1. Rachel Howe, NSO December 2005
The trouble with 2004
Rachel Howe, NSO
December 2005

2. Introduction
Howe et al have recently submitted a paper on near-surface zonal flows, using MDI global and ring data and MtW Doppler
MDI had a dynamics run in 2004, and the data went through the Stanford/Colorado ring pipeline
However, the data were not included in our paper.
Why not?
Can the data be fixed?

3. Synopsis The data Analysis
Year-to-year variations in MDI zonal flows from ring diagrams.
Qualitative differences in the 2004 data.
Possible explanations (and rebuttals)

4. The Data MDI dense-pack ring diagram analysis 1996-2004 dynamics runs
Flows averaged over CR (RLS) or year (OLA)

5. The problem

6. Zonal flows over time
Color-coded by latitude

7. Comments Gentle downhill trend with time
Zonal flows go negative in 2004!
Also, the variation with latitude changes.

8. Zonal flow depth profiles
‘Corrected’ to same value at surface
Color-coded by year
2004 is red.

9. Comments
The 2004 zonal flows show qualitatively different behavior as a function of depth.
2003 shows some signs of problems too.
Effect is most pronounced at high latitudes.

10. What could have caused this?
The Sun?
No, GONG doesn’t show it.
Serious tracking errors?
Seems unlikely – cubes look normal.
Changeover to Linux?
No, that happened partway through and only makes a jump in mode amplitudes.

11. Any ideas?
Has anyone seen anything similar in other analyses of the 2004 data?
Could there have been instrument or orbit changes?
Is there any way to fix the data?