Helioseismic estimation of convective overshoot in the Sun
Helioseismic estimation of convective overshoot in the Sun
复制标题
太阳对流超调的日震估计
DOI：
10.1093/mnras/276.1.283
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
M. Thompson
中科院分区：
文献类型：
--
作者：
J. Christensen;M. Monteiro;M. Monteiro;M. Thompson
Monteiro、Christensen-Dalsgaard和Thompson利用太阳对流带底部的振荡频率中存在的周期信号，给出了太阳对流超射层的上限。其他研究表明，这可能是不可能的，因为信号的幅度不随层的范围单调变化。在这项工作中，使用了一套新的更完整的模型来比较信号拟合得到的幅度与预期幅度的值。它们是通过假设在对流区底部发生的快速变化并产生周期信号可以描述为声速导数的不连续来确定的。因此，由于声速的三阶导数的不连续而产生的信号幅度与辐射梯度的导数成正比，而由二阶导数的不连续产生的幅度与发生转变的位置处的辐射梯度和绝热梯度之间的差成正比。后者只有在存在超调的情况下才是非零的。对p模频率中信号幅度的渐近预测与从具有大量超调区域的拟合模型中找到的值很好地一致；正如Monteiro等人也发现的那样，观测到的太阳频率对这种性质的超调的程度施加了严格的限制。
By using the periodic signal present in the frequencies of oscillation due to the base of the solar convection zone, Monteiro, Christensen-Dalsgaard & Thompson gave an upper limit to the extent of a layer of convective overshooting in the Sun. Alternative studies have suggested that it may not be possible to do so since the amplitude of the signal does not vary monotonically with the extent of the layer.In this work a new more complete set of models is used to compare the values of the amplitude obtained from the fitting of the signal with the expected amplitudes. These are determined using the assumption that the rapid variation occurring at the base of the convection zone and creating the periodic signal can be described as discontinuities of the sound-speed derivatives. The amplitude of the signal due to the discontinuity of the third derivative of the sound speed is then proportional to the derivative of the radiative gradient, while the amplitude resulting from the discontinuity of the second derivative is proportional to the difference between radiative and adiabatic gradients at the position where the transition occurs. The latter is non-zero only if overshoot is present.Asymptotic predictions of the amplitudes of the signal in the p-mode frequencies are in good agreement with the values found from fitting models with substantial overshoot regions; as was also found by Monteiro et al., the observed solar frequencies place severe limits on the extent of overshoot of this nature.