Science Seminars

The Great Space Weather Storm of 4-5 August 1972 – A Carrington-class Storm in Disguise?

Speaker: Delores Knipp (CCAR, CU Boulder; NCAR/HAO)
Date: Thursday, Feb 28, 2019
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

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-20 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 RE and the plasmapause within 2 RE. 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’.  I provide insight into the solar, geophysical and military circumstances of this extraordinary situation.  I further argue that this storm deserves a scientific revisit as a grand challenge for the space weather community.