The US Air Force’s budding efforts to monitor the Sun’s activity helped avert potential nuclear conflict when a massive solar storm brought down radar and radio communications, Cold War historians have revealed.
On 23 May 1967, America prepared its aircraft for war in the belief that its surveillance radars in polar regions were being jammed by the Soviet Union. Just in time, military space weather forecasters were able to confirm that a solar storm was to blame. Planes remained on the ground and a situation that could have led to an exchange of nuclear weapons was avoided.
Nearly 50 years later, retired US Air Force officers who were involved in the incident have described it for the first time in a paper to be published in the American Geophysical Union journal Space Weather.
The US military began monitoring solar activity and space weather in the late 1950s. In the 1960s, a new branch of the Air Force's Air Weather Service monitored the sun routinely for the solar flares that can lead to electromagnetic disturbances on Earth which disrupt radio communications. AWS observers at locations in the US and abroad provided regular input to solar forecasters at the North American Aerospace Defense Command, a US and Canadian organisation responsible for controlling the region’s airspace.
On 18 May 1967 an unusually large group of sunspots with intense magnetic fields appeared in one region of the Sun. By 23 May observers and forecasters saw the sun was active and likely to produce a major flare. Observatories in New Mexico and Colorado saw a flare visible to the naked eye, while a solar radio observatory in Massachusetts reported the sun was emitting unprecedented levels of radio waves.
As the solar flare event unfolded, radars at all three of the Northern Hemisphere ballistic missile early warning system sites designed to detect incoming Soviet missiles appeared to be jammed. Any attack on these stations was considered an act of war. Aircraft laden with nuclear weapons were already on continuous alert, and commanders put additional forces in a ‘ready to launch’ status.
Retired Colonel Arnold L. Snyder, a solar forecaster at NORAD's Solar Forecast Center who was on duty that day remembers a tropospheric weather forecaster telling him the NORAD Command Post had asked about any solar activity that might be occurring.
"I specifically recall responding with excitement, 'Yes, half the sun has blown away,' and then related the event details in a calmer, more quantitative way," he recalls.
The study authors believe information from the Solar Forecasting Center made it to commanders in time to stop military action that could have included deployment of nuclear weapons. Public documents suggest information could have been relayed to the highest levels of government, and possibly even to President Lyndon B Johnson.
With the ‘jamming’ waning as solar radio emissions declined, it was realised that the Sun and not the Soviet Union that was to blame and the Air Force did not launch additional aircraft.
The geomagnetic storm went on to disrupt US radio communications for almost a week, however. It was so strong that the Northern Lights, usually only seen in or near the Arctic Circle, were visible as far south as New Mexico.
According to Delores Knipp, a space physicist at the University of Colorado in Boulder and lead author of the Space Weather paper, the storm's potential impact has been largely unknown until now and is a classic example of how geoscience and space research are essential to US national security.
"Had it not been for the fact that we had invested very early on in solar and geomagnetic storm observations and forecasting, the impact [of the storm] likely would have been much greater," she said. "This was a lesson learned in how important it is to be prepared."