A nanoflare model of quiet Sun EUV emission
A nanoflare model of quiet Sun EUV emission
复制标题
安静太阳 EUV 发射的纳米耀斑模型
DOI：
10.1051/0004-6361:20065152
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发表时间：
2006
影响因子：
6.5
通讯作者：
S. Solanki
中科院分区：
文献类型：
--
作者：
A. Pauluhn;S. Solanki
纳米耀斑被认为是太阳日冕加热的主要来源。然而，到目前为止，直接探测到它们被证明是难以捉摸的，并且从更大的亮斑的特性来推断它们，对表征它们分布的幂律指数α的估计是不可靠的。
在这里，我们采取统计建模的方法，代表安静的太阳，如在极紫外光辐射中看到的光曲线。基本假设是，所有安静太阳的极紫外光发射都是由于微和纳米耀斑，其辐射能量呈幂律分布。
安静太阳的亮度值遵循对数正态分布。这与分布是在空间扫描上还是在时间序列上是无关的。我们证明这些分布可以用我们的简单模型再现。通过同时拟合从过渡区和日冕线发射的光曲线得到的亮度分布函数和功率谱，约束了微、纳米耀斑亮度的幂律分布。纳米耀斑能量呈陡幂律分布，幂律指数为$\alpha> 2$，与测量结果有很好的统计匹配。这与向日冕输入的主要热量是由纳米耀斑提供的一致，即由能量约为10 23尔格的事件提供的热量。为了重现观测到的SUMER时间序列，在安静的太阳大气中，每秒大约需要103到104个纳米耀斑（假设纳米耀斑覆盖的平均面积为10 13平方米）。
Nanoflares have been proposed as the main source of heating of the solar corona. However, detecting them directly has so far proved elusive, and extrapolating to them from the properties of larger brightenings gives unreliable estimates of the power-law exponent α characterising their distribution.
Here we take the approach of statistically modelling light curves representative of the quiet Sun as seen in EUV radiation. The basic assumption is that all quiet-Sun EUV emission is due to micro- and nanoflares, whose radiative energies display a power-law distribution.
Radiance values in the quiet Sun follow a lognormal distribution. This is irrespective of whether the distribution is made over a spatial scan or over a time series. We show that these distributions can be reproduced by our simple model. By simultaneously fitting the radiance distribution function and the power spectrum obtained from the light curves emitted by transition region and coronal lines the power-law distribution of micro- and nanoflare brightenings is constrained. A good statistical match to the measurements is obtained for a steep power-law distribution of nanoflare energies, with power-law exponent $\alpha> 2$. This is consistent with the dominant heat input to the corona being provided by nanoflares, i.e., by events with energies around 10 23 erg. In order to reproduce the observed SUMER time series approximately 10 3 to 10 4 nanoflares are needed per second throughout the atmosphere of the quiet Sun (assuming the nanoflares to cover an average area of 10 13 m 2 ).