Modeling of coronal EUV loops observed with TRACE.: I.: Hydrostatic solutions with nonuniform heating
Modeling of coronal EUV loops observed with TRACE.: I.: Hydrostatic solutions with nonuniform heating
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DOI：
10.1086/319796
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发表时间：
2001-04-01
影响因子：
4.9
通讯作者：
Alexander, D
中科院分区：
文献类型：
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作者：
Aschwanden, MJ;Schrijver, CJ;Alexander, D
最近用过渡区和日冕探测器（TRACE）以及太阳和日光层天文台（SOHO）上的极紫外成像望远镜（EIT）对极紫外波长的日冕环进行的观测表明了三个新的结果，这些结果无法用大多数现有的环模型来解释：（1）EUV环沿其冠状段沿着是近等温的，（2）与具有均匀加热的稳态环的要求相比，它们显示出过压或过密度，（3）最亮的EUV环显示出扩展的标度高度，高达流体静力学标度高度的4倍。这些观测结果与经典的RTV（Rosner，Tucker，& Vaiana）模型不一致，它们不支持均匀加热的模型，甚至部分违反了流体静力平衡的要求。在这项研究中，我们第一次拟合的流体动力学方程的稳态解观察到的强度分布，允许详细的一致性测试所观察到的温度T（s）和密度分布n（e）（s）与稳态模型，这是不可能的，在以前的研究的基础上标度律。我们计算了大约500个流体静力学解，它们覆盖了非均匀加热函数（加热标度高度在λ（H）的范围内，近似为1-300 μ m）的环路长度（L近似为4-300 μ m）的大参数空间，也接近均匀加热的极限（λ（H）远大于L）。参数空间可以被细分为三个区域，其包含（1）稳定分层回路的解，（2）不稳定分层回路的解（在短加热标度高度的情况下，lambda（H，Mm）近似于rootL（Mm）），以及（3）其中我们找不到数值解的区域（当lambda（H），（Mm）小于或类似于rootL（Mm）时）。拟合流体静力学的解决方案，以41极紫外线回路观察TRACE（选择的标准，在其整个长度的可探测性），我们发现，只有30%的循环是一致的流体静力学的稳态解决方案。没有一个观察到的EUV环路是一致的，而在准稳态的均匀加热功能。发现与稳态相容的那些回路在足点附近被加热，加热标度高度为lambda（H）= 12 +/- 5 μ m，覆盖回路长度的分数lambda（H）/L = 0.2 +/- 0.1。这些结果支持日冕加热机制在色球层和过渡区或附近的操作。
Recent observations of coronal loops in EUV wavelengths with the Transition Region and Coronal Explorer (TRACE) and the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) demonstrated three new results that cannot be explained by most of the existing loop models: (1) EUV loops are near-isothermal along their coronal segments, (2) they show an overpressure or overdensity compared with the requirements of steady state loops with uniform heating, and (3) the brightest EUV loops exhibit extended scale heights up to 4 times the hydrostatic scale height. These observations cannot be reconciled with the classical RTV (Rosner, Tucker, & Vaiana) model, they do not support models with uniform heating, and they even partially violate the requirements of hydrostatic equilibrium. In this study we are fitting for the first time steady state solutions of the hydrodynamic equations to observed intensity profiles, permitting a detailed consistency test of the observed temperature T(s) and density profiles n(e)(s) with steady state models, which was not possible in previous studies based on scaling laws. We calculate some 500 hydrostatic solutions, which cover a large parameter space of loop lengths (L approximate to 4-300 Mm), of nonuniform heating functions (with heating scale heights in the range of lambda (H) approximate to 1-300 Mm), approaching also the limit of uniform heating (lambda (H) much greater than L). The parameter space can be subdivided into three regimes, which contain (1) solutions of stably stratified loops, (2) solutions of unstably stratified loops (in the case of short heating scale heights, lambda (H, Mm) approximate to rootL(Mm)), and (3) a regime in which we find no numerical solutions (when lambda (H), (Mm) less than or similar to rootL(Mm)). Fitting the hydrostatic solutions to 41 EUV loops observed with TRACE (selected by the criterion of detectability over their entire length), we find that only 30% of the loops are consistent with hydrostatic steady state solutions. None of the observed EUV loops is consistent with a uniform heating function while in quasi-steady state. Those loops compatible with a steady state are found to be heated near the footpoints, with a heating scale height of lambda (H) = 12 +/- 5 Mm, covering a fraction lambda (H)/L = 0.2 +/- 0.1 of the loop length. These results support coronal heating mechanisms operating in or near the chromosphere and transition region.