C H A P T E R

N ° 17

The 1972 Black Swan Event

Image Credit: NASA: Shows material erupting from a flare near the limb of the Sun on the 10’th of October 2971.

Image Credit: NASA: Shows a powerful flare observed on the disk of the Sun on the 7’th of October 1972. The flare is an example of a ‘two-ribbon’ flare in which the flaring region appear as two bright lines threading through the area between sunspots within a sunspot group. The particular flare shown is called the ‘seahorse flare’ and produced radiation levels that would have been harmful to astronauts if a moon mission had been in progress at the time

Between the 2nd and the 4th of August 1972, a coronal hole named Region 11976 located around the Sun’s equator produced a series of flares, energetic particle enhancements, and Earth-directed plasma clouds. Two of the four flares that erupted from the Sun generated two impulses in the Earth’s magnetic field. Shortly after, on the 4th of August, these two flares were followed by a geomagnetic storm. The storm was caused by a Coronal Mass Ejection (CME) that had been estimated to have a record arrival time of only 14.6 hours with an average transit speed of 2.850 km/s. This transit time was argued by scientists like A. J. Freed and C.T. Russell to be unusual even for the family of the extreme events they studied at the time in 2014. Today it is found to be the fastest ever recorded, as Coronal Mass Ejections usually generally take around three days to reach Earth.

On the current American National Oceanic and Atmospheric Administration (NOAA) space weather classification scale, the solar flares were estimated to be X-class flares with a 5.1 magnitude. However, through the use of ionospheric radio wave phase propagation disturbances, estimations conducted by scientist M. Ohshio in 1974 showed that the solar flares were, in fact, X-class solar flares with a magnitude of approximately 20.

The X-ray emissions from the flares remained above background for approximately 16 hours. On the Comprehensive Flare Index developed by Helen W. Dodson and E. Ruth Hedeman it was categories as 17, which makes it categorised as one of the most extreme and broad-spectrum flares detected. According to physicist E.H. Levy, the event produced one of the largest Galactic Cosmic Ray (GCR) eruptions/dropout of the space age.

Image Credit: Paris Observatory: Showing McMath Region 11976 August 1972. Image a); shows the sunspot and surrounding plasma in ultraviolet light on 3’rd of August 1972. Image b); shows a flare in progress in visible light on the 4’th of August 1972.

How was it experienced on Earth?

The series of solar storms in 1972 brought to light several significant threats posed by space weather events.

At 29.54 and 22.38 UT on the 4th of August 1972 magnetometer traces went off scale in the U.S. and at low-altitude India. Following this was bright aurora in the Northern U.S. Within 15 minutes the first glow of what would become a spectacular aurora that was bright enough to cast shadows appeared along the southern coast of the United Kingdom at ~54° MLAT (multilateration). Within 2 hours commercial airline pilots reported visible aurora as far south as Bilboa, Spain, at ~46° MLAT. Auroral disturbances continued into the 5th of August with reports of intense midday red aurora in the dark Southern Hemisphere.

Furthermore, as the Coronal Mass Ejection (CME) hit the Earth’s magnetosphere, it created Geomagnetically Induced Currents (GICs), consequently causing major fluctuations in power grids in North America and Canada, and communications lines. Numerous United States and Canadian power companies reported minor to strong power issues on the 4’th and 5’th of August 1972.  The Geomagnetically Induced Current (GIC) disturbances were seen as far as the states Maryland and Ohio in the U.S.

In Newfoundland, Canada, Geomagnetically Induced Currents (GICs) activated protective relays numerous times on the 4th and 5th of August, as the induced currents exceeded shutdown threshold for high currents. The Canadian Manitoba Hydro Company recorded 120 MW (medium wave) drops in power supplied to Minnesota in only a few minutes. C. W Anderson et al. (1974) reported an outage on the L4 American Telephone and Telegraph cable connecting the U.S. states of Illinois and Iowa.

