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Paper: Frequency Shifts of the Individual Low-Degree P-Modes during Solar Cycle 23 and its Extended Minimum
Volume: 428, SOHO-23: Understanding a Peculiar Solar Minimum
Page: 51
Authors: Salabert, D.; García, R. A.; Pallé, P. L.; Jiménez-Reyes, S. J.
Abstract: We study the response of the low-degree solar p-mode frequencies to the unusual extension of the minimum of solar surface activity since 2007. Helioseismic observations collected by the space-based, Sun-as-a-star GOLF instrument and by the ground-based, multi-site network GONG (integrated signal) are analyzed. Temporal variations of the low-degree (l=0,1,2), p-mode frequencies are obtained. Although the known correlation of the frequency changes with solar surface activity is recovered for the period 1996–2007, since the second half of 2007 and until July 2009 (the latest period analyzed) we notice a peculiar behavior amongst modes of different angular degrees. In particular, a clear increase of the l=0 and l=2 p-mode frequencies is obtained consistently since late 2007, while the l=1 frequencies follow the general decreasing trend of surface activity. We interpret these differences in the frequency shifts of individual low-degree modes as indicative of variations at high latitudes in the magnetic flux beneath the surface of the Sun related to the onset of solar cycle 24.
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