First radiation dose measurements from an aircraft during an extreme geomagnetic storm

First radiation dose measurements from an aircraft during an extreme geomagnetic storm

LOS ANGELES. Space Environment Technologies (SET) reported that it has made the first radiation dose measurements above 8 km (26,000 ft) on a high latitude continental U.S. (CONUS) air traffic route during an extreme geomagnetic storm. Dr. W. Kent Tobiska, SET’s Chief Scientist, reported that the company’s Automated Radiation Measurements for Aerospace Safety (ARMAS) Flight Module 7 (FM7) instrument was used to make continuous measurements during the 11½ hour flight.

The storm was a NOAA scale G5 event and occurred on May 10-11, 2024 (Figure 1). It is now being called the Gannon Superstorm of 2024 to honor Jenn Gannon, who passed away unexpectedly on May 1, 2024. She was an internationally respected space weather physicist who, among other firsts, developed the real-time U.S. magnetic field network MagStar system for Computational Physics, Inc. (CPI) to observe ground induced currents (GIC). GIC are a space weather hazard for the power grid. She was also the Chair of the American Commercial Space Weather Association (ACSWA) and served on the PROSWIFT Act (2020) Space Weather Advisory Group (SWAG), where she contributed advice across many industrial sectors related to mitigating the hazards of space weather to U.S. Government agencies.

The Gannon Superstorm occurred while the ARMAS FM7 detector was measuring dose on a non-stop San Francisco to Paris flight May 10-11, 2024 (Figure 2). This flight normally flies north from San Francisco to very high latitudes over Canada’s Hudson Bay, across Greenland, above the London, and down to Paris on a “great circle route.” This is the shortest distance between two points on a globe.

Typically, this flight would take place at 11–12 km altitude (37,000 – 40,000 ft) and reach latitudes >70N geographic. However, prior to the flight, air traffic control (ATC) determined that there may be communication outages and excessive radiation hazard during the storm on that route. Instead, they rerouted the flight across northern CONUS, over Boston, and on to Paris. The ATC system rerouted the flight corridor to not only lower latitudes and but lower altitudes, with the maximum altitude only 10 km (36,000 ft). The penalty for lower latitudes and lower altitudes was only an added half hour. This is because the plane took advantage of a very strong tailwind across the Atlantic as reported by the pilots to the passengers. At one point, the plane’s ground speed was 1111 kph (700 mph).

Tobiska noted, “what could have easily been the equivalent of 2–3 chest X-rays exposure for us (a chest X-ray is approximately 100 micro-Sieverts) was instead only 81 micro-Sieverts – less than one chest X-ray.” The total dose accumulated during the flight (Figure 3) was also recorded as a dose rate (Figure 4), where the 1-minute variability in the weather of the radiation environment was elevating the dose rate above the 6 micro-Sievert/hour baseline.

The baseline dose rate comes from neutrons and protons at aircraft altitudes that are created by galactic cosmic rays. The variability above the baseline has been suggested to come from precipitating energetic electrons being scattered from the Van Allen radiation belts and cause secondary gamma-rays measured in the aircraft. It is still an area of active scientific research.

“These remarkable measurements,” Tobiska said, “are the first time that measurements in an aircraft have occurred during an extreme geomagnetic storm. We see multiple processes occurring here and these data will be used for generations to validate scientific models of atmospheric radiation.” An extreme geomagnetic storm is defined by NOAA as a G5 level event, analogous in scale to a category 5 hurricane.

Tobiska also reported that the ARMAS data “are serving as a foundation for radiation weather that will eventually be reported by ATC to pilots. This single flight unambiguously showed that radiation exposure can be easily managed by flying lower latitudes and lower altitudes during storms, in a manner analogous to diverting around major thunderstorms. By taking advantage of favorable jet stream winds, there was almost no penalty in flight time, either!”

A photo taken from the plane’s exit door window during the height of the storm, when the flight was south of Nova Scotia (lights visible) at 10 km (36,000 ft), is shown in Figure 5. Tobiska noted, “the seasoned pilots, one of whom lives in Alaska, told me after the flight that it was the most intense auroral display he has ever seen during a flight. He showed me his personal pictures of brilliant streaming corona aurora directly over the plane that was taken from the cockpit window.”