Search Publications
The acoustic cutoff frequency of the Sun and the solar cycle
García, R. A.; Pallé, P. L.; Jiménez, A.
The acoustic cutoff frequency - highest frequency for acoustic solar eigenmodes-is an important parameter of the solar atmosphere because it determines the upper boundary of the p mode cavities. At frequencies beyond this value, acoustic disturbances are no longer trapped waves but traveling waves. Interferences amongst them, originate higher freq…
The dynamics of the radiative zone of the Sun
Mathis, S.; Turck-Chièze, S.; Piau, L. +4 more
Helioseismology puts strong constraints on the internal sound speed and on the rotation profile in the radiative zone. Young stars of solar type are more active and faster rotators than the Sun. So we begin to build models which include different rotation histories and compare the results with all the solar observations. The profiles of the rotati…
Zonal Flows Throughout Cycle 23
Basu, Sarbani; Antia, H. M.
We use available GONG and MDI data to study how solar zonal flows evolved over cycle 23 and whether or not there were differences between the minima of cycles 23 and 24. An autocorrelation study shows that as far as the zonal-flows are concerned, cycle 23 lasted for about 11.7 years, considerably shorter than what is seen from magnetic indices. We…
Wave absorption and moat flow in AR9787
Thompson, M. J.; Roth, M.
We present the results of a study of the wave absorption and the moat flow around the sunspot in AR9787 (the "HELAS sunspot", so-called because it has been the object of in-depth study at a HELAS workshop) using Fourier-Hankel decomposition of the oscillatory wave field. We carry out inversions both for the flow speed and for the sound speed pertu…
Mode visibilities in radial velocity and intensity Sun-as-a-star helioseismic measurements
García, R. A.; Ballot, J.; Salabert, D.
We analyze more than 5000 days of Sun-as-a-star radial velocity GOLF and intensity VIRGO observations to measure the visibilities of the I = 0, 1, 2, and 3 modes and the m-amplitude ratios of the I = 2 and 3 modes in the solar acoustic spectrum. We provide observational values that we compare to theoretical predictions.
Variation in the frequency separations with activity and impact on stellar parameter determination
García, R. A.; Creevey, O. L.; Salabert, D.
Frequency separations used to infer global properties of stars through asteroseismology can change depending on the strength and at what epoch of the stellar cycle the p-mode frequencies are measured. In the Sun these variations have been seen, even though the Sun is a low-activity star. In this paper, we discuss these variations and their impact …
Preliminary velocity flows inside NOA AR 10720 derived by temporally evolving ring diagram analysis of SOHO/MDI dopplergrams
Pintér, Balázs; Burrows, Keiran
Between 13th and 16th January 2005, NOA active region 10720 was the site of several large flares, one of which induced a solar quake. The expanding wave front of the quake was visible across the surface, causing both horizontal and vertical plasma displacements. Using a new temporal scanning technique for ring diagram analysis of SOHO/MDI (Michels…
Accurate Mapping of the Torsional Oscillations: a Trade-Off Study between Time Resolution and Mode Characterization Precision
Eff-Darwich, A.; Korzennik, S. G.
One salient result of global helioseismology is the mapping of the so-called torsional oscillations below the solar surface. These subsurface flows are inferred by inverting rotational frequency splitting sets of global modes. These flows extend down to a depth of at least 0.8 R, and are likely associated with the activity cycle of our star. To be…
The solar core as never seen before
Eff-Darwich, A.; Korzennik, S. G.
One of the main drawbacks in the analysis of the dynamics of the solar core comes from the lack of consistent data sets that cover the low and intermediate degree range (ell = 1,200). It is usually necessary to merge data obtained from different instruments and/or fitting methodologies and hence one introduces undesired systematic errors. In contr…
Low frequency signal in the GOLF measurements
Provost, J.; Grec, G.; Renaud, C.
This paper shows the results obtained using a revisited method to normalize the velocity evaluation extracted from the measurements, for roughly 14 years of GOLF data. For the search of g modes, we calculate the low frequency power spectrum of the signal with 2 different approaches: • The classical calculation of the power spectrum of the velocity…