1 / 20

holographic measurements of simulated flows

holographic measurements of simulated flows. Doug Braun and Aaron Birch. using 48x48x20 Mm simulations provided by R. Stein, Å . Nordlund, D. Bensen, D. Georgobiani. NorthWest Research Associates, Inc. Colorado Research Associates Division. conclusions.

deborahfay
Download Presentation

holographic measurements of simulated flows

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. holographic measurements of simulated flows Doug Braun andAaron Birch using 48x48x20 Mm simulations provided by R. Stein, Å. Nordlund, D. Bensen, D. Georgobiani NorthWest Research Associates, Inc. Colorado Research Associates Division

  2. conclusions • near-surface helioseismic holography (hh) signatures are clearly correlated with mean horizontal flows – hh “works” • hh signatures focused below surface have ~equal contributions from surface (<2Mm) and below; both decrease rapidly with depth: • surface contribution decreases due to cancellation of signals from neighboring convective cells (previously suspected and modeled in solar SG) – can cause “reversal”-like signature • subsurface contributions decrease with ratio of flow/sound-speed • assessment of noise with forward models: • flows like these can only be detected (at resolutions of ~6Mm) down to depths ~5-7 Mm • deeper assessment of solar flows (like these) may require combining many supergranules • these types of simulations are critical to helioseismology LoHCo Meeting, Boulder

  3. convective flows “visible” to p modes (8 hr duration) LoHCo Meeting, Boulder

  4. depth variations of mean (8-hr) flows x x y y LoHCo Meeting, Boulder

  5. “reversal” at depth > 12 Mm slope: velocities over near-surface values LoHCo Meeting, Boulder

  6. helioseismic holography (hh) of flows “lateral vantage” N E W S H- = ingression H+= egression LoHCo Meeting, Boulder

  7. hh of flows (continued) N E W S in temporal Fourier domain, correlations between egression and ingression are simply a product, e.g. the E-W correlation is: the argument of the correlation averaged over a frequency bandpass is a phase shift: the phase difference between E-W and W-E is sensitive to a flow in x direction : this phase difference is equivalent to a travel-time perturbation: LoHCo Meeting, Boulder

  8. power spectra LoHCo Meeting, Boulder

  9. EW hh travel-time maps at different frequencies focus depth = 0.7 Mm 3 mHz 4 mHz mean 5 mHz 6 mHz mean velocity Vx (0.7 Mm) LoHCo Meeting, Boulder

  10. hh “calibrated” flows • calibration constant determined by introducing a known tracking rate • different calibration for each frequency bandpass • average 3,4,5, and 6 mHz bandpasses • resulting “velocities” represent weighted average over depth LoHCo Meeting, Boulder

  11. 8-hr mean flows at 0.7 Mm (smoothed to FWHM = 6 Mm) hh calibrated flows, focus = 0.7 Mm Vx Ūx X Ūy Vy y LoHCo Meeting, Boulder

  12. hh travel-time maps vs. focus depth travel-times, focus = 0.7 Mm focus = 0.7 – 7 Mm EW NS LoHCo Meeting, Boulder

  13. decrease of hh travel-time signatures • ratio of signatures to surface values fall-off faster than actual flow speed ratios • effects of lower boundary impede measurements at and below 8 Mm • possible reversal in NS signature below 6 Mm slope: travel times over near-surface values LoHCo Meeting, Boulder

  14. reversal of supergranular hh signatures div vh pupil v ~ e-z/zo cos(z/z1) zo =2.5 Mm. red crosses : no return flow (z1). green circles: z1= 5 Mm black diamonds: z1= 15 Mm. (Braun, Birch, & Lindsey 2004 SOHO/GONG Proceedings) LoHCo Meeting, Boulder

  15. observed vs. forward-modeled hh travel times depth = 3Mm model obs obs-model 3 mHz r.m.s. = 10 s 3-6 mHz r.m.s = 5 s LoHCo Meeting, Boulder

  16. assessment of relative depth contributions depth = 3 Mm < 2 Mm > 2 Mm total LoHCo Meeting, Boulder

  17. depth = 5 Mm < 2 Mm > 2 Mm total LoHCo Meeting, Boulder

  18. depth = 7 Mm < 2 Mm > 2 Mm total LoHCo Meeting, Boulder

  19. signal-to-noise • assumes these flows are typical of Sun • assumes smearing of ~6Mm; can sacrifice spatial resolution to increase S/N • assumes only 3-5 mHz for Sun (not 3-6 mHz) • assumes good assessment of shallower contributions LoHCo Meeting, Boulder

  20. conclusions • near-surface helioseismic holography (hh) signatures are clearly correlated with mean horizontal flows – hh “works” • hh signatures focused below surface have ~equal contributions from surface (<2Mm) and below; both decrease rapidly with depth: • surface contribution decreases due to cancellation of signals from neighboring convective cells (previously suspected and modeled in solar SG) – can cause “reversal”-like signature • subsurface contributions decrease with ratio of flow/sound-speed • assessment of noise with forward models: • flows like these can only be detected (at resolutions of ~6Mm) down to depths ~5-7 Mm • deeper assessment of solar flows (like these) may require combining many supergranules • these types of simulations are critical to helioseismology LoHCo Meeting, Boulder

More Related