It is broadly believed now that p-modes are excited stochastically, and then intrinsically dumped. But the basic features of the excitation processes should be revealed from the experiments.
Many questions arise when we try to describe the excitation processes using an experimental information. What is the distribution of the energy among the modes of different frequencies (radial orders) as well as different spherical degrees l? What is the rate of p-mode excitation? In other words, how many events of the mode excitation with an amplitude above some level one could be expected during given time interval? Does this rate depend on the degree of the mode and/or its frequency? Is the excitation rate more or less constant in time or there are intervals of the low and high excitation activity? If so, how they are connected with other manifestations of solar activity? And so on.
On the other side, the answers on the questions mentioned above could provide some hints to interpret the properties of the obtained line profiles and to find the best possible way to reveal their characteristics (frequencies, amplitudes, linewidths and rotational splitting) from the available data.
The fitting of the erratic power spectra of the oscillations measurements by the theoretically expected line profiles is generally used for this purpose.
But there is a weak point in any technique of this kind --- one has to make a hypothesis about the shape of the fit of the experimental data power spectrum.
Recently we have successfully applied a modification of the standard Fourier transform, named Fourier Power Averaging -- FPA, to the analysis of IPHIR (V.Gavryusev & E.Gavryuseva,1994, 1995) and IRIS data (the paper is under preparation now). This technique permits to get an approximation to the mode line profile without any fitting and, consequently, without any a priori hypothesis about its shape. The obtained line profiles for low l solar p-modes manifest two kinds of asymmetries - the amplitude asymmetry of the different components of the rotationally splitted multiplets and the asymmetry of the component shape. The first kind of asymmetry is, probably, the result of some difference in the time behavior of the components in the multiplet.
We are working already for some time on the investigation of the time behavior of the p-mode line profiles in IPHIR and IRIS data. It is already follows from our results, as well as from the results of other authors (see, for example, F.Baudin, 1995) that there is a possibility to select time intervals of the strong excitation of the modes. Hence one can try to investigate their statistical properties directly.
We would like to put our efforts in the frame of SOI project on the next topics:
Practically all necessary software is already in use; but some modifications have to be done to adapt to SOI data.
We are open for collaboration with everyone who is interested in the same topics, which are obviously of common interest.
[1995]
Gavryusev V., Gavryuseva E., 1995, in SOHO 95, in publication
1995]
Gavryusev V., Gavryuseva E., 1995, A&A, submitted
[1995] Baudin F., 1995, in GONG 94: Helio-- and Astero--Seismology from the Earth and Space, ed. R.K.Ulrich, E.J.Rhodes, Jr., W.Däppen, ASP Conference Series, v. 76, 475