基于中纬度雷达观测的2013 - 2017年X射线太阳耀斑期间低纬天空噪声的衰减
Attenuation of decameter sky noise during x-ray solar flares in 2013-2017 based on the observations at midlatitude radars
摘要：
基于对10个中纬度纬度低纬雷达数据的联合分析，研究了2013 - 2017年期间80次X射线耀斑的影响。为了进行研究，使用了北半球的9个中纬度SuperDARN雷达和ISTP SB RAS的叶卡捷琳堡相干多普勒雷达。所有雷达都工作在相同的8 - 20MHz频段，并具有类似的硬件和软件。在分析过程中，分别研究了来自每个雷达方向和每个耀斑的噪声的时间动态。结果，在每天约13000次测量的基础上，我们发现噪声功率和x射线耀斑强度之间存在很强的相关性，这使得我们可以利用短波天空噪声来诊断x射线太阳耀斑的电离层效应。结果表明，在太阳耀斑期间，有88.3%的观测到日间射电噪声的衰减，这与太阳耀斑的时间动力学有关。在33%的情况下，日间观测到的衰减噪声强度与太阳高度角$>0$的X射线耀斑形状有良好的相关性（Pearson相关系数大于-0.5），日间平均Pearson相关系数约为-0.34。GOES 0.1 - 0.8nm X射线强度与白天天空噪声衰减的回归系数中值约为$-4.4\cdot10^{4}\ [dB\cdot m^{2}/Wt]$。因此，已经表明，在中纬度的十纬雷达上对十纬天空噪声水平的测量可用于研究X射线太阳耀斑期间低电离层对高频波的电离层吸收。这可以通过以下假设来解释：由雷达检测到的十月天空噪声的大部分可以被解释为由第一传播跳距（\textasciitilde{} 3000 km）处的地面源产生。
英文摘要：
Based on a joint analysis of the data from 10 midlatitude decameter radars the effects are investigated during 80 x-ray flares in the period 2013-2017. For the investigation nine mid-latitude SuperDARN radars of the northern hemisphere and Ekaterinburg coherent decameter radar of ISTP SB RAS are used. All the radars work in the same 8-20MHz frequency band and have similar hardware and software. During the analysis the temporal dynamics of noise from each of the radar direction and for each flare is investigated separately. As a result, on the basis of about 13000 daily measurements we found a strong anticorrelation between noise power and x-ray flare intensity, that allows to use short-wave sky noise to diagnose the ionospheric effects of x-ray solar flares. It is shown that in 88.3\% of cases an attenuation of daytime decameter radio noise is observed during solar flare, correlating with the temporal dynamics of the solar flare. The intensity of decameter noise anticorrelates well (the Pearson correlation coefficient better than -0.5) with the shape of the X-ray flare in the daytime (for solar elevation angle $>0$) in 33\% of cases, the average Pearson correlation over the daytime is about -0.34. Median regression coefficient between GOES 0.1-0.8nm x-ray intensity and daytime sky-noise attenuation is about $-4.4\cdot10^{4}\ [dB\cdot m^{2}/Wt]$. Thus, it has been shown that measurements of the decameter sky noise level at midlatitude decameter radars can be used to study the ionospheric absorption of high-frequency waves in the lower ionosphere during x-ray solar flares. This can be explained by the assumption that the most part of decameter sky noise detected by the radars can be interpreted as produced by ground sources at distances of the first propagation hop (\textasciitilde{} 3000 km).
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