Evidence for Wind-like Regions, Acceleration of Shocks in the Deep Corona, and Relevance of 1/f Dynamic Spectra to Coronal Type II Bursts
Evidence for Wind-like Regions, Acceleration of Shocks in the Deep Corona, and Relevance of 1/f Dynamic Spectra to Coronal Type II Bursts
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类风区域的证据、深日冕中的冲击加速以及 1/f 动态光谱与日冕 II 型爆发的相关性
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发表时间：
2008
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影响因子：
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通讯作者：
P. Robinson
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作者：
V. Lobzin;I. Cairns;P. Robinson
II型射电暴是在本地等离子体频率fp附近和2fp附近产生的，是由穿过日冕和太阳风的激波产生的。本文分析了8个明确定义的日冕II型射电暴（30-300 MHz）。给出了三个结果。首先，发现中心频率对时间的依赖关系可以拟合为幂律模型f∝(t−t0)−α，函数值为0.6≤α≤1.3。假设激波速度恒定，这些结果证明了II型源区的密度分布ne(r)与太阳风非常相似，ne(r)∝r−2。一种可能的解释是太阳风开始于光球圈的几个太阳半径内，最有可能在一个太阳半径内。另一个依赖于气体动力学Whitham分析，并证明了爆炸冲击加速的可能性，从而将明显的幂律指数降低到类似太阳风的值。其次，对于所考虑的事件，发现射电暴发射以1/f对t动态光谱的形式密切遵循直线。在未来，这将允许在太阳射电数据中更客观地识别II型爆发，并与日冕仪和其他太阳雷达进行合理的实时关联。第三，证明了1/f vs . t动态光谱可以为日冕深处激波加速提供直接证据，从而补充了日冕仪的研究。
Type II radio bursts are produced near the local plasma frequency fp and near 2fp by shocks moving through the corona and solar wind. In the present Letter eight well-defined coronal type II radio bursts (30-300 MHz) are analyzed. Three results are presented. First, it is found that the dependence of the central frequency on time can be fitted to a power-law model, f ∝ (t − t0)−α, with 0.6 ⩽ α ⩽ 1.3. Assuming a constant shock velocity, these results provide evidence that the density profile ne(r) in the type II source regions closely resembles the solar wind, with ne(r) ∝ r−2. One possible interpretation is that the solar wind starts within a few solar radii of the photosphere, most probably within 1 solar radius. Another relies on a gasdynamic Whitham analysis and demonstrates a possibility for blast shocks to accelerate, thereby reducing apparent power-law indices to solar wind-like values. Second, for the events considered it is found that radio burst emission in the form of 1/f versus t dynamic spectra closely follows straight lines. In future this will allow much more objective identification of type II bursts in solar radio data and plausibly real-time correlation with coronagraph and other solar radar. Third, it is demonstrated that 1/f versus t dynamic spectra can provide direct evidence for acceleration of the shock deep in the corona, thus complementing coronagraph studies.