due to upward transfer of the high thundercloud potential by the leader. The streamer length is estimated along with the height at which the streamers can reach the ionosphere. The propagation of a streamer in the atmosphere of exponentially falling density N is computed. It is found that the critical external field ES required for unlimited streamer growth satisfies the similarity law ES/N ∼ const. Shortcomings of the existing blue jet models are discussed.

Dynamics of streamer‐to‐leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

“…The average electric field in a leader streamer zone is expected to reduce exponentially with altitude proportionally to air density, i.e., E cr = E cr,0 N amb /N 0 [e.g., Pasko, 2006, p. 266] (N amb can be approximately defined by the analytical expression N amb (h) = N 0 e -h/hN , with h N = 7.2 km and N 0 = 2.5 10 19 cm -3 ). As first noticed by Raizer et al [2006], this fact has important consequences for an upward propagating leader, such as in the case of GJs escaping from thundercloud tops. A simple estimate for the streamer zone length L S of an upward propagating leader can be obtained analytically for a simple geometry [da Silva and Pasko, 2013, Figure 1].…”

“…Below, we apply the leader speeds calculated in this paper to the analysis of the GJ development (the leading jet phase). We present a simple time dynamic model for the description of GJ propagation, and finally, we explain the vertical structuring of GJs by combining results of our time dynamic model with the ideas introduced by Raizer et al [2006] and Krehbiel et al [2008].…”

“…[70] Complementarily, Raizer et al [2006Raizer et al [ , 2007 point out that as the GJ leader propagates upward, the streamer zone ahead of it becomes longer and longer because of the dynamics of streamer growth in a medium with exponentially decreasing air density. Theory of leader discharges predicts the existence of an average constant electric field in the streamer zone equal to the critical electric field value for stable streamer propagation E cr [Bazelyan and Raizer, 2000, pp.…”

Underlying mechanisms of transient luminous events: a review

“…Taking into account that τ a ∼ 0.1 µs at the ground level, we obtain τ a ∼ 10 µs at the 18 km altitude, which is typical altitude for BJ nucleation . In this notation, one may expect that the characteristic length of individual streamer, l s ∼ v s τ a (v s is the streamer velocity), cannot be large due to such a small value of τ a (Raizer et al, 2006(Raizer et al, , 2007. For example, a typical length of the streamer filaments propagating inside the sprite is of the order of several meters.…”

“…However, such a large value of the thundercloud charges that is required to sustain the BJ seems to be well-nigh impossible (Mishin and Milikh, 2008;Raizer et al, 2010). Raizer et al (2006Raizer et al ( , 2007 have supposed that BJ can be the result of the formation of a bidirectional uncharged leader at the point where the electric field reaches a maximum value inside the thundercloud (see positive peak shown in Fig. 7).…”