Spatially resolved vertical vorticity in solar supergranulation using helioseismology and local correlation tracking
arXiv:1504.00223 · doi:10.1051/0004-6361/201526024
Abstract
Flow vorticity is a fundamental property of turbulent convection in rotating systems. Solar supergranules exhibit a preferred sense of rotation, which depends on the hemisphere. This is due to the Coriolis force acting on the diverging horizontal flows. We aim to spatially resolve the vertical flow vorticity of the average supergranule at different latitudes, both for outflow and inflow regions. To measure the vertical vorticity, we use two independent techniques: time-distance helioseismology (TD) and local correlation tracking of granules in intensity images (LCT) using data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Both maps are corrected for center-to-limb systematic errors. We find that 8-h TD and LCT maps of vertical vorticity are highly correlated at large spatial scales. Associated with the average supergranule outflow, we find tangential (vortical) flows that reach about 10 m/s in the clockwise direction at 40° latitude. In average inflow regions, the tangential flow reaches the same magnitude, but in the anti-clockwise direction. These tangential velocities are much smaller than the radial (diverging) flow component (300 m/s for the average outflow and 200 m/s for the average inflow). The results for TD and LCT as measured from HMI are in excellent agreement for latitudes between 60° and 60°. From HMI LCT, we measure the vorticity peak of the average supergranule to have a full width at half maximum of about 13 Mm for outflows and 8 Mm for inflows. This is larger than the spatial resolution of the LCT measurements (about 3 Mm). On the other hand, the vorticity peak in outflows is about half the value measured at inflows (e.g. 4/(10^6 s) clockwise compared to 8/(10^6 s) anti-clockwise at 40° latitude). Results from MDI/SOHO obtained in 2010 are biased compared to the HMI/SDO results for the same period.
12 pages, 13 figures (plus appendix), accepted for publication in A&A
References in corpus (5)
- Evidence of photospheric vortex flows at supergranular junctions observed by FG/SOT (Hinode)
- Linear Sensitivity of Helioseismic Travel Times to Local Flows
- Time-distance helioseismology: Sensitivity of f-mode travel times to flows
- The existence of the Lambda effect in the solar convection zone indicated by SDO observations
- Time-distance helioseismology: A new averaging scheme for measuring flow vorticity
Cited by in corpus (29)
- Global-scale equatorial Rossby waves as an essential component of solar internal dynamics
- Seismic Sounding of Convection in the Sun
- DeepVel: deep learning for the estimation of horizontal velocities at the solar surface
- Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
- Tilt Angle and Footpoint Separation of Small and Large Bipolar Sunspot Regions Observed with HMI
- Supergranulation and multiscale flows in the solar photosphere: Global observations vs. a theory of anisotropic turbulent convection
- Power-Law Statistics Of Driven Reconnection In The Magnetically Closed Corona
- Average motion of emerging solar active region polarities I: Two phases of emergence
- The shrinking Sun: a systematic error in local correlation tracking of solar granulation
- Evolution and wave-like properties of the average solar supergranule
- Anisotropy of the solar network magnetic field around the average supergranule
- Improved Measurements of the Sun's Meridional Flow and Torsional Oscillation from Correlation tracking on MDI \& HMI magnetograms
- Data compression for local correlation tracking of solar granulation
- Interaction of solar inertial modes with turbulent convection. A 2D model for the excitation of linearly stable modes
- Formation of Quiescent Prominence Magnetic Field by Supergranulations
- Intensity contrast of the average supergranule
- The Dynamic Coupling of Streamers and Pseudostreamers to the Heliosphere
- Analyzing supergranular power spectra using helioseismic normal-mode coupling
- Imaging the Sun's near-surface flows using mode-coupling analysis
- Coriolis force acting on near-surface horizontal flows during simulations of flux emergence produces a tilt angle consistent with Joy's law on the Sun
- Plasma flows and sound-speed perturbations in the average supergranule
- The amplitude of the cross-covariance function of solar oscillations as a diagnostic tool for wave attenuation and geometrical spreading
- Comparison of Travel-Time and Amplitude Measurements for Deep-Focusing Time--Distance Helioseismology
- Relationships between fluid vorticity, kinetic helicity and magnetic field at the small-scale (quiet-network) on the Sun
- Characterizing the spatial pattern of solar supergranulation using the bispectrum
- 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
- Helioseismological determination of the subsurface spatial spectrum of solar convection: Demonstration using numerical simulations
- Investigating toroidal flows in the Sun using normal-mode coupling