1. Helioseismic Holography & some experiments on “field effects” in CR1988 NorthWest Research Associates Colorado Research Associates Division D. Braun

2. daily flow map 1 “day” = 27.3 hr –Sun rotates 15° Postel projections –3 x 3 mosaic covering 120° x 120° –each tile: 40°x40° (cropped from 60°x60° box) flow-sensitive holography in 3D Fourier domain in each box

3. depth sensitivity what I’m showing here: –is not an inversion –is derived from E-W and N-S holographic phase signatures calibrated from different tracking rates represent a kind of average from surface down to ~focus depth inversions will be discussed in H8

4. typical daily map (flows averaged over 15° boxes)

5. “field effects” systematic (and spurious) flows associated with fixed spatial position on the disk may result from –foreshortening –image distortions –projection deficiencies –Carrington element errors –spatially varying frequencies across the disk –etc.

6. assessing field effects make “field-effect map” from all days – average of all daily maps without rotational shifting in longitude –a longitudinal mean is subtracted (i.e. it is assumed this is real; e.g. meridional, ARs, but…??) –spatially smeared (Gaussian FWHM = 7.5°) assess Postel distortion for single day –compare 3x3 (40° spaced) and 15x15 Postel (8° spaced) tiling –difference is a proxy of likely Postel distortions –lazy way of avoiding spherical geometry coding

7. field-effect maps

8. B and L components:

9. variations with depth and instrument (B component only) MDI GONG depth = 3Mm7 Mm14 Mm30 Mm note: corner & edge features more pronounced in northern hemisphere

10. 3x3 and 15x15 tiling comparison (B component only) depth = 3 Mm

11. comparing Postel distortion & field effect maps

12. after Postel distortions are subtracted, what’s left in the field effect map?

13. a possible explanation:

14. can we believe things like this?