9:50 AM | *It was during the height of the Cold War and a solar storm nearly sparked a nuclear war*

A solar image on May 23rd, 1967 features a bright region (top, center) which is where the solar flare occurred on that day. Credit: National Solar Observatory historical archive, American Geophysical Union

Overview
It was during the height of the Cold War and a powerful solar storm could have led to a disastrous military conflict between the US and Soviet Union if not for the early efforts of the US Air Force to monitor solar activity. On May 23rd, 1967, a solar storm took place that was so powerful, it jammed radar and radio communications in polar regions and the US Air Force actually began to prepare aircraft for war thinking the nation’s surveillance radars were being jammed by the Soviet Union.  Fortunately, space weather forecasters in the military suspected there might be another cause and they relayed information about the possibility that a solar storm could have been the reason for the disrupted radar and radio communications.  As it turned out, this information was enough to keep the planes on the ground and the US avoided a potential nuclear weapon exchange with the Soviet Union.

Early efforts on monitoring the sun
The US military began monitoring solar activity and space weather disturbances in the upper atmosphere during the latter part of the 1950’s.  By the 1960’s, the US Air Force Air Weather Service (AWS) formed a new branch whose specific purpose was monitor the sun for solar flares that could lead to a disruption on Earth with radio communications and power line transmissions. During the 1960’s, the AWS set up a network of observers in the US and in overseas locations who provided regular input to solar forecasters at the North American Aerospace Defense Command (NORAD).  In fact, by 1967, several observatories around the world were sending daily reports directly to NORAD solar forecasters.
 

Daily observations of the number of sunspots since 1 January 1900 according to Solar Influences Data Analysis Center (SIDC).  In 1967, solar cycle #20 was ramping up rapidly towards its solar maximum phase. The thin blue line indicates the daily sunspot number, while the dark blue line indicates the running annual average. The recent low sunspot activity is clearly reflected in the recent low values for the total solar irradiance. Data source: WDC-SILSO, Royal Observatory of Belgium, Brussels. Last day shown: 31 July 2018. Last diagram update: 6 August 2018.

The solar storm results in a close call
In 1967, solar cycle #20 was ramping up towards solar maximum with an increasing number of sunspots and this period is often associated with an increase in solar activity such as flares.  On May 18, 1967, observers detected an unusually large group of sunspots with intense magnetic fields on one region of the sun. By May 23rd, observers and forecasters saw the sun still appeared to be quite active and likely to produce a major solar flare. Observatories in New Mexico and Colorado actually 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.  A significant worldwide geomagnetic storm was forecast to occur within 36-48 hours, according to a bulletin from NORAD’s Solar Forecast Center in Colorado Springs, Colorado on May 23:
 

Notes recorded during May 1967 regarding the region of the sun where the major flare occurred on May 23rd. Credit: National Solar Observatory historical archive, American Geophysical Union.
 

As the solar flare event unfolded on May 23, radars at all three Ballistic Missile Early Warning System (BMEWS) sites in the far Northern Hemisphere were disrupted. These radars, designed to detect incoming Soviet missiles, appeared to be jammed. Any attack on these stations – including jamming their radar capabilities – was considered an act of war.

Retired Colonel Arnold L. Snyder, a solar forecaster at NORAD’s Solar Forecast Center, was on duty that day. The tropospheric weather forecaster told him the NORAD Command Post had asked about any solar activity that might be occurring. Along with the information from the Solar Forecast Center, NORAD learned the three BMEWS sites were in sunlight and could receive radio emissions coming from the sun. These facts suggested the radars were being ‘jammed’ by the sun, not the Soviet Union, Snyder said. As solar radio emissions waned, the ‘jamming’ also waned, further suggesting the sun was to blame, he said. 

During most of the 1960s, the Air Force flew continuous alert aircraft laden with nuclear-weapons. But commanders, thinking the BMEWS radars were being jammed by the Russians and unaware of the solar storm underway, put additional forces in a “ready to launch” status during this particular event. The Air Force did not launch additional aircraft as information from the Solar Forecasting Center made it to commanders in time to stop the military action, including a potential deployment of nuclear weapons.

A report of solar activity on May 26 from the Space Disturbance Forecast Center, a civilian forecasting center at the Environmental Science Services Administration (now NOAA).
Credit: ESSA/NOAA
 

Historic ranking among recorded solar storms
The solar flare on May 23rd, 1967 was accompanied by a coronal mass ejection (CME) which triggered a powerful geomagnetic storm that hit Earth about 40 hours later.  U.S. radio communications were disrupted in almost every conceivable way for almost a week.  In fact, this particular solar storm was so strong that the Northern Lights – normally limited to sky watchers in the high latitudes - were visible as far south as New Mexico.

The solar storm of May 1967 is ranked as one of the top in the record books. The solar storm that is known as the most powerful in recorded history is known as “The Carrington Event” which took place in September of 1859. That geomagnetic storm caused telegraph systems to fail all over North America and Europe and the northern lights were visible down to Cuba.  A "Carrington-like" solar storm today would likely be devastating given the dependence on power grids and satellite networks.

Retired U.S. Air Force officers involved in the forecasting of this solar storm describe the event in a paper that has just recently been accepted for publication in Space Weather.  This is a journal of the American Geophysical Union who provided information for this story and the abstract can be viewed here.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com