Diffusion model for lightning radiative transfer
Diffusion model for lightning radiative transfer
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DOI：
10.1029/94jd00022
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发表时间：
1994-07
影响因子：
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通讯作者：
W. Koshak;R. Solakiewicz;D. Phanord;R. Blakeslee
中科院分区：
文献类型：
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作者：
W. Koshak;R. Solakiewicz;D. Phanord;R. Blakeslee
采用单速玻耳兹曼输运理论，结合扩散近似，研究了光学厚雷云中闪电的辐射传输特性。近红外(波长=0.7774微米)光子与闪电光谱中一个重要的氧发射三重态有关。将瞬变和空间复杂的闪电辐射源放置在矩形平行六面体雷云内部，研究了多次散射对雷电辐射源的影响。假设云是由相同的球形水滴组成的均匀集合，每个水滴都是近乎保守的各向异性散射体。从概念上讲，我们将雷雨云视为核反应堆，用中子取代光子，并利用核反应堆分析中常见的标准单速中子扩散技术。对于距离震源足够远的区域，得到了强度分布(球谐展开)的有效解析结果。确定了云内闪电信号到达时延和脉宽展宽的模型估计值，其结果与实验数据和以前的蒙特卡罗估计值符合得很好。这类额外的模式研究将用于研究云顶闪电辐射特征的一般信息含量。
A one-speed Boltzmann transport theory, with diffusion approximations, is applied to study the radiative transfer properties of lightning in optically thick thunderclouds. Near-infrared (lambda = 0.7774 micrometers) photons associated with a prominent oxygen emission triplet in the lightning spectrum are considered. Transient and spatially complex lightning radiation sources are placed inside a rectangular parallelepiped thundercloud geometry and the effects of multiple scattering are studied. The cloud is assumed to be composed of a homogeneous collection of identical spherical water droplets, each droplet a nearly conservative, anisotropic scatterer. Conceptually, we treat the thundercloud like a nuclear reactor, with photons replaced by neutrons, and utilize standard one-speed neutron diffusion techniques common in nuclear reactor analyses. Valid analytic results for the intensity distribution (expanded in spherical harmonics) are obtained for regions sufficiently far from sources. Model estimates of the arrival-time delay and pulse width broadening of lightning signals radiated from within the cloud are determined and the results are in good agreement with both experimental data and previous Monte Carlo estimates. Additional model studies of this kind will be used to study the general information content of cloud top lightning radiation signatures.