Spaceweather: TWO SOLAR WIND STREAMS + EQUINOX CRACKS ARE OPENING IN EARTH'S MAGNETIC FIELD

SPACEWEATHER:


TWO SOLAR WIND STREAMS: The Arctic is about to get a double dose of auroras. Two solar wind streams are approaching Earth, each flowing from a distinct hole in the sun's atmosphere. The first stream is due to arrrive on Sept. 7-8 with the second following on Sept. 11-12. Neither is expected to produce a strong geomagnetic storm. Nevertheless, Arctic lights are in the offing.


Free: Aurora Alerts.

EQUINOX CRACKS ARE OPENING IN EARTH'S MAGNETIC FIELD: The northern autumnal equinox is only 2 weeks away. That means one thing: Cracks are opening in Earth's magnetic field. Researchers have long known that during weeks around equinoxes fissures form in Earth's magnetosphere. Solar wind can pour through the gaps to fuel bright displays of Northern Lights. It just happened in Yellowknife, Canada:

"On Sept. 5-6, we could see auroras in the sky all night long, with a bright outburst
of pink shortly after midnight," says photographer Yuichi Takasaka.

During the display, a weak stream of solar wind was blowing around Earth. At this time of year, that's all it takes. Even a gentle gust can breach our planet's magnetic defenses.


This is called the the "Russell-McPherron effect," named after the researchers who first explained it. The cracks are opened by the solar wind itself. South-pointing magnetic fields inside the solar wind oppose Earth's north-pointing magnetic field. North and South partially cancel one another, opening a crack. This cancellation can happen at any time of year, but it happens with greatest effect around the equinoxes. Indeed, a 75-year study shows that September is one of the most geomagnetically active months of the year–a direct result of "equinox cracks."


Stay tuned for more Arctic lights as autumn approaches.

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