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Biggest Ever Solar Flare Just Got Bigger

Biggest Ever Solar Flare Just Got Bigger: Otago Research

Space Physics researchers force rethink of eruption’s true size-

University of Otago physicists have shown that November's record-breaking solar explosion was much larger than its official estimate, thanks to innovative research using the upper atmosphere as a gigantic X-ray detector. Their findings have been accepted for 17 March publication in Geophysical Research Letters, published by the American Geophysical Union.

On 4 November last year, the largest solar flare ever recorded exploded from the Sun's surface, sending an intense burst of radiation streaming towards the Earth. Before the storm peaked, X-rays overloaded the detectors on the satellites, forcing scientists to estimate the flare's size.

Taking a different route, Otago researchers used radio wave-based measurements of the X-rays' effects on the Earth's upper atmosphere to revise the flare's size from a merely huge X28 to a "whopping" X45**, say Space Physics researchers Associate Professor Neil Thomson, Dr Craig Rodger and Emeritus Professor Richard Dowden. “This makes it more than twice as large as any previously recorded flare, and if the accompanying particle and magnetic storm had been aimed at the Earth, the damage to some satellites and electrical networks could have been considerable,” says Associate Professor Thomson.

Their calculations show that the flare’s X-ray radiation bombarding the atmosphere was equivalent to that of 5000 suns, though none of it reached the Earth’s surface, the researchers say.

At the time of the flare, the researchers were probing the ionosphere** with radio waves as part of a long-term research programme. Their new measurement comes from observations of the indirect effects of the increased X-ray radiation on Very Low Frequency (VLF) radio transmissions across the Pacific Ocean from Seattle, North Dakota and Hawaii to their receivers in Dunedin.

“Increases in X-rays enhance the ionosphere causing its lowest region to decrease in height, which in turn affects the phase of VLF transmissions. Our previous research shows that these phase shifts are proportional to the number of kilometres by which the ionosphere is lowered,” says Associate Professor Thomson.

Because the height by which it lowers is known to relate directly to the amount of X-ray radiation present, the team could then make a new measurement of the flare’s size, the researchers say.

“We were at the right place, at the right time with the right knowledge – which was based on nearly 15 years of work by staff and students in the Physics Department’s Space Physics Group,” says Associate Professor Thomson. The research would not have been possible without data provided by the US National Oceanic & Atmospheric Administration Space Environment Centre, which came up with the initial X-28 estimate, he added. 2/… “We used their solar measurements to calibrate the response of the atmosphere to X-rays, so when this event overloaded the satellite detectors we were in a unique position to make this measurement. Given that any future flares are unlikely to be large enough to overload the ionosphere, we believe that our new method has great advantages in determining their size in the event of satellite detector overloads,” he says.


Scientists classify solar flares according to their brightness in the X-ray wavelengths. There are three categories:

X-class flares are big; they are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere which can damage or destroy satellites. The biggest solar flare on record before 4 November 2003 was an X20.

M-class flares are medium-sized; they generally cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare.

Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth.

The ESA/NASA satellite SOHO webpage has images of the great solar flare at: One image taken by the EIT instrument (Extreme ultraviolet Imaging Telescope), shows overloading of this satellites ultraviolet camera by the solar flare:

The Ionosphere is the region of the earth's atmosphere where ionisation caused by incoming solar radiation affects the transmission of radio waves. It normally extends from a height of 70 to 400 kilometres above the surface.

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