The space weather event did not only effect terrestrial infrastructures. In the near-Earth space environment, spacecrafts were equally struggling. The chain of events from the space weather event led to extraordinary effects, including a solar energetic particle (SEP) event that punished solar panels onboard spacecrafts, and satellite detectors. Within minutes of the space weather event occurring, dayside radio blackouts occurred.

The proton flux on the Interplanetary Monitoring Platforms spacecraft dramatically increased around 20.54 UT during the 4th of August. The maximum particle flux was so intense that the particle detectors were saturated. This resulted in uncertainty as to the actual magnitude of the particle increase. Moreover, the flux peak also triggered the event mode data compression algorithm on the Vela satellites’ neutron counter that was monitored in real time at Air Force Global Weather Central (AFGWC) for nuclear test ban verification. These energetic proton fluxes produced a ground level event.

A report by Brace et al. (1974) indicates that the energetic electrons invaded the radiation belt slot region, while Spjeldvik and Fritz (1981) reported an increase in the orders of magnitude in the trapped energetic heavy ion population (Z ≥ 4) within the radiation belts and slot region (L ~ 2.5–5) between the 4’th and 5’th of August.

The most unexpected and choking effect of the 1972 storm appeared on August the 4th in North Vietnam. On the 4’th of August, 1972, U.S. military pilots flying south of Haiphong harbor in North Vietnam saw something unexpected. More than two dozen of U.S. naval sea mines suddenly exploded in the water without apparent explanation. The sea mines were designed to register the magnetic fields created by passing ships. Following this event, investigations were made by the U.S. with personnel from the National Academy of Science, the National Oceanic Atmospheric Administration (NOAA), various U.S. Naval laboratories, and the Naval Post Graduate School. They concluded that the sensitive sensors on the mines must have been triggered by the magnetic perturbations of the solar storms. A reason for the conclusion was that aerial inspections revealed that similar detonations had been occurring elsewhere along the coast. In total, the space weather event caused the premature detonation of over 4000 U.S. magnetically sensitive destructor mines (DSTs). This caused immediate and long-term actions, such as the replacement of the sensitive sensors ‘magnetic-influence-only mines’ with ‘magneto/seismic mines’.

Image Credit: United States Navy: Shows U.S. ships en route to begin ‘Operation End Sweep’ in 1973, a campaign to remove thousands of sea mines placed around North Vietnam during the Vietnam War.

Image Credit: United States Navy: Shows a sea mine exploding off the coast of North Vietnam during ‘Operation End Sweep’.

The 1972 Space Weather Event and today’s modern society

The August 1972 space weather event highlights the world’s current vulnerability to similar space weather events. The incident with the exploding mines, the issues with satellites, power grids etc. gives the world a sense of range of what space weather can do and what the impacts could look like. This is especially if we do not invest in research and increase awareness in all critical infrastructures, and create and implement mitigation measures where needed.

Today the extreme space weather events of early August 1972 are discussed as benchmarks for Sun-Earth transit times of solar ejecta (14.6 hours) and for solar energetic particle fluxes (10 MeV ion flux >70,000 cm−2·s−1·sr−1). Furthermore, it is compared to the famously referred to space weather event by the name Carrington Event from 1859. Although we today may see the 1972 event as an indication of what could happen during a Carrington-class event, many solar observers at the time thought the event to be a typically occurring event.

*To learn more about the 1859 Carrington Event, read SR Hoplon’s blog 2024 C H A P T E R N ° 2’1 Historical Space Weather Events.*

Estimation or observation errors such as these reinforces the argument of the need of multiple types of mitigation measures in the form of engineering and non-engineering-based mitigation measures. Communities such as the Disaster Risk Reduction (DRR) community must be aware and prepared for such unpredictable events in order to, for example, be ready to act during the time of emergencies. 

As we continue to explore and expand our presence in space and the development of technology, understanding and planning for space weather events is becoming increasingly important. Being aware, prepared, and resilient to space weather impact is a must for the security of the modern-day and future society.

Source

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