On the Variation of the Peak Asymmetry of Low‐ℓ Solar<i>p</i>Modes

Jiménez-Reyes, S. J.; Chaplin, W. J.; Elsworth, Y.; García, R. A.; Howe, R.; Socas‐Navarro, H.; Toutain, T.

doi:10.1086/509700

Cited by 51 publications

(42 citation statements)

References 32 publications

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“…It corresponds today to almost 12 yr of continuous measurements, with a duty cycle close to 100%. The response function of the GOLF sodium Fraunhofer line is different between the blue-and the red-wing configurations (Lefebvre et al 2008), with averaged heights in the solar atmosphere of 322 km and 480 km, respectively (Jiménez-Reyes et al 2007). The measurements obtained in the red-wing configuration originate higher up in the solar atmosphere with larger contributions from the chromosphere.…”

Section: Data Setsmentioning

confidence: 99%

Seismic sensitivity to sub-surface solar activity from 18 yr of GOLF/SoHO observations

Salabert

García

Turck‐Chièze

2015

A&A

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Solar activity has significantly changed over the last two Schwabe cycles. After a long and deep minimum at the end of Cycle 23, the weaker activity of Cycle 24 contrasts with the previous cycles. In this work, the response of the solar acoustic oscillations to solar activity is used in order to provide insights into the structural and magnetic changes in the sub-surface layers of the Sun during this on-going unusual period of low activity. We analyze 18 yr of continuous observations of the solar acoustic oscillations collected by the Sun-as-a-star GOLF instrument on board the SoHO spacecraft. From the fitted mode frequencies, the temporal variability of the frequency shifts of the radial, dipolar, and quadrupolar modes are studied for different frequency ranges that are sensitive to different layers in the solar sub-surface interior. The low-frequency modes show nearly unchanged frequency shifts between Cycles 23 and 24, with a time evolving signature of the quasi-biennial oscillation, which is particularly visible for the quadrupole component revealing the presence of a complex magnetic structure. The modes at higher frequencies show frequency shifts that are 30% smaller during Cycle 24, which is in agreement with the decrease observed in the surface activity between Cycles 23 and 24. The analysis of 18 yr of GOLF oscillations indicates that the structural and magnetic changes responsible for the frequency shifts remained comparable between Cycle 23 and Cycle 24 in the deeper sub-surface layers below 1400 km as revealed by the low-frequency modes. The frequency shifts of the higher-frequency modes, sensitive to shallower regions, show that Cycle 24 is magnetically weaker in the upper layers of Sun.

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Section: Data Setsmentioning

confidence: 99%

Seismic sensitivity to sub-surface solar activity from 18 yr of GOLF/SoHO observations

Salabert

García

Turck‐Chièze

2015

A&A

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“…The nominal height of observation is at ≈260 km above the photosphere (e.g. Jiménez-Reyes et al 2007). We analyzed the data provided by BiSON instruments from 11 April 1996 to 4 April 2009.…”

Section: Sun-as-a-star Observations From Ground Based Networkmentioning

confidence: 99%

The quasi-biennial periodicity (QBP) in velocity and intensity helioseismic observations

Simoniello

Finsterle

Salabert

et al. 2012

A&A

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Aims. We looked for signatures of quasi-biennial periodicity (QBP) over different phases of solar cycle by means of acoustic modes of oscillation. Low-degree p-mode frequencies are shown to be sensitive to changes in magnetic activity due to the global dynamo. Recently there has been reported evidence of two-year variations in p-mode frequencies. Methods. Long high-quality helioseismic data are provided by BiSON (Birmingham Solar Oscillation Network), GONG (Global Oscillation Network Group), GOLF (Global Oscillation at Low Frequency) and VIRGO (Variability of Solar IRradiance and Gravity Oscillation) instruments. We determined the solar cycle changes in p-mode frequencies for spherical degree = 0, 1, 2 with their azimuthal components in the frequency range 2.5 mHz ≤ ν ≤ 3.5 mHz. Results. We found signatures of QBP at all levels of solar activity in the modes more sensitive to higher latitudes. The signal strength increases with latitude and the equatorial component also seems to be modulated by the 11-year envelope. Conclusions. The persistent nature of the seismic QBP is not observed in the surface activity indices, where mid-term variations are found only from time to time and mainly in periods of high activity. This feature, together with the latitudinal dependence, provides more evidence of a mechanism that is almost independent and different from the one that brings the active regions up to the surface. Therefore, these findings can be used to provide more constraints on dynamo models that consider a further cyclic component on top of the 11-year cycle.

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“…The nominal height in the solar atmosphere at which the measurement is made is ≈260 km above the photosphere (e.g. Jiménez-Reyes et al 2007) as defined by τ = 1 at 500nm . The data provided by the BiSON network for this investigation cover the period from April 1996 until July 2006.…”

Section: Ground-based Networkmentioning

confidence: 99%

“…Due to the malfunctioning of the polarization system, GOLF is working in single-wing configuration, which has changed during the 10 years of observations as follows: 1) 1996-1998 in the blue-wing configuration; 2) 1998-2002 in the red-wing configuration; 3) 2002 until today in the blue-wing configuration (Ulrich et al 2000;García et al 2005). Due to the formation heights of the spectral lines GOLF observes at ≈330 km in the blue-wing configuration, but at ≈ 480 km in the red-wing configuration (Jiménez-Reyes et al 2007). For this survey we will use only the first blue-wing period together with the red-wing.…”

Section: Satellite Instrumentsmentioning

confidence: 99%

Acoustic power absorption and enhancement generated by slow and fast MHD waves

Simoniello¹,

Finsterle²,

García³

et al. 2010

A&A

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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 < ν < 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 < ν < 4.5 mHz with a maximum suppression for frequencies in the range between 2.5 mHz < ν < 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 < ν < 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 < ν < 6.8 mHz, we found an enhancement in the velocity amplitudes with the maximum 36 ± 7 per cent occurring for 6.3 mHz < ν < 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.

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On the Variation of the Peak Asymmetry of Low‐ℓ SolarpModes

Cited by 51 publications

References 32 publications

Seismic sensitivity to sub-surface solar activity from 18 yr of GOLF/SoHO observations

Seismic sensitivity to sub-surface solar activity from 18 yr of GOLF/SoHO observations

The quasi-biennial periodicity (QBP) in velocity and intensity helioseismic observations

Acoustic power absorption and enhancement generated by slow and fast MHD waves

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