Volume 516, June-July 2010
|Number of page(s)||10|
|Published online||22 June 2010|
Acoustic power absorption and enhancement generated by slow and fast MHD waves
Evidence of solar cycle velocity/intensity amplitude changes consistent with the mode conversion theory
PMOD/WRC Physikalisch-Meteorologisches Observatorium Davos-World Radiation Center, 7260 Davos Dorf, Switzerland e-mail: [rosaria.simoniello;wolfgang.finsterle]@pmodwrc.ch
2 Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; CEA, IRFU, SAp, centre de Saclay, 91191 Gif-sur-Yvette, France
3 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot; 5 place Jules Janssen, 92190 Meudon, France e-mail: email@example.com
4 IAC, Instituto de Astrofisíca de Canarias, 38205 La Laguna, Tenerife, Spain
5 Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain e-mail: [salabert;ajm]@iac.es
6 School of Physics and Astronomy, University of Birmingham, Edgbaston, B15 2TT Birmingham, UK e-mail: firstname.lastname@example.org
7 Max-Planck-Institute for Solar System Research, Max-Planck-Strasse 2, 37197 Katlenburg-Lindau, Germany e-mail: email@example.com
Accepted: 1 March 2010
We used long duration, high quality, unresolved (Sun-as-a star) observations collected by the ground based network BiSON and by the instruments GOLF and VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related changes in mode characteristics in velocity and continuum intensity for the frequency range between 2.5 mHz 6.8 mHz. Over the ascending phase of solar cycle 23 we found a suppression in the p-mode amplitudes both in the velocity and intensity data between 2.5 mHz 4.5 mHz with a maximum suppression for frequencies in the range between 2.5 mHz 3.5 mHz. The size of the amplitude suppression is 13 ± 2 per cent for the velocity and 9 ± 2 per cent for the intensity observations. Over the range of 4.5 mHz 5.5 mHz the findings hint within the errors to a null change both in the velocity and intensity amplitudes. At still higher frequencies, in the so called High-frequency Interference Peaks (HIPs) between 5.8 mHz 6.8 mHz, we found an enhancement in the velocity amplitudes with the maximum 36 ± 7 per cent occurring for 6.3 mHz 6.8 mHz. However, in intensity observations we found a rather smaller enhancement of about 5 ± 2 per cent in the same interval. There is evidence that the frequency dependence of solar-cycle velocity amplitude changes is consistent with the theory behind the mode conversion of acoustic waves in a non-vertical magnetic field, but there are some problems with the intensity data, which may be due to the height in the solar atmosphere at which the VIRGO data are taken.
Key words: Sun: oscillations / Sun: surface magnetism / methods: observational / methods: data analysis
© ESO, 2010
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