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首页> 外文期刊>Astrophysics and space science >Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares
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Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares

机译：从X射线太阳耀斑的VLF信号幅度及其时延评估低纬度D区电离层的有效重组系数和太阳天顶角效应

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Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (ΔA) and amplitude time delay (Δt) (vis-á-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22° 27′N, 87° 45′E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (α _(eff)) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δt). For the C-class flares we find that there is a direct correspondence between Δt of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δt for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux φ{symbol} _(max) independent of these time slots, the goodness of fit, as measured by reduced-χ ~2, actually worsens as the day progresses. The variation of the Z dependence of reduced-χ ~2 seems to follow the variation of standard deviation of Z along the T _x-R_x propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Δt and φ{symbol} max was observed.
机译：太阳耀斑期间过多的太阳X射线辐射会导致电离层D区域的电离增强，从而影响电离层以下传播的VLF信号幅度和相位。我们已经为太阳耀斑计算了NWC / 19.8 kHz信号的VLF信号振幅扰动（ΔA）和振幅时间延迟（Δt）（相对于对应的X射线光曲线，由GOES-15测量）。在2011年1月9日期间。信号由印度西孟加拉邦Sitapur（22°27′N，87°45′E）的IERC / ICSP的SoftPAL设备记录。在工作的第一部分中，我们使用众所周知的LWPC技术，通过振幅扰动方法模拟了耀斑引起的过低的电离层电子密度。还可以通过仿真获得不受干扰的D区电子密度，并将其与IRI模型结果进行比较。使用这些模拟结果和时间延迟作为关键参数，我们计算了太阳耀斑峰值区域的有效电子复合系数（α_（eff））。我们的结果与其他已建立模型获得的结果相匹配。在第二部分中，我们讨论了耀斑期间太阳天顶角对D区的影响。我们将此VLF数据与太阳X射线数据相关联。我们发现，对于每个耀斑，VLF振幅的峰值都晚于X射线峰值的时间。我们研究了这种所谓的时间延迟（Δt）。对于C级耀斑，我们发现在耀斑发生时，太阳耀斑的Δt与信号传播路径上的平均太阳天顶角Z有直接的对应关系。现在进行更深入的分析，我们针对不同的本地昼夜时隙DT计算Δt。我们发现，尽管时间延迟与火炬峰值能量通量φ{symbol} _（max）无关，而与这些时隙无关，但拟合优度（由减少的χ〜2衡量）实际上随着时间的推移而变差。进展。减少的χ〜2的Z依赖性的变化似乎遵循Z的标准偏差沿着T _x-R_x传播路径的变化。换句话说，对于在路径上具有几乎恒定的Z的耀斑，观察到Δt和φ{symbol} max之间更紧密的反相关。

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