J. Patrón

Meridional Flows from Ring Diagram Analysis

In order to search for meridional circulation in the solar envelope, we have applied ring diagram analysis to a set of small regions over the surface. The helioseismic data consist of Solar Oscillation Investigation/Michelson Doppler Imager Dopplergrams taken over a time span of about 50 hr (~3000 images) on 1998 June 20-22. The regions studied cover 115° in latitude centered on the equator and 30° in longitude. We find poleward flows between r/ R=0.97 and the surface. There is no evidence in this depth range for the return path of these meridional flows. The temporal stability of these flows will be discussed after the analysis of a synoptic map obtained using the same technique.

Comparison of Two Fitting Methods for Ring Diagram Analysis of Very High l Solar Oscillations

A new method of fitting tridimensional power spectra of solar oscillations is described and compared with a previous one whose use has been more common. The new method fits the parameters of the Lorentzian profiles in a bidimensional k - ω diagram constructed from an azimuthal average of the tridimensional one. The horizontal velocities are then determined keeping these parameters fixed, greatly reducing the computation time. Both methods are compared for two radial orders (n = 3, 4) of a tridimensional power spectrum obtained for a region of about 15° square around solar disk center. The images used in this work correspond to a 3 day set of 1080 × 1080 pixel intensity images obtained at the Observatorio del Teide on 1994 November 8-10 with the Taiwanese Oscillation Network (TON) instrument. The results of the fitted velocities agree within the estimated errors for the two methods. The reduction of the computing time obtained with the new method makes it convenient for the ring diagram analysis.

Time Evolution of Horizontal Subsurface Flows in the Sun

A ring-diagram analysis technique has been applied to a region of the Sun of about 15 deg2 area close to the disk center at dates chosen for several solar rotations in 1996: April 5, May 1, May 28, June 27, July 23, August 20, August 21, and September 18. The horizontal velocity flows inferred directly beneath the solar surface have thus been obtained for the same region of the Sun at the given dates. The data have been obtained at the Observatorio del Teide and the Tashkent stations with the Taiwan Oscillation Network (TON), consisting of 1080 × 1080 pixel Ca II K-line intensity images. The stability of the results, the stability of the method, and the possible temporal evolution of the subsurface flows have been studied from the results. A rotation curve for the differential radial solar rotation down to the first 27 Mm of depth at the equator is also suggested and qualitatively compared to results obtained by other authors.

On the Reliability of Ring Diagram Analysis

A comparison between the results of applying a ring diagram analysis to two data sets is described in order to check the quality of the two sets and the reliability of the method. The series used have been obtained with two different helioseismological instruments with the same spatial resolution. A section of 30 × 30 deg2 about the disk center has been tracked during 512 minutes over a series of images taken simultaneously by the Taiwan Oscillation Network instrument station at the Observatorio del Teide and the Michelson Doppler Imager on board the Solar and Heliospheric Observatory. Three-dimensional power spectra have been constructed from both series and fitted to get horizontal velocity flows as a function of frequency. Finally, an inversion process has been applied to obtain the depth dependence of the average velocity vector in a depth range of 0-25 Mm below the solar surface. The results show an acceptable correlation between the velocities obtained from the fitting of the spectra of both data sets in spite of the different kinds of noise affecting the two instruments. However, the correlation drops when comparing the velocities obtained after the inversion process based on these results.