We don't seem to get many auroras visible at our latitude in the UK (53N). Skyglow and just a bit too far south are the main culprits, but we did have a nice but localised (NW direction) display on 20241011.
My image from the garden with a short telephoto lens makes it appear much grander than it was.
The tree and chimney pot belong to my neighbour who is also an astronomer.
The events leading up to this follow in the timeline.
2024-10-03
AR3842 (Active Region) unleashed a X9 flare, the strongest flare of the current solar cycle. This caused a Sudden Ionospheric Disturbance (SID), an enhancement to the Earths 'D' layer, causing a partial radio blackout at HF radio frequencies. At Very Low Radio frequencies (VLF), signals are enhanced.. The flare arrived at 1215 and by 1300, the ionosphere had returned to normal indicating the flare was finished. A Coronal Mass Ejection (CME) was detected pointing towards earth. These normally take about 3 days to arrive. The shockwave from the flare is relativistic, taking about 8 minutes. The SOHO coronagraph shows the CME emerging.
SOHO LASCO C3 image courtesy NASA
This chart shows the change in signal strength received from two VLF transmitters, DHO is located in Germany, GQD is located in Cumbria, UK. The signal strength recorded (arbitrary units) is a combination of the received ground wave and received sky wave from each of the two transmitters.
The following chart shows the change in magnetic field strength measured in my back garden, well away from the road. Although it is scaled in nT (nanoTesla), the calibration is at best approximate. The magnetometer records changes in Bx (East-West orientated) and By (North-South orientated) magnetic fields.
You can see that at the same time as the Solar Flare arrival, there was also an unusual sharp disturbance in the Bx (E-W) trace on the magnetometer. The magnetometer detects disturbances in the Earth's magnetic field due to changes in the solar wind distorting the earth's magnetosphere. In this case, a shock wave associated with the flare comprising of X-Rays and intense UV.
2024-10-06
At 2024-10-06, the CME glanced the Earth resulting in an unsettled magnetic field which persisted until 2024-10-08 before slowly settling back to normal. The Aurora Borealis was visible in Northern latitudes where the sky was clear. (It wasn't clear here!).
2024-10-08
While all this was going on, a second X class flare with CME was ejected from AR3848 at 01:56 on 2024-10-08
SOHO LASCO C3 image courtesy NASA
This also captured Comet Tsuchinshan-ATLAS (C/2023 A3) as it approached the sun. Fortunately, it appeared to miss the worst of the CME.
VLF radio propagation is by the D (also known as the Daytime) layer. The D layer builds at Sunrise and dissipates at Sunset. My simple VLF receivers cannot detect SIDs that occur during night-time hours.
There was no magnetic shockwave detected, however, this may well because the magnetosphere was still being affected by the CME from 2024-10-03.
So, we have a second major CME on a collision course with Earth in a matter of days.
In the meantime, the magnetometer records that the magnetosphere is settling down.
2024-10-09
The following day, the magnetosphere was continuing to settle down (although still rather noisy/unsettled) after the first CME impact.
2024-10-10
The second CME impacted far more directly than the first, with a pre-shock at approximately 08:45UTC with the initial main impact at 15:10 UTC. A CME may take several hours to engulf and then pass by the Earth, so at 19:00 a major shift in the Bx field (taking the Bx values off scale), followed by a further shock affecting By (N-S) at 23:30 UTC. Aurora Borealis was very visible across the UK and most Northern Latitudes around the world. (Where the sky was clear!)
2024-10-11
BY 16:00, the magnetometer By trace had returned to more or less normal. Bx was still very unsettled, but also starting to return to normal values. We were lucky, we caught the tail of the visible Aurora early evening and a partial display to the North West. The only clear evening here is South Cheshire that week.
Although Auroras are wonderful phenomena to observe, the associated energy involved following a major CME impact can damage satellites, interrupt satellite communications and also impact, indirectly, the grid lines carrying power. This is one of the reasons why there are satellites (radiation hardened of course) in space that do nothing except monitor the weather on the Sun.
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