Radar backscattering from artificial field‐aligned irregularities
Radar backscattering from artificial field‐aligned irregularities
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DOI：
10.1029/1998rs900035
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发表时间：
1999-03
期刊：
影响因子：
1.6
通讯作者：
T. Franz;M. Kelley;A. Gurevich
中科院分区：
文献类型：
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作者：
T. Franz;M. Kelley;A. Gurevich
1992年6月，美国宇航局的一枚探空火箭发射到阿雷西博加热器束中，以提供对人为引起的电离层不规则性的现场观测。本文提供了一种基于现场数据的雷达散射计算方法，并与以往的遥感实验和理论进行了比较。计算出的后向散射截面与先前在50 MHz下对阿雷西博加热器的观测结果吻合良好。更重要的是，当我们适当地缩放观测到的原位功率谱，并将其与科罗拉多普拉特维尔实验的多雷达截面结果进行比较时，我们发现了非常相似的雷达频率依赖性，尽管在较高纬度的站点上，雷达频率依赖性转移到较小的尺度。尽管在阿雷西博和普拉特维尔加热器上的均方根波动水平几乎相同，但在普拉特维尔上尺度向更小结构的转变解释了在那里测量的更大的VHF雷达截面。我们的波形和它的功率谱与最近的一个理论的类似预测的比较显示出良好的一致性，k值高达约5倍的理论预测的频谱中的断点。总之，这些结果提供了非常强有力的证据，证明当高功率无线电波从磁化等离子体反射时，针状孤立结构的产生是占主导地位的最终状态。这些结构的组织尚未解释的过程可以解释的尺度之间的10米和10公里，发生在加热体积。最后，占主导地位的针状场向密度耗尽似乎支持较小尺度不规则性的第二个来源。这造成了幂律斜率的第二次突变，从理论预测的一维k−4.3变为更接近k−3的值。来自普拉特维尔的多雷达结果显示了类似的破裂，我们推测密度和/或温度梯度驱动的不稳定性，如漂移波正在起作用。
In June of 1992 a NASA sounding rocket was fired into the Arecibo heater beam to provide in situ observations of artificially induced ionospheric irregularities. In this paper we provide a radar scattering calculation based on in situ data and compare the same with previous remote sensing experiments and with theory. The calculated backscatter cross section is in good agreement with prior observations over the Arecibo heater at 50 MHz. More important, when we scale the observed in situ power spectrum appropriately and compare it with multiradar cross‐sectional results from the Platteville, Colorado experiments, we find a remarkably similar radar frequency dependence, albeit one shifted to smaller scales over the higher‐latitude site. Even though the rms fluctuation level is almost the same over the Arecibo and Platteville heaters, the shift in scales toward smaller structures over Platteville explains the much larger VHF radar cross section measured there. Comparison of our waveform and its power spectrum with similar predictions from a recent theory shows excellent agreement for k values up to about 5 times the breakpoint in the spectrum of the theoretical prediction. Taken together, these results give very strong evidence for the production of needle‐like solitary structures as the dominant final state when high‐power radio waves reflect from a magnetized plasma. The organization of these structures by as yet unexplained processes may explain the scales between 10 m and 10 km which occur in the heated volume. Finally, the dominant needle‐like field‐aligned density depletions seem to support a second source of smaller‐scale irregularities. This creates a second break in the power law slope from its one‐dimensional value of k−4.3 predicted by theory to one more nearly characterized by k−3. The multiradar results from Platteville show a similar break, and we speculate that a density and/or temperature‐gradient‐driven instability such as the drift wave is operating.