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Sector Structure of the Interplanetary Magnetic Field

The interplanetary magnetic field (IMF) is formed by the solar wind (solar plasma flow), which carries away the coronal magnetic field into the interplanetary medium. Frozen in the plasma, this magnetic field lines form an interplanetary magnetic field.

The IMF polarity is the direction along the field lines to the Sun (negative polarity) or from it (positive). It is determined mainly by the magnetic fields of sunspots directed in different ways (both towards the Sun and from it).

The main characteristic of the IMF is the sector structure — the division of the observed large-scale structure of the solar wind into an even number of sectors with different directions of the radial component. In the plane of the Ecliptic, a sector structure of the IMF is formed. Most often, 2 or 4 sectors are observed with alternating IMF of opposite polarity. The sector boundaries are located in the area of the slow solar wind flow, and the sector center is located in the area of the fast solar wind flow.

The combination of the expansion of the solar wind with rotation of the Sun leads to the fact that the magnetic lines of force frozen into the solar wind have a shape close to the spirals of Archimedes.

Studying the variations of the geomagnetic field at polar stations, L. Svalgaard and S. Mansurov independently discovered that depending on the polarity of the sector, different types of the geomagnetic field variations are observed at high-latitude magnetic stations (Tule and Vostok).
By investigating the corresponding variations of the geomagnetic field components, it is possible to restore the polarity of the IMF and reconstruct the sector structure of the IMF.

Adopted polarity of IMF for each day , 1947-1975

Source Link: Svalgaard L. Interplanetary Sector Structure 1947-1975. Institute for Plasma Research. Stanford University. SUIPR Report No. 648, February 1976.

Table of the most probable times of sector boundary crossings (1947-1978),
when the polarity of the IMF is reversed, compiled by L. Svalgaard.

Continuation on the web page of L. Svalgaard

Table of the number of days of each polarity on each side of the sector boundary from 1926 to the present

Source Link: Svalgaard L. Interplanetary magnetic‐sector structure, 1926–1971. Journal Geophysical Research, Space Physics. 1972. V. 77. Is. 22.

Sector Structure of the Interplanetary Magnetic Field.
IMF polarity distribution over 27-day periods (according to Bartels)
on the website of the N.V.Pushkov Institute of Earth's magnetism, ionosphere and radio wave propagation, Russian Academy of Sciences IZMIRAN.

Table and plot of IMF azimuthal angles (1965-present),
computed from daily averages of hourly GSE X and Y IMF components.

Source Link: OMNIWeb data service at Space Physics Data Facility, Goddard Space Flight Center.

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