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Statistical Study of Solar Acoustic-Mode Power

太阳能声模功率统计研究

基本信息

批准号：
16540222
负责人：
SEKII Takashi
金额：
$ 1.22万
依托单位：
National Astronomical Observatory of Japan
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16540222/
关键词：
Solar Oscillation 太陽

项目摘要

1.We examined correlation between acoustic-mode power using Doppler velocity data from MDI (Michelson Doppler Imager) onboard NASA/ESA spacecraft SOHO. Specifically, the Doppler velocity data were acquired as time-series of spherical-harmonic expansion coefficients. Temporal variation of mode power was calculated by using running windows on the time-series. Correlation coefficients were then calculated, and their distribution was obtained. We established that (1)the effect of mode-leakage, due to the fact that we do not observe the entire surface of the Sun, is small, (2)asymmetric distribution of the correlation coefficients, reported by Roth (2991, ApJ, 559, 1165) is certainly there, though the excess of negative correlation is not as much as Roth had reported, and (3)the distribution function does not depend on frequency difference between modes, which is not consistent with Roth's interpretation that the negative correlation excess is due to mode interaction through internal flow of the Sun. We also found that (4)a random-shuffling of the time-series does not change the distribution function significantly, which implies that the negative correlation excess is due to a process that is steady in the time scale longer than mode damping time.2.We compared the data with results from a simple model of damped harmonic oscillator with a stochastic excitation. In a certain range of parameters, the asymmetry of the distribution of the correlation coefficients and the negative correlation excess can be reproduced. A detailed comparison, which involves even simpler models, is going on.This research was carried out in collaboration with Dr.Heon-Young Chang of Kyungpook National University, South Korea. A joint publication is now in preparation.

1.我们利用NASA/ESA航天器SOHO上的MDI（迈克尔逊多普勒成像仪）的多普勒速度数据检验了声模功率之间的相关性。具体而言，多普勒速度数据以球调和膨胀系数的时间序列形式得到。在时间序列上使用运行窗口计算模式功率的时间变化。然后计算相关系数，得到相关系数的分布。我们确定：(1)由于我们没有观测到太阳的整个表面，模态泄漏的影响很小；(2)Roth （2991, ApJ, 559,1165）报道的相关系数的不对称分布肯定存在，尽管负相关的过量没有Roth报道的那么多；(3)分布函数不依赖于模态之间的频率差。这与Roth的解释不一致，即负相关过剩是由于太阳内部流动的模式相互作用。我们还发现(4)时间序列的随机洗牌不会显著改变分布函数，这意味着负相关过剩是由于一个过程在比模态阻尼时间更长的时间尺度上是稳定的。我们将数据与随机激励下阻尼谐振子的简单模型的结果进行了比较。在一定的参数范围内，可以再现相关系数分布的不对称性和负相关过剩。一项涉及更简单模型的详细比较正在进行中。这项研究是与韩国庆北国立大学的张宪荣博士合作进行的。目前正在编写一份联合出版物。