Skeltved Alexander Broberg, Østgaard Nikolai, Mezentsev Andrew, Lehtinen Nikolai, Carlson Brant
Birkeland Centre for Space Science, Institute of Physics and Technology University of Bergen Bergen Norway.
Physics and Astronomy Carthage College Kenosha Wisconsin USA.
J Geophys Res Atmos. 2017 Aug 16;122(15):8120-8134. doi: 10.1002/2016JD026206. Epub 2017 Aug 5.
Several computer models exist to explain the observation of terrestrial gamma-ray flashes (TGFs). Some of these models estimate the electric field ahead of lightning leaders and its effects on electron acceleration and multiplication. In this paper, we derive a new set of constraints to do more realistic modeling. We determine initial conditions based on in situ measurements of electric field and vertical separation between the main charge layers of thunderclouds. A maximum electric field strength of 50 kV/cm at sea level is introduced as the upper constraint for the leader electric field. The threshold for electron avalanches to develop of 2.86 kV/cm at sea level is introduced as the lower value. With these constraints, we determine a region where acceleration and multiplication of electrons occur. The maximum potential difference in this region is found to be ∼52 MV, and the corresponding number of avalanche multiplication lengths is ∼3.5. We then quantify the effect of the ambient electric field compared to the leader field at the upper altitude of the negative tip. Finally, we argue that only leaders with the highest potential difference between its tips (∼600 MV) can be candidates for the production of TGFs. However, with the assumptions we have used, these cannot explain the observed maximum energies of at least 40 MeV. Open questions with regard to the temporal development of the streamer zone and its effect on the shape of the electric field remain.
现有多种计算机模型来解释地面伽马射线闪光（TGFs）的观测结果。其中一些模型估算了闪电先导前方的电场及其对电子加速和倍增的影响。在本文中，我们推导了一组新的约束条件，以便进行更实际的建模。我们根据对电场的原位测量以及雷云主电荷层之间的垂直间距来确定初始条件。引入海平面处50 kV/cm的最大电场强度作为先导电场的上限约束。引入海平面处电子雪崩发展的阈值2.86 kV/cm作为下限值。利用这些约束条件，我们确定了电子发生加速和倍增的区域。发现该区域的最大电位差约为52 MV，相应的雪崩倍增长度数量约为3.5。然后，我们在负尖端的较高海拔处，将环境电场与先导电场的影响进行了量化比较。最后，我们认为只有尖端之间电位差最高（约600 MV）的先导才可能是产生TGFs的候选者。然而，基于我们所采用的假设，这些无法解释观测到的至少40 MeV的最大能量。关于流光区的时间发展及其对电场形状的影响，仍然存在一些未解决的问题。
