Rossby vortices excited near the base of the solar convection zone are very appealing objects for interpretation of a number of solar phenomena such as long-lived large-scale magnetic structures, the poleward drift of the axisymmetric components after the polar field reversal, and a peculiar long-term behavior of the nonaxisymmetric components (Tikhomolov and Mordvinov 1996).

The overlap of peaks of split multiplets in oscillation power spectra and the leakage of other degree modes could significantly affect the measurements of the rotational frequency splitting. We have developed optimal masks which allow to isolate individual components of the multiplets. The method is applied to the Michelson Doppler Imager Low-l data. The results of the mode frequency measurements are reported.

Recently the LOWL Group has made available 2-year averages of frequency splitting data obtained mainly for low values of the degree ℓ. Charbonneau et al. (1997) find a nearly flat rotational curve in the deep radiative core from these data using a Genetic Forward Modeling method. Subsequently, they test the assumption of latitude independence for r < 0.5 by performing a 1.5-D inversion, and find a rotation rate which is 25% greater at the pole than at the equator for 0.1 < r < 0.2.

We made simultaneous high resolution observations of the solar granular field and the Sun‘s seismic events. We find that these events occur in the dark intergranular lanes. The events are preceded by the darkening of an already dark lane. On the leading edge of each event, there is a second more abrupt and precipitous darkening lasting a minute or two.

Solar flares are the strongest localized seismic disturbances on the solar surface. During the impulsive phase a high-energy electron beam heats the chromosphere, resulting in explosive evaporation of chromospheric plasma at supersonic velocities. This upward motion is balanced by a downward recoil in the lower part of the chromosphere that excites propagating waves in the solar interior. On the solar surface the outgoing circular flare waves resemble ripples from a pebble thrown into a pond. We report on first observations of the seismic effects of a solar flare from the SOHO Michelson Doppler Imager (MDI) and compare the results with a theoretical model. Observation of flare seismic waves provide important information about the flare mechanism and about the subphotospheric structure of active regions.

In his opening address at the conference Dr. Tim Brown posed the line asymmetry problem between velocity and intensity as a puzzle in helioseismology that has been resisting theoretical explanation for many years. It was the observations of Duvall et al. (1993) that for the first time indicated that the power spectrum of solar acoustic modes show varying amounts of asymmetry. In particular, the velocity and intensity power spectra revealed an opposite sense of asymmetry. Many doubted the correctness of the experiment and thought it to be a puzzling result (Abrams & Kumar, 1996). Many authors have investigated this problem theoretically and have found that there is an inherent asymmetry whenever there is a localized source exciting the solar oscillations (Gabriel, 1995; Roxburgh & Vorontsov, 1995; Abrams & Kumar, 1996; Nigam et al. 1997). This problem has important implications in helioseismology where the eigenfrequencies are generally determined by assuming that the power spectrum was symmetric and can be fitted by a Lorentzian. This leads to systematic errors in the determination of frequencies and, thus, affects the results of inversions (Rhodes et al. 1997). In this paper we offer an explanation for the difference in parity of the two asymmetries and estimate the depth and type of the sources that are responsible for exciting the solar p-modes.

Millions of seismic eigenmodes are excited to low amplitudes in the Sun, with an amplitude spectrum that grows approximately as a power of the frequency until it reaches a maximum at 3 mHz, and then drops off again towards higher frequencies (Libbrecht, 1988; Libbrecht & Woodard, 1991).

According to observational data some regions of quiet sun show an excess, or the “emission” of acoustic waves. We propose a mechanism to explain the excess of the emission of acoustic waves based on nonlinear coupling of magnetic flux tube oscillations and the acoustic waves. We also suggest a new approach in the data analysis, which can be called “Raman spectroscopy of p-modes”. This new idea is based on the fact that oscillating flux tubes constructively interfere with the acoustic wave which results in the generation of beat waves with combinational frequencies: the power spectra of scattered waves in addition to main peak will have Stokes and anti-Stokes satellites. Their amplitude and frequency shift reflect the properties and the structure of the observed region.

Currently, the most successful direct simulation of the solar granules (and the convection/radiation transition layer) is the three-dimensional (3D) model computed by Stein and Nordlund (1989). So far, there is no other similar 3D models available for comparison [however, see Ludwig et al. (1997) for a recent 2D calculation]. We are developing an alternative numerical approach to simulate the 3D radiation hydrodynamics of this layer. In this approach, the Eddington approximation is used to handle the radiation rather than solving the radiative transfer equations along rays, and the ADISM method (Chan and Wolff 1982) which solves the Navier Stokes equations in conservative forms is used to speed up the thermal relaxation of the fluid layer. We are in the process of testing the numerical accuracy of the codes. This paper summarizes the results of a test that illustrate the effects of vertical space resolution on the mean profiles of some important quantities.

Recently, Chang et al. (1997, hereafter Paper I) developed a new method, based on time-distance curves (Duvall et al. 1993), to construct a three-dimensional acoustic intensity image of the solar interior. Here we report results from another data set.

Solar p-mode waves, which are continually generated and dissipated stochastically by the turbulent convection, are scattered and absorbed by local inhomogeneities. If we appropriately add p-mode waves observed at the surface, based on the knowledge of how the waves propagate (time-distance curves), such that acoustic signals emanating from a particular point at a particular time are collected in phase, we can reconstruct the p-mode amplitude at the target point at the target time. The scheme of adding signals from a target point in phase plays the same role as a lens in optics. Thus we call it the “computational acoustic lens” (Paper I). This imaging technique can be used to construct acoustic amplitudes at any point in the solar interior based on the time-distance curve between that depth and the surface, which can be computed from a standard solar model based on the ray theory. The time series of constructed a plitudes provides information of both the intensity and the phase of the wavetrain. The intensity can be used to study p-mode absorption regions, and the phase can be used to probe other properties of local inhomogeneities, such as flow and change in wave speed.

