ELECTRON HEAT FLUX IN THE SOLAR WIND: ARE WE OBSERVING THE COLLISIONAL LIMIT IN THE 1 AU DATA?
ELECTRON HEAT FLUX IN THE SOLAR WIND: ARE WE OBSERVING THE COLLISIONAL LIMIT IN THE 1 AU DATA?
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太阳风中的电子热通量：我们是否观察到 1 AU 数据中的碰撞极限？
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
F. Pantellini
中科院分区：
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作者：
S. Landi;L. Matteini;F. Pantellini
使用1 AU的统计显著数据，它最近已被显示(Bale等人)。在太阳风中，当Knudsen数KT(电子平均自由程与电子温度标度高度之比)降到约0.3以下时，电子热流密度Q迅速接近经典的碰撞Spitzer-Härm极限。利用一个包括库仑碰撞和太阳风随日心距离膨胀的全动力学模型，我们观察到当克努森数小于约0.3时，热流强度确实接近碰撞值，这与观测结果非常一致。然而，进一步考察热流密度性质，如热流密度随日心距的变化及其与等离子体参数的关系，发现对于0.02到0.3之间的克努森数，热流密度不能用Spitzer-Härm公式来描述。我们的结论是，尽管在1AU的观测似乎表明，当克努森下降到∼0.3时，电子热流密度接近碰撞极限，但对于大于0.01时，碰撞极限并不是通常有效的闭合。此外，在高Knudsen数区，我们模型的热通量与太阳风测量的热通量之间的良好一致性似乎表明，1AU处的热通量不受电磁不稳定性的限制，因为我们的计算忽略了波-粒子和波-波相互作用。
Using statistically significant data at 1 AU, it has recently been shown (Bale et al.) that in the solar wind, when the Knudsen number KT (the ratio between the electron mean free path and the electron temperature scale height) drops below about 0.3, the electron heat flux q intensity rapidly approaches the classical collisional Spitzer–Härm limit. Using a fully kinetic model including the effect of Coulomb collisions and the expansion of the solar wind with heliocentric distance, we observe that the heat flux strength does indeed approach the collisional value for Knudsen numbers smaller than about 0.3 in very good agreement with the observations. However, closer inspection of the heat flux properties, such as its variation with the heliocentric distance and its dependence on the plasma parameters, shows that for Knudsen numbers between 0.02 and 0.3 the heat flux is not conveniently described by the Spitzer–Härm formula. We conclude that even though observations at 1 AU seem to indicate that the electron heat flux intensity approaches the collisional limit when the Knudsen drops below ∼0.3, the collisional limit is not a generally valid closure for a Knudsen larger than 0.01. Moreover, the good agreement between the heat flux from our model and the heat flux from solar wind measurements in the high-Knudsen number regime seems to indicate that the heat flux at 1 AU is not constrained by electromagnetic instabilities as both wave–particle and wave–wave interactions are neglected in our calculations.