August 4, 1972: The Day the Sun, the Earth and an Ultra-fast Coronal Mass Ejection Aligned to Produce Historic Space Weather

Abstract:

The space weather community has few analogs for a Carrington-class storm. We have witnessed the July 23 2012 event from the sidelines. Unknown to most, Earth was likely hit by a Carrington-class storm on 4 August 1972 (Knipp et al. 2018)*. The observations that point to such a conclusion will be organized and described in this presentation. These include: 1) a flare that saturated spacecraft X-ray detectors at X5.5 (see accompanying image of H-alpha flare)**; 2) an associated ultra-fast shock/coronal mass ejection (CME) that arrived at Earth in 14.6 h; 3) a swarm of solar energetic particles; and 4) a series of sudden impulses in Earth’s magnetic field. The latter of these rocked the dusk-sector, North American power grid and apparently triggered dozens (and probably thousands) of sea-mine detonations at local dawn in the coastal waters off Vietnam. I will further discuss: 1) The alignment of shock and CME circumstances that made this such a violent storm, yet somehow, a storm that has been overlooked and 2) The implications for forecasting extreme space weather.

* Knipp, Delores, Brian J. Fraser, M. A. Shea, D. F. Smart, On the Little-Known Consequences of the 4 August 1972 Ultra-Fast Coronal Mass Ejecta: Facts, Commentary and Call to Action, Space Weather, DOI:10.1029/2018SW002024

**Copyright BASS2000, Paris Observatory, PSL. (Used with Permission)