Helioseismic Holography& some experiments on “field effects” in CR1988

NorthWest Research Associates

Colorado Research Associates Division

D. Braun

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

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

typical daily map (flows averaged over 15° boxes)

“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.

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

field-effect maps

B and L components:

variations with depth and instrument (B component only)

MD

IG

ON

G

depth = 3Mm 7 Mm 14 Mm 30 Mm

note: corner & edge features more pronounced in northern hemisphere

3x3 and 15x15 tiling comparison(B component only)

depth = 3 Mm

comparing Postel distortion & field effect maps

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

a possible explanation:

can we believe things like this?