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?