Credits Henry Wismayer is a writer based in London.
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EXETER, United Kingdom — It was an overcast morning in southwest England, but Kirk Waite was staring at the sun. In the open-plan forecasting room of the Met Office, the U.K.’s national meteorological agency, the country’s senior weather-watchers were monitoring low-pressure systems sweeping in from the Atlantic and across the British Isles. Waite was studying weather of a very different sort.
He sat at a crescent-shaped desk arrayed with computer monitors displaying real-time images of our local star. Generated by the Solar Dynamics Observatory (SDO), a NASA satellite that has been taking second-by-second snapshots of the sun since 2010, the images had been processed by a spectral filter to display the solar surface in a range of lucent wavelengths measured in angstroms (Å).
At 6,173 Å, the sun appeared as a mostly featureless sphere with a couple of rogue blemishes: active sunspots that showed high levels of electromagnetic activity. The most spectacular projection was 171 Å, which depicted the star in the deep ultraviolet range. At this wavelength, it was an explosive yellow orb encircled by a chaotic nimbus of sunbursts and looping streamers. For around six years, the sun has been in what is called Solar Cycle 25, and the tumult shown at 171 Å was characteristic of the “solar maximum,” its most turbulent phase, which commenced last October.
This morning, Waite, the on-duty forecaster at the Met’s Space Weather Observation Centre (MOSWOC), was scrutinizing sunspot number 3998, an archipelago of blotches around four times the Earth’s diameter. On his central monitor, he brought up a greenish image of the sun at 94 Å, highlighting radiation in the X-ray range, and toggled the timestamp back around 24 hours to display 3998 just as it erupted in a torpedo-shaped expulsion of light. This was a solar flare, a massive discharge of radiation and solar energetic particles (SEPs).
Next, Waite turned to a pair of projections, each with a black circle overlaying the solar disc. These were coronagraphs, images taken from another observation platform stationed around a million miles from Earth. The spokes of light emanating from the disc showed the solar wind, a constant flow of ionized particles streaming off the sun’s visible surface, or photosphere, at a rate of one million tons per second.
But sun-watchers like Waite are more preoccupied by the more intermittent crescendos, outbursts with the explosive power to reach Earth with unusual velocity and volume. These can be divided into two distinct but intertwined phenomena: solar flares and coronal mass ejections (CMEs).
Orbital sensors had determined that the flare Waite showed me was an M3.3 — moderate but worth keeping an eye on. “It lasted around two hours, quite a long duration, which is often a sign that a CME might follow,” Waite said. Sure enough, a couple of hours later, the coronagraphs showed a blast of matter exploding from the right “limb” of the photosphere. Waite’s task during his 12-hour shift was to forecast “space weather” — to monitor these two types of solar eruptions and to predict their potential impact on Earth.
Using a mouse cursor, Waite lassoed the outer limits of the CME. Scrolling forward a few minutes — the ejection now greatly expanded — he drew another. The time-lapse between the two would provide an estimate of the CME’s ejection speed (this one was travelling at almost 800 miles per second), from which computer modelling could extrapolate an estimate of the eruption’s volume, density and its likelihood of hitting Earth.
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