Helioseismic%20Holography%20

1
Helioseismic Holography some experiments on
field effects in CR1988
D. Braun

• NorthWest Research Associates
• Colorado Research Associates Division

2
daily flow map

• 1 day 27.3 hr
• Sun rotates 15
• Postel projections
• 3 x 3 mosaic covering 120 x 120
• each tile 40x40 (cropped from 60x60 box)
• flow-sensitive holography in 3D Fourier domain in
  each box

3
depth sensitivity

• what Im 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
depth 3Mm
7 Mm
14 Mm
30 Mm
GONG
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, whats
left in the field effect map?
13
a possible explanation
14
can we believe things like this?