| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2004: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
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.
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