arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2403.02110astro-ph.SR
收藏

广义冕环标度律及其对太阳活动区环中湍流的启示

Generalized Coronal Loop Scaling Laws and Their Implication for Turbulence in Solar Active Region Loops

Y. Dai, J. J. Xiang, M. D. Ding

AI总结:

本文推广含库仑碰撞与湍流散射的混合冕环模型,引入温度幂律形式的非均匀加热和横截面,建立环顶温度与加热率标度律,解释足点加热及截面膨胀对湍流依赖的调节作用。

摘要:

近期的冕环建模强调,结合库仑碰撞与湍流散射来刻画沿磁场热传导非常重要,这引出了混合环模型。在本工作中,我们通过引入非均匀加热和横截面来推广该混合模型,二者均表示为温度的幂律函数。基于混合模型解,我们构建了将环顶温度($T_a$)和加热率($H_a$)与其他环参数联系起来的标度律。研究发现,湍流环的环顶性质另外还是湍流平均自由程($λ_T$)的幂律函数,其函数形式随情形而变,取决于加热和/或面积参数的具体设定。更重要的是,足够集中于足点的加热以及随高度发生的横截面膨胀,都能有效削弱(增强)$T_a$($H_a$)对$λ_T$的负(正)幂律依赖。其原因在于,足点加热和/或横截面膨胀显著降低了以湍流为主的日冕部分中的热流;在该部分,湍流散射使传导系数对温度的依赖弱得多。因此,在这一区域,热流的降低主要依赖于温度梯度向后变平。通过纳入更真实条件的数值建模,这一情景得到进一步巩固。我们的结果对太阳活动区(AR)环具有重要启示。考虑非均匀加热和横截面因素后,AR环可以承受相对更强的湍流,同时仍保持非耀斑环在物理上合理的温度。

英文摘要:

Recent coronal loop modeling has emphasized the importance of combining both Coulomb collisions and turbulent scattering to characterize field-aligned thermal conduction, which invokes a hybrid loop model. In this work we generalize the hybrid model by incorporating nonuniform heating and cross section that are both formulated by a power-law function of temperature. Based on the hybrid model solutions, we construct scaling laws that relate loop-top temperature ($T_a$) and heating rate ($H_a$) to other loop parameters. It is found that the loop-top properties for turbulent loops are additionally power-law functions of turbulent mean free path ($λ_T$), with the functional forms varying from situation to situation that depends on the specification of the heating and/or areal parameters. More importantly, both a sufficiently footpoint-concentrated heating and a cross-sectional expansion with height can effectively weaken (strengthen) the negative (positive) power-law dependence of $T_a$ ($H_a$) on $λ_T$. The reason lies in a notable reduction of heat flux by footpoint heating and/or cross-sectional expansion in the turbulence-dominated coronal part, where turbulent scattering introduces a much weaker dependence of the conduction coefficient on temperature. In this region, therefore, the reduction of the heat flux predominately relies on a backward flattening of the temperature gradient. Through numerical modeling that incorporates more realistic conditions, this scenario is further consolidated. Our results have important implication for solar active region (AR) loops. With the factors of nonuniform heating and cross section taken into account, AR loops can bear relatively stronger turbulence while still keeping a physically reasonable temperature for nonflaring loops.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