M6.9 solar flare on Aug. 25 produced CME; model indicates possible impact on Aug. 28 and increased auroras
The Sun emitted an M6.9 flare from active region 4513 on Aug. 25, associated with a coronal mass ejection (CME) that models show may graze Earth on Friday, Aug. 28; there was an R2 radio blackout and the effect may be re…
Cover image: NASA — Public domain, via Wikimedia Commons.
The Sun produced an M6.9 flare on 25 August from sunspot (active region) 4513, which also launched a coronal mass ejection (CME). The explosion — one of five M-class flares recorded from the same region in the previous 24 hours — caused a moderate radio blackout (R2) over parts of the sunlit hemisphere. Initial models indicate the CME could deliver a glancing blow to Earth on the morning of Friday, 28 August, with an expected arrival around 6–7 a.m. EDT (10:00–11:00 GMT) and an uncertainty margin of roughly seven hours.
Details of the flare, blackout and model forecast
The M6.9 flare peaked at 6:00 a.m. EDT (10:00 GMT) on 25 August, according to records cited by Space.com and the monitor SpaceWeatherLive. Active region 4513 had been highly active in the prior 24 hours, producing multiple M-class flares.
The event also triggered a radio blackout classified as R2, which affected high-frequency communications over parts of Africa, Europe and the Arctic on the sunlit side of Earth, according to the same monitoring sources.
Initial NASA model runs (M2M WSA-ENLIL+Cone), cited by Space.com, project that the CME may strike Earth marginally — a "glancing blow" — on the morning of 28 August (around 10:00–11:00 GMT), with an estimated arrival uncertainty of +/-7 hours. Aurora hunter Jure Atanackov described the CME as slow and, taken alone, "not very promising."
Impacts already observed and conditions forecast for 27–28 August
The directly confirmed effect so far is the R2 blackout, which degrades high-frequency communications in the regions noted. That impact occurred on the hemisphere that was sunlit at the time of the flare, according to available records.
In addition to the CME associated with the M6.9 flare, the Solar Influences Data Analysis Center (SIDC) forecasts that a high-speed solar wind stream originating from a positive-polarity coronal hole should begin influencing Earth from 27 August. The SIDC indicates that this stream could leave geomagnetic conditions "unstable to active," with a chance of minor storm levels.
Thus, the situation for 28 August involves two key uncertainties: the exact arrival time of the CME, given the model's margin of error, and the development of the high-speed solar wind predicted by the SIDC.
How the effects could combine to boost auroras
If a glancing impact from the CME coincides in time with the arrival of the high-speed solar wind stream forecast by the SIDC, the two effects could add together and amplify geomagnetic activity. That would raise the likelihood of auroras becoming more visible, possibly at lower latitudes than usual.
A determining factor for the intensity of the geomagnetic response is the magnetic orientation of the CME on arrival: a strongly southward magnetic component tends to couple more efficiently with Earth's magnetic field and increase activity levels.
Although Atanackov characterized the CME as slow and, alone, "not very promising," he and the cited models note that combination with the fast solar wind could change that assessment — with the outcome dependent on the uncertainties already mentioned.
Updates needed and confirmed facts
In the coming days the crucial information will be: (1) refinement of the CME arrival time by modeling centers; (2) determination of the CME's magnetic orientation as it approaches Earth's vicinity; and (3) monitoring of the onset and strength of the high-speed solar wind stream expected from 27 August. These variables will define the potential for increased auroras and impacts on communications.
The facts confirmed so far, according to the cited sources, are: an M6.9 flare from active region 4513 on 25 August; emission of an associated CME; an R2 radio blackout recorded over areas of the sunlit hemisphere; and the SIDC's forecast of influence from a high-speed solar wind beginning on 27 August.
Projections remain subject to timing and magnetic-orientation uncertainties; forecasts will be updated by space monitoring centers in the days leading up to 28 August.
Sources consulted:
- Space.com — https://www.space.com/stargazing/auroras/sun-fires-powerful-m6-9-solar-flare-and-cme-toward-earth-could-it-boost-northern-lights-chances-this-week
