IMF Sector Boundaries 1926-2010 (updated)

Description from Leif Svalgaard:

The last two numbers are the number of days of each polarity on each side of the boundary, so " +,- 2010 01 06 16 4 " means that there are 16 '+' days before the boundary and 4 '-' days after. This is to make it easy to do analysis, e.g. isolated SBs.

The method of deciding is basically the same as in the earlier Svalgaard atlases: Atlas of IMF Polarity 1947-1975.pdf (SUIPRs 629 and 648) also found on my website. Basically I make the 'best' guess, IMF having double weight of ground-based. This makes the list non-homogeneous, but so be it. Four days of duration is my general criterion for a sector, but I'm not religious about it, and occasionally, thinner sectors are included if they are clear and recurrent. Using the numbers on the right you can make your own selection.

In the past, I did the assignment 'by eye', now I have a simple computer algorithm to do it. It involves as slight smoothing to essentially disregard mixed or too tiny sectors. No visual quality control has been performed [I trust my algorithm more than my personal bias].

Svalgaard SB 1926-present

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