Dynamics of Magnetic Flux Elements in the Solar Photosphere
Dynamics of Magnetic Flux Elements in the Solar Photosphere
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DOI：
10.1086/306471
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发表时间：
1998-02
期刊：
影响因子：
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通讯作者：
A. A. Ballegooijen-A.;P. Nisenson;R. Noyes;Mats G. Lofdahl;R. Stein;Å. Nordlund;V. Krishnakumar
中科院分区：
文献类型：
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作者：
A. A. Ballegooijen-A.;P. Nisenson;R. Noyes;Mats G. Lofdahl;R. Stein;Å. Nordlund;V. Krishnakumar
在日冕加热问题的背景下研究了磁场和对流的相互作用。我们使用拉帕尔马瑞典真空太阳望远镜获得的高分辨率 G 波段和连续滤光图的时间序列来研究光球磁性元件的运动。 G 带图像显示以线性结构（“细丝”）排列的亮点，这些亮点位于相邻颗粒细胞之间的泳道中。我们使用对象跟踪技术测量这些亮点的运动，并确定描述亮点速度随时间变化的自相关函数。速度的相关时间约为100 s。为了了解确定亮点空间分布的过程，我们对磁通量元素响应太阳粒化流的水平运动进行了模拟。造粒流模型是使用简单的二维模型从观察到的造粒强度图像导出的，该模型包括惯性和水平温度梯度；假设磁通量元件被该粒化流被动地平流输送。结果表明，这种被动平流模型与观测结果相当一致，表明在 1 小时的时间尺度上，通量管并未受到大深度锚固的强烈影响。最后，我们使用势场建模将磁场和速度场外推到更大的高度。我们发现色球层中的速度可以在相邻通量管之间的分界面处局部增强。预测的速度为几公里·秒-1，明显大于光球通量管的速度。讨论了这些结果对日冕加热的影响。
The interaction of magnetic fields and convection is investigated in the context of the coronal heating problem. We study the motions of photospheric magnetic elements using a time series of high-resolution G-band and continuum filtergrams obtained at the Swedish Vacuum Solar Telescope at La Palma. The G-band images show bright points arranged in linear structures ("filigree") located in the lanes between neighboring granule cells. We measure the motions of these bright points using an object tracking technique, and we determine the autocorrelation function describing the temporal variation of the bright point velocity. The correlation time of the velocity is about 100 s. To understand the processes that determine the spatial distribution of the bright points, we perform simulations of horizontal motions of magnetic flux elements in response to solar granulation flows. Models of the granulation flow are derived from the observed granulation intensity images using a simple two-dimensional model that includes both inertia and horizontal temperature gradients; the magnetic flux elements are assumed to be passively advected by this granulation flow. The results suggest that this passive advection model is in reasonable agreement with the observations, indicating that on a timescale of 1 hr the flux tubes are not strongly affected by their anchoring at large depth. Finally, we use potential-field modeling to extrapolate the magnetic and velocity fields to larger height. We find that the velocity in the chromosphere can be locally enhanced at the separatrix surfaces between neighboring flux tubes. The predicted velocities are several km s-1, significantly larger than those of the photospheric flux tubes. The implications of these results for coronal heating are discussed.