Computer Science – Sound
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp21c06r&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SP21C-06 INVITED
Computer Science
Sound
7522 Helioseismology
Scientific paper
Some of the most exciting results that the field of helioseismology has provided in recent years have come from numerical inversions of different properties of the solar p-mode oscillations. Such inversions have been primarily of three types: 1) structural inversions which have employed tables of the frequencies of various p-modes and their associated uncertainties to infer different thermodynamic properties of the solar interior as functions of radius and latitude, 2) rotational inversions which have employed tables of the frequency splittings of the modes of different azimuthal order to measure the internal angular velocity as functions of radius and latitude, and 3) horizontal flow inversions which have employed sets of frequencies of the rings that are observed in three-dimensional power spectra to infer sub-photospheric horizontal flow vectors as functions of depth, latitude and longitude. Unfortunately, the vast majority of such inversions have only included frequencies or frequency splittings of the low- and the intermediate-degree oscillations. Furthermore, the horizontal flow inversions have been somewhat limited by the difficulties in accurately fitting the rings of the higher-degree power spectra. These limitations have prevented helioseismologists from accurately inferring the sound speed, density, adiabatic gradient, and helium abundance in the outermost three to four percent (by radius) of the solar interior. In addition, the absence of high-l frequency splittings from most past rotational inversions has limited the accuracy with which we have been able to estimate the angular velocity of the solar surface layers. These limitations have mainly come about because for l>= 200 the individual modal peaks blend together into broad ridges of power. Fitting such ridges requires knowledge of the amount of power which leaks into the sidelobes that are adjacent to the true spectral peaks. Such leakage information requires detailed knowledge of the spatial behavior of each different intrument, of the ratio of horizontal and vertical components of the solar p-mode eigenfunctions, and of the temporal window function of each dataset. In this presentation we will demonstrate the high-l frequencies which we have obtained from a new fitting technique which employs m-averaged power spectra, temporal window functions, and spatial leakage matrices to fit each mode or ridge with a total of seven peaks. We will also demonstrate that we have obtained evidence from the fitting of GONG power spectra that the true ratios of the eigenfunction components match the theoretical predictions of these ratios. Finally, we will also demonstrate that cross-correlations of the peaks and ridges in the 2l+1 individual spectra at each l result in systematic jumps in the frequency-splitting coefficients for l>=200 due to the blending of the peaks into ridges. We will point out that, unless some method can be found which overcomes these detrimental effects of peak-blending, we will not be able to provide measures of the latitudinal behavior of the solar angular velocity close to the photosphere which will be independent of the horizontal flow mesurements obtained with the so-called ``ring and trumpet'' technique.
Kosovichev Aleksandr G.
Reiter Johann
Rhodes Elmer J.
Scherrer Philip H.
Schou Jepser
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