It’s not well known, but spring and fall are prime times of year for spotting the aurora borealis in the northern hemisphere and the aurora australis in the south.
Ironically, the flare activity that typically creates geomagnetic storms and bright aurora is relatively low right now. But around each equinox in late March and September we get an aurora season due to something called the Russell-McPherron effect having to do with the geometry of Earth’s magnetic field and the solar wind.
The solar wind is the charged particles of radiation that are always flowing outward from the sun into the solar system, but it gets a boost when there is flare or a “coronal hole” in the outer layers of the sun that allows more solar wind to rush in our direction.
This week we’ve had a coronal hole and the effects of aurora season helping to open cracks in Earth’s magnetic field at the same time.
This led to an strong G3-class geomagnetic storm that wasn’t forecast early Thursday, bringing bright, early morning auroras to Montana and other northern-tier US states.
The equinox officially came earlier this week, but scientists typically note an increase in auroras within a few weeks of the official mid-point.
A moderate G2-class geomagnetic storm is forecast for tonight thanks to the same coronal hole, which means that the same northern states and northern Europe could be treated to a light show Thursday night and Friday morning.
NOAA’s Space Weather Prediction Center says the odds of a moderate storm are a bit stronger Friday, although as of this writing Thursday a moderate storm is already being observed. NOAA has issued a geomagnetic storm watch through Saturday, so be sure to keep an eye on the night sky for the next several days.
In the US, auroras tend to dip a little further south on the Atlantic Coast. A G3 storm could send Northern Lights as far south as the Washington, D.C. area. In Europe, Londoners might just get lucky too.
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