Direct allowance for the effect of photoelectrons in ionospheric modeling
Direct allowance for the effect of photoelectrons in ionospheric modeling
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DOI：
10.1029/95ja02358
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发表时间：
1996
影响因子：
--
通讯作者：
J. Titheridge
中科院分区：
文献类型：
--
作者：
J. Titheridge
如果不考虑初级光电子产生二次电离，电离层 E 和 F1 区域的模型计算得出的电子密度太小。完全计算这种二次产生是相当困难的，因为向上和向下的光电子通量必须确定为每个高度的能量的函数。早期研究表明，二次电离使 F2 区域的总生产率提高了约 30%，而最近的研究表明，E 和 F1 区域的总生产率提高了约 100%。然而，使用固定的校正因子（对于给定的高度和天顶角）并不令人满意，因为二次生产的量对于不同的辐射带变化很大。本文描述了一种新方法，其中确定每个离子和每个辐射带的次级产生因子。这些因子 (ns) 由初始光子能量和最终二次电子的平均能量定义。对于每个辐射带，每个离子的有效生产效率增加 1 + ns。然后，电离层建模正常进行，没有其他变化，也没有增加计算机时间。对于天顶角、大气模型或 EUV 通量的任何假设值，所有结果都会自动包含二次生产的全部余量。与最近的完整光电子计算的比较表明，该过程给出了可靠的结果，其误差小于由于太阳通量、光电离截面和电子碰撞截面的当前不确定性而导致的误差。
Model calculations for the ionospheric E and F1 regions yield electron densities which are much too small, if no allowance is made for the production of secondary ionization by primary photoelectrons. Full calculations of this secondary production are quite difficult, since the upward and downward photoelectron fluxes must be determined as a function of energy at each height. Early studies showed that secondary ionization increases the total production rate by about 30% in the F2 region, while more recent studies show increases of around 100% in the E and F1 regions. Use of a fixed correction factor (for a given height and zenith angle) is not satisfactory, however, since the amount of secondary production varies greatly for different radiation bands. This paper describes a new approach in which a secondary production factor is determined for each ion and each radiation band. These factors (ns) are defined by the initial photon energy, and the mean energy of the final secondary electrons. For each radiation band the effective production efficiencies, for each ion, are increased by the factor 1 + ns. Modeling of the ionosphere then proceeds normally, with no other changes and no increase in computer time. All results automatically include a full allowance for secondary production, for any assumed values of zenith angle, atmospheric model, or EUV fluxes. Comparison with recent, full photoelectron calculations shows that this procedure gives reliable results, with errors which are less than those due to current uncertainties in the solar fluxes, the photoionization cross sections and the electron collision cross sections.