Sensitivity analysis of the solar rotation to helioseismic data from GONG, GOLF and MDI observations

TL;DR

This study uses high-quality helioseismic data from GONG, GOLF, and MDI to analyze the solar rotation profile, especially in the core, introducing a new inversion method and sensitivity analysis to assess the impact of different mode sets.

Contribution

It presents a novel inversion methodology and a sensitivity analysis framework that links mode set selection to the accuracy of inferring the solar radiative zone rotation, including the core.

Findings

Most of the radiative zone rotates like a solid body.

The solar core appears to slow down compared to the outer radiative zone.

Adding low-frequency and g-modes could improve core rotation estimates.

Abstract

Accurate determination of the rotation rate in the radiative zone of the sun from helioseismic observations requires rotational frequency splittings of exceptional quality as well as reliable inversion techniques. We present here inferences based on mode parameters calculated from 2088-days long MDI, GONG and GOLF time series that were fitted to estimate very low frequency rotational splittings (nu < 1.7 mHz). These low frequency modes provide data of exceptional quality, since the width of the mode peaks is much smaller than the rotational splitting and hence it is much easier to separate the rotational splittings from the effects caused by the finite lifetime and the stochastic excitation of the modes. We also have implemented a new inversion methodology that allows us to infer the rotation rate of the radiative interior from mode sets that span l=1 to 25. Our results are compatible with the sun rotating like a rigid solid in most of the radiative zone and slowing down in the core (R_sun < 0.2). A resolution analysis of the inversion was carried out for the solar rotation inverse problem. This analysis effectively establishes a direct relationship between the mode set included in the inversion and the sensitivity and information content of the resulting inferences. We show that such an approach allows us to determine the effect of adding low frequency and low degree p-modes, high frequency and low degree p-modes, as well as some g-modes on the derived rotation rate in the solar radiative zone, and in particular the solar core. We conclude that the level of uncertainties that is needed to infer the dynamical conditions in the core when only p-modes are included is unlikely to be reached in the near future, and hence sustained efforts are needed towards the detection and characterization of g-modes.