SOHO CoRoT Kepler Picard SDO GONG

The Meridional flow as derived from Fourier-Legendre decomposition of the first data from the Helioseismic and Magnetic Imager


Doerr Hans-Peter


Kiepenheuer-Institut für Sonnenphysik


First results from new space missions
Auteur(s) supplémentaire(s)Roth, Markus


The Fourier-Legendre decomposition (FLD; Braun 1998) technique is a convenient method for measurements of the solar meridional flow. The surface oscillation signal on each hemisphere is decomposed into mode coefficients of travelling wave fields propagating in poleward and equatorward direction. Due to the meridional flow, both wave fields experience a doppler shift. From the measured frequency shift and the solar "Model S" by Dalsgaard et. al (1996), we derive the velocity of the meridional flow by means of a SOLA (Substractive Optimized Local Averaging; Pijpers & Thompson 1992) inversion method. Since FLD is sensitive to low-degree modes it has the potential to probe the meridional flow down to much deeper layers as it is currently possible with other methods such as ring diagram analysis (Hill 1988).

We implemented the FLD method in a code pipeline (Doerr et. al 2010; submitted) that can be used to process data from the ground-based Global Oscillation Network Group (GONG) as well as the space-born Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) instruments. First flow velocities derived from FLD are qualitatively in good agreement to those obtained from ring diagram analysis of the same time series.

We present flow maps as derived from Fourier-Legendre decomposition of the first data available from the HMI instrument
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