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首页> 外文期刊>Solar Physics >Transverse Oscillations in Coronal Loops Observed with TRACE – II. Measurements of Geometric and Physical Parameters
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Transverse Oscillations in Coronal Loops Observed with TRACE – II. Measurements of Geometric and Physical Parameters

机译：用TRACE – II观测到的冠状环中的横向振荡。几何和物理参数的测量

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摘要

We measure geometric and physical parameters oftransverse oscillations in 26 coronal loops, out of the 17 events described in Paper I by Schrijver, Aschwanden, and Title (2002). These events, lasting from 7 to 90 min, have been recorded with the Transition Region and Coronal Explorer (TRACE) in the 171 and 195 Å wavelength bands with a characteristic angular resolution of 1", with time cadences of 15–75 seconds. We estimate the unprojected loop (half) length L and orientation of the loop plane, based on a best-fit of a circular geometry. Then we measure the amplitude A(t) of transverse oscillations at the loop position with the largest amplitude. We decompose the time series of the transverse loop motion into an oscillating component A osc(t) and a slowly-varying trend A trend(t). We find oscillation periods in the range of P=2–33 min, transverse amplitudes of A=100–8800 km, loop half lengths of L=37 000–291 000 km, and decay times of t d=3.2–21 min. We estimate a lower limit of the loop densities to be in the range of n loop=0.13–1.7×109 cm−3. The oscillations show (1) strong deviations from periodic pulses, (2) spatially asymmetric oscillation amplitudes along the loops, and (3) nonlinear transverse motions of the centroid of the oscillation amplitude. From these properties we conclude that most of the oscillating loops do not fit the simple model of kink eigen-mode oscillations, but rather manifest flare-induced impulsively generated MHD waves, which propagate forth and back in the loops and decay quickly by wave leakage or damping. In contrast to earlier work we find that the observed damping times are compatible with estimates of wave leakage through the footpoints, for chromospheric density scale heights of ≈400–2400 km. We conclude that transverse oscillations are most likely excited in loops that (1) are located near magnetic nullpoints or separator lines, and (2) are hit by a sufficiently fast exciter. These two conditions may explain the relative rarity of detected loop oscillations. We show that coronal seismology based on measurements of oscillating loop properties is challenging due to the uncertainties in estimating various loop parameters. We find that a more accurate determination of loop densities and magnetic fields, as well as advanced numerical modeling of oscillating loops, are necessary conditions for true coronal seismology.
机译：我们在Schrijver，Aschwanden和Title（2002）在论文I中描述的17个事件中，测量了26个冠状环中横向振荡的几何和物理参数。这些事件持续7到90分钟，已在171和195Å波段以过渡区和日冕总管（TRACE）记录，特征角分辨率为1“，时间节奏为15-75秒。根据圆形几何的最佳拟合估计未投影的环路（半）长度L和环路平面的方向，然后测量最大振幅的环路位置处横向振动的振幅A（t）。横波运动到一个振荡分量A osc （t）和一个缓慢变化的趋势A趋势（t）的时间序列。我们发现振荡周期在P = 2-33的范围内min，横向振幅为A = 100–8800 km，半圈长度为L = 37 000–291 000 km，衰减时间为td = 3.2–21 min，我们估算出环密度的下限为处于n环范围内 = 0.13–1.7×109 cm−3 。振荡显示（1）与周期脉冲的强烈偏离，（2）在空间上a沿着环路的对称振幅，以及（3）振幅振幅质心的非线性横向运动。根据这些特性，我们得出结论，大多数振荡回路不适合扭结本征模式振荡的简单模型，而是表现出耀斑感应脉冲产生的MHD波，它们在回路中来回传播，并由于漏波或漏电而迅速衰减。阻尼。与早期的工作相比，我们发现，对于色球层密度标高为≈400–2400 km的情况，观测到的阻尼时间与通过脚点的波泄漏估计值兼容。我们得出结论，横向振荡最有可能在以下回路中被激发：（1）位于磁性零点或分隔线附近，而（2）被足够快的激励器击中。这两个条件可以解释检测到的环路振荡的相对稀有性。我们表明，由于估算各种回路参数的不确定性，基于振荡回路特性测量的日冕地震学具有挑战性。我们发现，更准确地确定环的密度和磁场以及振荡环的高级数值模型是真正的日冕地震学的必要条件。

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  • 来源
    《Solar Physics》 |2002年第1期|99-132|共34页
  • 作者

    Markus J. Aschwanden; Bart De Pontieu; Carolus J. Schrijver; Alan M. Title;

  • 作者单位

    Solar and Astrophysics Laboratory Department L9-41 Lockheed Martin Advanced Technology Center;

    Solar and Astrophysics Laboratory Department L9-41 Lockheed Martin Advanced Technology Center;

    Solar and Astrophysics Laboratory Department L9-41 Lockheed Martin Advanced Technology Center;

    Solar and Astrophysics Laboratory Department L9-41 Lockheed Martin Advanced Technology Center;

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