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Is this solar cycle finally lifting off?
July 3, 2021: Now, Solar Cycle 25 has really begun. On July 3rd, new sunspot AR2838 produced the first X-class solar flare since Sept. 2017. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:
A pulse of X-rays ionized the top of Earth’s atmosphere, causing a shortwave radio blackout over the Atlantic Ocean: blackout map. Mariners, aviators, and amateur radio operators may have noticed unusual propagation effects below 30 MHz just after 1429 UT.
X-flares are the strongest kind of solar flare. They are typically responsible for the deepest radio blackouts and the most intense geomagnetic storms. This is the first X-flare of young Solar Cycle 25. More are in the offing. During the previous solar cycle (Solar Cycle 24) the sun produced 49 of them. Forecasters believe that Solar Cycle 25 should be at least…
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Tallbloke's Talkshop 
Graph of BoM’s aa index: Variation of Geomagnetic Activity Since 1844 (ends 1997)
https://www.sws.bom.gov.au/Educational/3/1/4
No reason given for it ending in 1997 (end of solar cycle 22?).
Look, there’s an “X” on the Sun. So that’s how those astronomers know it’s an X-class flare….
JB — yes, X-rays 😎
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Re. “The magnetic disturbance (circled in yellow) is especially rare”…
…so rare you can hardly see the circle on the graphic (see full post), but it appears to go through the ‘ti’ part of the word declination near the top.