2019 AMS Fellow Talk: The Last Gasp of Solar Cycle 20 and the Little-Known Consequences of the August 1972 Ultra-Fast Coronal Mass Ejecta (Invited Presentation)

In early August 1972, near the end of solar cycle 20, the Sun produced a series of flares and coronal mass ejections (CMEs) that bear the signatures of a Carrington-level event. The ejecta associated with the 4 August X-class flare arrived at Earth in only 14.6 hr. This transit was made possible by the path-clearing efforts of two previous CMEs that arrived early on 4 August. Charged particles caught between complex interplanetary structures were energized into a swarm of solar energetic particles producing a greater than 10 MeV ion flux of 70000 cm^-2 s^-1 sr^-1. These particles punished spacecraft solar panels and produced an ozone hole in the stratosphere that persisted and circulated as a semi-rigid structure for more than 50 days. Within 15 minutes of the late 4 August shock arrival the first glow of what would become a “spectacular aurora,” bright enough to cast shadows, appeared along the southern coast of the United Kingdom at ~54 MLAT. Widespread electric- and communication- grid disturbances plagued North America late on 4 August as high-latitude magnetic field rates of changes exceeded 2000 nT/min. Giant magnetic pulsations rocked the magnetosphere. Over Russia there was reported development of a nighttime mid-latitude E-layer. Although, the magnetic storm index, Dst, dipped to only -125 nT, the magnetopause was observed within 5.2 R_E and the plasmapause within 2 R_E. There was an additional effect, long buried in the Vietnam War archives that adds credence to the severity of the storm impact: a nearly instantaneous, unintended detonation of dozens of sea mines south of Hai Phong, North Vietnam on 4 August 1972. The US Navy attributed the dramatic event to ‘magnetic perturbations of solar storms.’ We provide insight into the solar, geophysical and military circumstances of this extraordinary situation. We further argue that this storm deserves a scientific revisit as a grand challenge for the space weather community.