Plasma motions and non-thermal line broadening in flaring twisted coronal loops
Plasma motions and non-thermal line broadening in flaring twisted coronal loops
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DOI：
10.1051/0004-6361/201527249
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发表时间：
2015-08
期刊：
影响因子：
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通讯作者：
M. Gordovskyy;E. P. Kontar;P. Browning
中科院分区：
文献类型：
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作者：
M. Gordovskyy;E. P. Kontar;P. Browning
观测对不同温度敏感的日冕极紫外线谱线提供了一个机会，以评估燃烧大气中的热结构和流动。这可以用来估计热能和动能之间的分配。我们的目标是模拟大尺度（50- 10000公里）的速度分布，以解释不同光谱EUV线的非热加宽。所开发的模型使我们能够了解所观察到的光谱线偏移和加宽的起源，并将这些特征与燃烧大气中的特定物理效应联系起来。本文用理想MHD方法导出了分层大气中的扭曲磁通管位形。这些磁通管的演变，随后使用电阻MHD，与异常电阻率取决于当地的密度和温度。该模型还考虑了热传导和辐射损失。该模型使我们能够评估平均速度和速度分散，这将被解释为“非热”速度的观测，在不同的温度下的模型的不同部分。我们的模型显示定性和定量的协议与观察。视线（LOS）速度分散表现出与温度的实质性相关性，从约1 MK附近的20-30 km/s增加到约10-20 MK附近的200-400 km/s。平均LOS速度也与速度色散相关，尽管与观测结果相比，它们表现出非常强的散射。我们还注意到，近脚点的速度分散在整个磁场系统低于那些沿着场。我们的结论是，流速，速度分散和温度之间的相关性很可能表明，相同的加热机制是负责加热等离子体，其湍流和膨胀/蒸发。
Observation of coronal EUV spectral lines sensitive to different temperatures offers an opportunity to evaluate the thermal structure and flows in flaring atmospheres. This can be used to estimate the partitioning between the thermal and kinetic energies. Our aim is to model large-scale (50-10000km) velocity distributions in order to interpret non-thermal broadening of different spectral EUV lines. The developed models allow us to understand the origin of the observed spectral line shifts and broadening, and link these features to particular physical effects in flaring atmospheres. We use ideal MHD to derive twisted magnetic fluxtube configurations in a stratified atmosphere. The evolution of these fluxtubes is followed using resistive MHD, with anomalous resistivity depending on the local density and temperature. The model also takes into account the thermal conduction and radiative losses. The model allows us to evaluate average velocities and velocity dispersions, which would be interpreted as `non-thermal' velocities in observations, at different temperatures for different parts of the models. Our models show qualitative and quantitative agreement with observations. The line-of-sight (LOS) velocity dispersions demonstrate substantial correlation with the temperature, increasing from about 20-30 km/s around 1 MK to about 200-400 km/s near 10-20 MK. The average LOS velocities also correlate with velocity dispersions, although they demonstrate a very strong scattering, compared to observations. We also note that near foot-points the velocity dispersions across the magnetic field are systematically lower than those along the field. We conclude, that the correlation between the flow velocities, velocity dispersions and temperatures are likely to indicate that the same heating mechanism is responsible for heating the plasma, its turbulisation and expansion/evaporation.