McA: Background

In 1964 (Solar Cycle 20; SC 20), Patrick McIntosh began creating hand-drawn synoptic maps of solar magnetic features, tracing magnetic polarity inversion lines and connecting widely separated filaments, fibril patterns, and plage corridors to reveal the large-scale organization of the solar magnetic field. The maps were based on Hα daily images, and consistently from 1981 onwards, included coronal holes as a standard feature, primarily based upon ground-based He-I 10830 Angstrom images from NSO-Kitt Peak. However, coronal holes were first included for 3 rotations in 1978. Magnetograms were used to determine the overall dominant polarity of each region.

In all, 573 solar Carrington rotations (CROTs) were mapped between 1964 and 2009, beginning in CROT 1487 and continuing to CROT 2086, minus a gap between July 1974–June 1976 (CROT 1617-1642). There were originally 97 incomplete maps that are currently completed and 27 missing maps that are now recreated from original sources. In addition, all available coronal hole boundary data, beginning in 1974, have been included. The result is a record of ~45 years and 600 synoptic maps, —over four complete solar cycles, forming a uniquely consistent set of global solar magnetic field data [Link to PDF of original archive description].

For further background information see: https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-imagery/composites/synoptic-maps/mc-intosh/documentation/mca_background_2020.pdf