Natural Sciences (Astrophysics and Astrononmy)
In current time-distance helioseismology analyses the (phase) travel time is commonly used. However, other than the travel time, there are parameters of the cross-covariance functions of the solar oscillation field that are affected by solar interior structure and dynamics. Including these parameters in helioseismology analyses might improve the analyses. Therefore, here we focus on one such parameter, the amplitude. We formulate a two-parameter fit of the cross-covariance function in the regime where the amplitude and travel-time differences of the cross-covariance function are small, and measure amplitudes as well as travel times in several areas on the Sun. We find that the amplitude of the center-to-annulus cross-covariance function in the quiet Sun shows the supergranulation pattern, although the amplitude is noisier than the travel times; the out-in amplitude difference shows positive correlation with the out-in travel-time difference. We also detect significant amplitude reduction due to sunspots, which is consistent with Liang et al. (2013).
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