Saturday, March 23, 2024

We're Having an Equinox Geomagnetic Storm

Well, not exactly the equinox, that was the night of the 19th, but it's still pretty close to the equinox and the day/night terminator line (the gray line) is close to due north/south. In other words, close enough.

What appears to have started it is that at this the time of year we get what are called "equinox cracks" in the Earth's magnetic field. Researchers have long known that during a few weeks either side of the equinoxes fissures form in Earth’s magnetosphere. Solar wind can pour through the gaps. At best, they produce bright aurora displays. The solar wind flowing through those cracks appears to be what's behind the current G2 class geomagnetic storm. 

This morning (UTC - it was around 0130 UT or 9:30 PM eastern on the 22nd), the sun produced an X1 class solar flare from two different sunspot groups. AR3614 and 3615 exploded in tandem, directing their fire straight at Earth.  The coronal mass ejection from that flare is supposed to reach Earth in early hours of Monday, the 25th (again, early morning UTC, so Sunday evening on the East coast).  AR3614 is the top (Northern) group.

Flares that occur in pairs like this are not unheard of but are not as common as those from a single sunspot group. 

Researchers have long known that widely-spaced sunspots can explode in tandem. They're called "sympathetic solar flares." (.pdf alert) Occasionally, magnetic loops in the sun's corona fasten themselves to distant pairs of sunspots, allowing explosive instabilities to travel from one to the other. This has apparently happened to AR3614 and AR3615.

Those with tons of experience watching videos of sympathetic solar flares like this say this one wasn't as good as some they've seen, but "close enough."

While the current Aurora forecasts don't indicate they'll become visible in the lower 48 states, the K index is approaching 6 and that makes me think those in the northernmost states might get to see one; and remember that the CME is forecast to reach Earth Sunday night to Monday morning. Ignoring the equinox cracks for the moment, for the auroras to be seen from the lower 48, the dip in magnetic latitude in the middle of the country has a dramatic effect on the K index and magnetic storm levels needed to make them visible. 

G is the geomagnetic storm level (currently 2) and the K index is currently 5.7.  I'd expect areas between the green and yellow curves should be able to see the Aurora. 


  1. I'm cross-posting this to Virtual Mirage. I hope you don't mind.

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