The Solar Acoustic Spectrum and Eigenmode Parameters

Chitre

2010

A&A

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Context. The solar rotation profile is conical rather than cylindrical as it could be expected from classical rotating fluid dynamics (e.g. Taylor-Proudman theorem). Thermal coupling to the tachocline, baroclinic effects and latitudinal transport of heat have been suggested to explain this peculiar state of rotation. Aims. To test the validity of thermal wind balance in the solar convection zone using helioseismic inversions for both the angular velocity and fluctuations in entropy and temperature. Methods. Entropy and temperature fluctuations obtained from 3D hydrodynamical numerical simulations of the solar convection zone are compared with solar profiles obtained from helioseismic inversions. Results. The temperature and entropy fluctuations in 3D numerical simulations have smaller amplitude in the bulk of the solar convection zone than those derived from seismic inversions. Seismic inversion provides variations of temperature from about 1 K at the surface to up to 100 K at the base of the convection zone while in 3D simulations they are of an order of 10 K throughout the convection zone up to 0.96 R . In 3D simulations, baroclinic effects are found to be important to tilt the isocontours of Ω away from a cylindrical profile in most of the convection zone, helped by Reynolds and viscous stresses at some locations. By contrast the baroclinic effect inverted by helioseismology is much larger than what is required to yield the observed angular velocity profile. Conclusions. The solar convection does not appear to be in strict thermal wind balance, Reynolds stresses must play a dominant role in setting not only the equatorial acceleration but also the observed conical angular velocity profile.

“…We use data from GONG (Hill et al 1996) and SOI/MDI (Schou 1999). Each data set consists of mean frequencies of different (n, l) multiplets and the corresponding splitting coefficients.…”

Section: The Helioseismic Data and Inversion Techniquementioning

confidence: 99%

Is the solar convection zone in strict thermal wind balance?

Brun

Chitre

2010

A&A

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“…We use data obtained by the GONG (Hill et al 1996) and MDI (Schou 1999) projects for this work. These data sets consist of the mean frequency and the splitting coefficients of different (n, ) multiplets.…”

Section: Data and Analysismentioning

confidence: 99%

Solar Rotation Rate During the Cycle 24 Minimum in Activity

Basu

2010

ApJ

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The minimum of solar cycle 24 is significantly different from most other minima in terms of its duration as well as its abnormally low levels of activity. Using available helioseismic data that cover epochs from the minimum of cycle 23 to now, we study the differences in the nature of the solar rotation between the minima of cycles 23 and 24. We find that there are significant differences between the rotation rates during the two minima. There are differences in the zonal-flow pattern too. We find that the band of fast rotating region close to the equator bifurcated around 2005 and recombined by 2008. This behavior is different from that during the cycle 23 minimum. By autocorrelating the zonal-flow pattern with a time shift, we find that in terms of solar dynamics, solar cycle 23 lasted for a period of 11.7 years, consistent with the result of Howe et al. (2009). The autocorrelation coefficient also confirms that the zonal-flow pattern penetrates through the convection zone.

“…We have used solar oscillations frequencies obtained by the Global Oscillation Network Group (GONG; Hill et al 1996) as well as those from the Michelson Doppler Imager (MDI; Schou 1999) on board the Solar and Heliospheric Observatory (SOHO). We use 97 sets of frequencies from GONG spanning the period from 1995 May 7 to 2005 January 1.…”

Section: Determining Z In the Solar Convection Zonementioning

confidence: 99%

Determining Solar Abundances Using Helioseismology

Basu

2006

ApJ

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The recent downward revision of solar photospheric abundances of oxygen and other heavy elements has resulted in serious discrepancies between solar models and solar structure as determined through helioseismology. In this work we investigate the possibility of determining the solar heavy-element abundance without reference to spectroscopy by using helioseismic data. Using the dimensionless sound-speed derivative in the solar convection zone, we find that the heavy-element abundance Z ¼ 0:0172 AE 0:002, which is closer to the older, higher value of the abundances.