Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements
Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements
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DOI：
10.1007/s11207-014-0543-5
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发表时间：
2014-04
期刊：
影响因子：
2.8
通讯作者：
K. Nagashima;B. Löptien;L. Gizon;A. Birch;R. Cameron;S. Couvidat;S. Danilovic;B. Fleck;R. Stein
中科院分区：
文献类型：
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作者：
K. Nagashima;B. Löptien;L. Gizon;A. Birch;R. Cameron;S. Couvidat;S. Danilovic;B. Fleck;R. Stein
太阳动力学天文台/日震和磁成像仪（SDO/HMI）的滤波图，采取了六个波长周围的Fei6173.3太阳能谱线，包含有关的视线速度在太阳大气层的高度范围内的信息。从这些观测中得到的多高度速度推论可用于研究大气中的波动和能量输运。使用现实的对流模拟数据集提供的STAGGER和MURaM代码，我们生成合成滤波图，并探讨几种方法估计多普勒。我们调查在哪个高度每个合成多普勒相关性最强的垂直速度在模型大气。在调查的基础上，我们提出了两个Dopplergram以外的标准HMI算法Dopplergram从HMI滤波：线中心Dopplergram和平均翼Dopplergram。这两个多普勒图与HMI算法多普勒图的有效高度以上30 - 40公里（线中心）和以下30 - 40公里（平均机翼）高度处的垂直速度相关性最强。因此，我们最多可以从大气中相隔约半个尺度高度的两层中获得速度信息。这些多高度多普勒从观测数据以及从模拟数据之间的相移也是一致的高度差估计的频率范围以上的光球声截止频率。
TheSolar Dynamics Observatory/Helioseismic and Magnetic Imager(SDO/HMI) filtergrams, taken at six wavelengths around the Fei6173.3 Å line, contain information about the line-of-sight velocity over a range of heights in the solar atmosphere. Multi-height velocity inferences from these observations can be exploited to study wave motions and energy transport in the atmosphere. Using realistic convection-simulation datasets provided by the STAGGER and MURaM codes, we generate synthetic filtergrams and explore several methods for estimating Dopplergrams. We investigate at which height each synthetic Dopplergram correlates most strongly with the vertical velocity in the model atmospheres. On the basis of the investigation, we propose two Dopplergrams other than the standard HMI-algorithm Dopplergram produced from HMI filtergrams: a line-center Dopplergram and an average-wing Dopplergram. These two Dopplergrams correlate most strongly with vertical velocities at the heights of 30 – 40 km above (line center) and 30 – 40 km below (average wing) the effective height of the HMI-algorithm Dopplergram. Therefore, we can obtain velocity information from two layers separated by about a half of a scale height in the atmosphere, at best. The phase shifts between these multi-height Dopplergrams from observational data as well as those from the simulated data are also consistent with the height-difference estimates in the frequency range above the photospheric acoustic-cutoff frequency.