Sector boundaries are the times observed at Earth when the polarity of the interplanetary magnetic field (IMF) reverses. Well defined sector boundaries are those boundaries for which there is good data, the reversal takes place cleanly, and intervals on either side of the boundary have a uniform field direction for ~4 days.
Over the years a number of sector boundary lists have been compiled. They depend on interplanetary magnetic field polarities inferred from geomagnetic observations and observed by spacecraft.
Each of the following 4 lists is different and you are strongly encouraged to read the accompanying notes to understand the differences.
The data used to determine these boundaries come from a wide variety of sources and we are sincerely grateful to those whose dedicated efforts and willingness to share their observations have aided this work.
Sector Boundaries 1947-1982
Sector Boundaries 1982-1988
Sector Boundaries 1988-1993
L. Svalgaard's list 1926-present
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