Probing the Solar Meridional Circulation Using Fourier Legendre Decomposition

Area of Science:

• Solar Physics
• Helioseismology
• Plasma Physics

Background:

• Understanding the Sun's internal dynamics, particularly meridional flow, is crucial for solar dynamo models.
• Previous helioseismic studies have provided insights into the Sun's internal structure and flows.

Purpose of the Study:

• To infer the depth variation of the Sun's mean meridional flow using helioseismic techniques.
• To investigate potential hemispheric differences in meridional circulation.
• To assess the consistency of observed flows with theoretical models.

Main Methods:

• Applied Fourier Legendre decomposition to 88 months of Helioseismic and Magnetic Imager (HMI) Dopplergrams.
• Developed control procedures to remove center-to-limb artifacts.
• Utilized forward modeling with sensitivity functions based on mode kinetic energy density.

Main Results:

• Inferred significant differences in meridional circulation between the northern and southern hemispheres.
• Detected a surprising equatorward propagating flow at ~40 Mm depth in the northern hemisphere.
• Results suggest potential systematic errors in HMI data, consistent with other findings.

Conclusions:

• The inferred northern hemisphere flow contradicts many existing helioseismic analyses.
• Methodological limitations in artifact removal may explain discrepancies.
• Further investigation is needed to reconcile HMI data with other solar observations.