Improved Helioseismic Analysis of Medium-l Data from the Michelson Doppler Imager

Abstract

We present a comprehensive study of one method for measuring various parameters of global modes of oscillation of the Sun. Using velocity data taken by the Michelson Doppler Imager (MDI), we analyze spherical harmonic degrees l <= 300. Both current and historical methodologies are explained, and the various differences between the two are investigated to determine their effects on global-mode parameters and systematic errors in the analysis. These differences include a number of geometric corrections made during spherical harmonic decomposition; updated routines for generating window functions, detrending timeseries, and filling gaps; and consideration of physical effects such as mode profile asymmetry, horizontal displacement at the solar surface, and distortion of eigenfunctions by differential rotation. We apply these changes one by one to three years of data, and then reanalyze the entire MDI mission applying all of them, using both the original 72-day long timeseries and 360-day long timeseries. We find significant changes in mode parameters, both as a result of the various changes to the processing, as well as between the 72-day and 360-day analyses. We find reduced residuals of inversions for internal rotation, but seeming artifacts remain, such as the peak in the rotation rate near the surface at high latitudes. An annual periodicity in the f-mode frequencies is also investigated.

40 pages, 20 figures. Accepted for publication in Solar Physics. For more information, see http://jsoc.stanford.edu/MDI/MDI_Global.html

References in corpus (2)

• What have we learned from helioseismology, what have we really learned, and what do we aspire to learn?
• A method for the estimation of p-mode parameters from averaged solar oscillation power spectra

Cited by in corpus (29)

• Solar structure and evolution
• Time-distance helioseismology of solar Rossby waves
• Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
• Signatures of Solar Cycle 25 in Subsurface Zonal Flows
• Evidence for Large-Scale Subsurface Convection in the Sun
• Imaging the Sun's Far-Side Active Regions by Applying Multiple Measurement Schemes on Multi-Skip Acoustic Waves
• Changes in the solar rotation over two solar cycles
• Sensitivity of Helioseismic Measurements of Normal-mode Coupling to Flows and Sound-speed Perturbations
• Comparison of acoustic travel-time measurement of solar meridional circulation from SDO/HMI and SOHO/MDI
• Cycle dependency of a quasi-biennial variability in the solar interior
• Solar Cycle Variations of Rotation and Asphericity in the Near-Surface Shear Layer
• Detection of Rossby modes with even azimuthal orders using helioseismic normal-mode coupling
• Doppler velocity of $m=1$ high-latitude inertial mode over the last five sunspot cycles
• Changes in the sensitivity of solar p-mode frequency shifts to activity over three solar cycles
• Seismic Solar Models from Ledoux discriminant inversions
• Solar-cycle variation of the rotational shear near the solar surface
• Updated values of solar gravitational moments $J_{2n}$ using HMI helioseismic inference of internal rotation
• Helioseismic inference of the solar radiative opacity
• Inference of solar rotation from perturbations of acoustic mode eigenfunctions
• No swan song for Sun-as-a-star helioseismology: performances of the Solar-SONG prototype for individual mode characterisation
• Inferring solar differential rotation through normal-mode coupling using Bayesian statistics
• On the saturation of acoustic mode frequencies at high solar activity
• On the visibility of stellar oscillations
• Influence of the magnetic activity cycle on mean density and acoustic radius inversions
• Quantitative passive imaging by iterative holography: The example of helioseismic holography
• Sun's Seismic Radius as Measured from the Fundamental Modes of Oscillations and its Implications for the TSI Variations
• The ratio of horizontal to vertical displacement in solar oscillations estimated from combined SO/PHI and SDO/HMI observations
• Discovery of the First Octupole Pulsation Mode in a delta Scuti Star: A Stationary l = 3 Sectoral Mode
• Modeling HMI observables for the study of solar oscillations