Large-scale photospheric motions determined from granule tracking and helioseismology from SDO/HMI data

Abstract

Large scale flows in the Sun play an important role in the dynamo process linked to the solar cycle. The important large scale flows are the differential rotation and the meridional circulation with an amplitude of km/s and few m/s , respectively. These flows also have a cycle related components, namely the torsional oscillations. Our attempt is to determine large-scale plasma flows on the solar surface by deriving horizontal flow velocities using the techniques of solar granule tracking, dopplergrams, and time distance helioseismology. Coherent structure tracking (CST) and time distance helioseismology were used to investigate the solar differential rotation and meridional circulation at the solar surface on a 30 day HMI SDO sequence. The influence of a large sunspot on these large scale flows with a specific 7 day HMI SDO sequence has been also studied. The large scale flows measured by the CST on the solar surface and the same flow determined from the same data with the helioseismology in the first 1 Mm below the surface are in good agreement in amplitude and direction. The torsional waves are also located at the same latitudes with amplitude of the same order. We are able to measure the meridional circulation correctly using the CST method with only three days of data and after averaging between + and -15 degrees in longitude. We conclude that the combination of CST and Doppler velocities allows us to detect properly the differential solar rotation and also smaller amplitude flows such as the meridional circulation and torsional waves. The results of our methods are in good agreement with helioseismic measurements.

9 pages, 12 figures, accepted A&A 2017

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Cited by in corpus (8)

• Supergranular turbulence in a quiet Sun: Lagrangian coherent structures
• Long-Term Variations in Solar Differential Rotation and Sunspot Activity, II: Differential Rotation Around the Maxima and Minima of Solar Cycles 12-24
• Horizontal photospheric flows trigger a filament eruption
• Non-zero phase-shifts of acoustic waves in the lower solar atmosphere measured from realistic simulations and their role in local helioseismology
• Texture of average solar photospheric flows and the donut-like pattern
• Observational characterisation of large-scale transport and horizontal turbulent diffusivity in the quiet Sun
• Rotational radial shear in the low solar photosphere. Direct detection from high-resolution spectro-imaging
• Constraining Global Solar Models through Helioseismic Analysis