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Persistent structures in near-surface flows from ring diagrams

Persistent structures in near-surface flows from ring diagrams. Rachel Howe, University of Birmingham D. Baker, L. Harra , MSSL R. KomM , NSO R. Bogart, Stanford. Probing the sun inside and out. Leverhulme -funded project at MSSL 1 st Workshop June 2011. Introduction.

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Persistent structures in near-surface flows from ring diagrams

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  1. Persistent structures in near-surface flows from ring diagrams Rachel Howe, University of Birmingham D. Baker, L. Harra, MSSL R. KomM, NSO R. Bogart, Stanford

  2. Probing the sun inside and out Leverhulme-funded project at MSSL 1st Workshop June 2011

  3. Introduction • The Sun has flows at many scales, from global rotation to flows around active regions and down to granules. • Many of these show variations with solar cycle. • Here we are looking for persistent structures in local flow features over an extended period.

  4. Differential rotation • 2D rotation profile, based on RLS inversions • Faster near equator, slower at poles

  5. Analysis • Use synoptic maps of zonal/meridional flows from ring diagrams (GONG and HMI) • Average over all depths • At each latitude and rotation, we subtract mean over all times/longitudes to remove differential rotation and first-order temporal variations such as the torsional oscillation (as well as systematic effects) • Then plot residuals as longitude—time maps • Differential rotation causes features to drift in longitude from one rotation to the next. • Features (e.g., flows into active regions/remnants) persisting for more than one rotation will show up as diagonal streaks

  6. GONG zonal velocitylongitude—time plots Note diagonal ‘grain’ Paired light-dark streaks suggest flows into or out of feature that drifts with differential rotation. Slope up == faster than Carrington rate Slope down == slower than C.R. Shallower slope means more difference.

  7. GONG Meridional velocity Not much to see here – quieter at minimum?

  8. MDI/HMI Magnetograms (Timescale of GONG) Note slope of features differs from that seen in flows

  9. GONG zonal velocity On HMI timescale.

  10. HMI zonal velocity Note strong stripes at high latitudes. For common data, correlation with GONG is > 80%

  11. HMI meridional velocity Some grain visible here too.

  12. HMI Magnetograms

  13. Differential rotation Use cross-correlation analysis to translate stripes slope to rotation rate Green – Magnetograms Black – Global inversions Red – HMI ring vx correlation Blue – GONG ring vx correlation

  14. Differential rotation Use cross-correlation analysis to translate stripes slope to rotation rate Green – Magnetograms Black – Global inversions Red – HMI ring vx correlation Blue – GONG ring vx correlation Cyan – EIT 195 Angstrom correlation Orange – GONG PFSS coronal hole maps

  15. High-latitude vx rewrapped with estimated velocity

  16. High-latitude vx rewrapped with est. velocity -5 nHZ

  17. Discussion • Near-surface flows –especially zonal – show signatures of features persisting from a few to many rotations, migrating as would be expected from differential rotation. • Low latitudes traceable to active region/plage? • Rotation rate from magnetic features not quite the same as from flows – anchoring depth? • High latitudes – Hathaway giant cells? Looks like an l=1 structure, anticorrelated n/s. • Correlation analysis not good enough to pick up changes in differential rotation.

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