BiSON is a 6-station, world-wide network of instruments which observe low-degree solar oscillations.

Theory (Goldreich & Keeley, 1977) predicts that the probability distribution of the mode powers is expected to follow negative exponential statistics under the condition that the interval of time for which the modes are averaged is less than the lifetime of the mode. Simulations (Chaplin et al, 1997) confirm this. The first publication of such an analysis for real data (Elsworth et al., 1995) showed that the oscillations largely follow the predictions with a small excess of the very largest power in the modes. In this paper we extend the previous observations of BiSON data to 80 months of data taken during the declining phase of the solar cycle. The data span the period January 1990 to August 1996. The data have been analysed using Fourier transforms each about 1/2 day in length. The minimum data fill accepted in any one period was 0.7 (Elsworth et al, 1995). Below this fill the data were discarded. The resolution of such short transforms is insufficient to distinguish between the components of the even and odd mode pairs. The mode powers are calculated for mode pairs ℓ = 0 & 2 and ℓ=1&3.

Comparison with theoretical predictions show that, as seen previously, there is still an excess of very high excitations which can be seen throughout the 80 months.

We have studied the statistical properties of the energy of individual p modes, extracted from 310 days of GOLF data near the solar minimum. The exponential distribution of the energy of each mode is clearly seen. The modes are found to be uncorrelated with a ±0.6% accuracy, thus supporting the hypothesis of stochastic excitation by the solar convection.

The same analysis performed on the same modes just before the solar maximum, using IPHIR data, rejects the hypothesis of no correlation at a 99.3% confidence level. A simple model suggests that 31.3 ± 9.4% of the energy of each mode is coherent among the modes studied in IPHIR data, corresponding to a mean correlation of 10.7 ± 5.9%.

The secondary objective of the GOLF experiment on-board the SOHO space mission is to measure the line-of-sight component of the disk averaged magnetic field of the Sun. GOLF is an improved disk-integrated sunlight resonant scattering spectrophotometer. Using an extra fixed quarter wave plate placed at the entrance of the instrument, enables a selection of the circularly polarized solar light and therefore, the disk averaged solar line-of-sight component of the magnetic field can be obtained. Unfortunately, due to occasional malfunction of the rotating mechanisms, only a series of 26 continuous days are available. Here, the analysis of this series is presented including the value of the averaged magnetic field.

We used the measurements of solar oscillations taken by GONG and GOLF experiments. The first set of data are the integrated images obtained from the complex GONG observations taken from June 10 of 1995 to January 7 of 1997, 578 days in total, referenced below as ts0 time series. Radial, dipole and quadrupole modes are well visible in this time series. The second data set is the GOLF time series obtained on-board SOHO mission from April 11, 1996 to June 22, 1997. GOLF observes the “Sun as a star”. This time series is similar to ts0 of GONG but of a better quality (better signal-to-noise ratio; uniform, practically uninterrupted data). Both experiments are significantly overlapped in time. Because of this the direct comparison between them is possible, and the effects visible in both observations support each other.

We address the problem of the opposite asymmetry of low-frequency p-mode line profiles observed in intensity and velocity measurements (Duvall et al. 1993). We use a simple model to illustrate that this feature can be explained by including a contribution from the stochastic excitation velocity field to the non-resonant background in the doppler measurements.

The day before the start of IAU Symposium 185 Wojtek Dziembowski and I were sitting in the beautiful 300-year-old garden of Shisendo in Kyoto discussing asteroseismology. Wojtek put his fingertips together to make a little temple of his hands in front of him. Then, slowly moving this temple up and down in front of him, while staring off at the green Japanese mosses in the dappled sun and shade of Shisendo‘s garden forest he said to me in his studied way, “Don, I am not sure that there is any asteroseismology yet”. I thought, “Uh-oh. If others believe that is true, then they may not think I have much to say in my review of new developments in asteroseismology at S185.” Yet I do have much to say, so I think I had better define what I mean by asteroseismology.

Asteroseismology depends on the ability to determine frequencies for identified modes of stellar oscillation, and to use these frequencies to probe stellar interiors. Thus crucial aspects are the dependence of the frequencies on stellar properties, and the likelihood that modes are excited to observable amplitudes. I provide a brief overview of these issues and some remarks about how the frequencies may be analyzed, as a background for the more detailed presentations elsewhere in the proceedings.

The pulsations of white dwarf stars are potentially a rich source of information about white dwarf structural properties. Extracting and applying this information to improve our knowledge of white dwarf interiors requires measuring individual eigenperiods in a complex power spectrum, and identifying the character of the eigenmodes they represent. This review will summarize observational progress in these areas for the ZZ Ceti pulsators.

The development of helioseismology as a forefront area of solar and stellar astronomy has been fascinating to watch. Helioseismology takes full advantage of the benefits of lots of photons and a spatially resolved target. These allow measurement of tiny amplitude photospheric velocity and flux variations, and the precise identification of the oscillation modes corresponding to each observed frequency.

Warning to the unsuspecting reader: The editors of this volume have (bravely) asked me to “preserve the spirit” of my oral presentation. It is difficult to translate the stirring grandeur of a multi-coloured flashing bowtie into mere words and diagrams. Failing to evoke that grandeur, I have instead settled for occasionally capturing the tackiness of my battery-operated talk in Kyoto.