Space storms that go off-scale

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Friday, February 8, 2019

Terrestrial and space weather storm scales have a common shortcoming: The scales end at “5.” Nature of course doesn’t know this and sometimes produces a disturbance that is simply off the charts. Based on the damage done to telegraph systems and sightings of the aurora at low latitudes, the great space weather storm of September 1859 was largely off-scale. Named after the astronomers who wrote about it, the Carrington-Hodgson storm (aka, Carrington Storm) has been a defacto standard for extreme space weather beyond category “5”. Scientists have long theorized about how often such extreme storms occur. Surely, they would know if such a storm had occurred during the space age; and certainly, NOAA would have the records. Professor Delores Knipp, Senior Research Associate at the High Altitude Observatory reports that indeed a Carrington-class storm did occur in August of 1972…and yes NOAA has many of the records, as do many other data depositories and archival publications. But the storm didn’t behave exactly like the Carrington-Hodgson storm.

Image of Hydrogen-α solar spectroheliogram
Hydrogen-α solar spectroheliogram of flaring region at 0648 UT on 4 August 1972. Copyright BASS2000, Paris Observatory, PSL (used with permission).

Knipp looked at space storm effects on other technologies; power grids, radio signals, spacecraft solar panels, and amazingly, low-latitude sea mines. When all of the records come together they tell an amazing story of the fastest recorded solar mass ejection with a Sun-to-Earth transit time 14.6 hours. This was paired with a long duration (>16 hr) solar flare that saturated spacecraft detectors. In an extraordinary turn of events the flare was still in progress when the ejecta reached Earth. The space radiation storm was extreme. As far the low latitude sea mines were concerned, the sudden impulse in Earth’s magnetic field apparently contributed to magnetic signals at low latitudes that mimicked the signal of passing ships. The US Navy, then in the throes of the Vietnam War, had to replace roughly 4000 mines that were part of the harbor-blocking strategy to end the war.

In her American Meteorological Society “Fellow” presentation (9 January 2019) and in her published paper, Knipp urges the Space Weather community to assess whether upstream monitoring systems, vulnerable technologies and humans in space are prepared for a repeat event.

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