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Radial Flows in Supergranules

机译：超颗粒中的径向流

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摘要

We determine the radial component of the supergranular flow velocity by examining the center-to-limb variation of the Doppler velocity signal. We acquire individual Doppler images obtained with the MDI instrument on the SOHO spacecraft and process them to remove the p-mode oscillation signal, the axisymmetric flows, the convective blueshift signal, and instrumental artifacts. The remaining Doppler signal contains only non-axisymmetric flow structures. The Doppler signal from the horizontal flows in these structures varies like sin ρ, where ρ is the heliocentric angle from disk center. The Doppler signal from radial flows varies like cos ρ. We fit the center-to-limb variation of the mean squared velocity signal to a straight line in sin2 ρ over the central portion of the disk. The intercept of this line at disk center gives the amplitude of the radial component of the flow. The slope of the line gives the amplitude of the horizontal component. We find that the radial flows for typical supergranules have speeds about 10% that of their associated horizontal flows or about 30 m s−1. The ratio of the radial to horizontal flow speed increases from 9% to about 18% as the size of the structure decreases from > 60 Mm to ∼ 5 Mm. We use data simulations to check these results and find a ratio that increases from 5% to only about 12% over the same range of sizes. These smaller ratios are attributed to an underestimation of the horizontal flow speeds due to the fact that the transverse component of the horizontal flow is not detected by Doppler measurements.
机译：我们通过检查多普勒速度信号的中心到边缘的变化来确定超颗粒流速的径向分量。我们获取使用SOHO航天器上的MDI仪器获得的单个多普勒图像，并对它们进行处理，以去除p型振荡信号，轴对称流，对流蓝移信号和仪器伪像。其余的多普勒信号仅包含非轴对称流动结构。这些结构中来自水平流的多普勒信号像sinρ一样变化，其中ρ是距磁盘中心的日心角。来自径向流的多普勒信号像cosρ一样变化。我们将均方速度信号的中心到边缘的变化拟合到磁盘中心部分的sin2 ρ中的一条直线。该线在圆盘中心的截距给出了流的径向分量的幅度。线的斜率给出了水平分量的幅度。我们发现典型超颗粒的径向流速度约为其相关水平流速度的10％或约30 m s-1 。随着结构尺寸从> 60 Mm减小到〜5 Mm，径向流速与水平流速的比率从9％增加到大约18％。我们使用数据模拟来检查这些结果，并发现在相同大小范围内比率从5％增加到仅约12％。这些较小的比率归因于水平流速度的低估，原因是多普勒测量未检测到水平流的横向分量。

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  • 来源
    《Solar Physics》 |2002年第1期|25-38|共14页
  • 作者

    D.H. Hathaway; J.G. Beck; S. Han; J. Raymond;

  • 作者单位

    NASA/Marshall Space Flight Center;

    Stanford University;

    Tennessee Technological University;

    Tennessee Technological University;

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  • 正文语种 eng
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