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Astron. Astrophys. 329, 1119-1124 (1998)

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Solar activity cycle frequency shifts of low-degree p-modes

S.J. Jiménez-Reyes, C. Régulo, P.L. Pallé and T. Roca Cortés

Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain

Received 25 March 1997 / Accepted 6 August 1997


We report on an extensive analysis of the low-degree p -mode frequency shifts over Solar Cycle n [FORMULA] 22 (1984-1995) based on continuous data taken at the Observatorio del Teide (Tenerife). Aside from the known good correlation between frequency shifts and solar activity indices, we have also investigated on short and long time-scales correlations (from 2 months to 1.5 years and from 1.5 to 11 years) showing different behavior. In addition, by using smoothed data for both, frequency shifts and solar activity indices, a "hysteresis" phenomenon is observed. This implies different behavior of both quantities in the ascending and descending parts of the cycle, while saturation effects exists at extreme phases. Finally, a degree dependence of this behavior is also noticed when analyzing separately the shifts for the even (0, 2) and odd (1, 3) mode groups. These results show that the p -mode frequency shifts are very sensitive to structural changes taking place in the Sun as the solar activity cycle proceeds; either in their upper layers, as activity migrates towards the equator, or, in its interior with a phenomenon that slowly progresses outwards, or both. A much more complete picture should emerge when data obtained from the new operational helioseismic projects over more than one solar cycle come into existence.

Key words: Sun: activity – Sun: general – Sun: interior – Sun: oscillations

Send offprint requests to: P.L. Pallé

© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997