Auroras setting up to WOW across Northern U.S.
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Thursday, May 18, 2017, 2:00 - Keep your eyes on the northern skies on Thursday and Friday night, as they may be filled by an impressive display of the Northern Lights thanks to a speedy stream of particle from the Sun.
Space weather forecasters have issued a geomagnetic storm watch for Thursday night, anticipating a G1 (minor) geomagnetic storm, and a mixture of G2 (moderate) and G1 (minor) geomagnetic storm activity on Friday.
Credit: NOAA Space Weather Prediction Center
An excerpt from NOAA SWPC email, dated 8:35 a.m. ET, May 18. All times in the tables are displayed in UTC. Subtract 4 hours for EDT. Thus, 00-03 UT Friday is 8pm-11pm EDT Thursday.
All of this activity in Earth's magnetosphere can cause some fluctuations in our power grids, interruptions in satellite communication and GPS, and it often sparks auroras!
So, what's going on here?
Imagine, for a moment, that you could safely look past the glare of the Sun, to see what's going on near its 'surface', and furthermore that you were capable of seeing the lines of magnetism that sprout from the rolling, boiling plasmas that make up that surface. If you were to have done that on Wednesday, as NASA's Solar Dynamics Observatory did, you'd have seen this:
Credit: NASA SDO/Lockheed Martin Solar and Astrophysics Laboratory/Scott Sutherland
While much of the surface is covered in swirling plasma (the fuzzy, blotchy parts), and looping magnetic fields that help to confine those swirling plasmas and charged solar particles to the surface (the white/grey lines), one region stands out - the large dark splotch on the left, conveniently outlined by the thick dashed line.
This region is known as a Coronal Hole, and it is a place where the magnetic field lines of the Sun have opened up, leaving a large gap for plasma and solar particles to escape. While the Sun is constantly emitting a stream of particles known as the solar wind, the wind flowing out of this coronal hole is significantly faster, and is producing what's known as a Coronal Hole High Speed Stream (abbreviated CH HSS) - a ribbon of diffuse but very speed particles that is swiftly overtaking Earth in its orbit.
When that ribbon does catch up with us, on Thursday night, it is expected to have a few different impacts on our planet's magnetic field.
NOAA SWPC's WSA-Enlil solar wind forecast model, showing conditions at 03:00 UTC on Friday (11 p.m. EDT, Thursday). The two solar wind model views - density (top) and speed (bottom) - show the inner solar system from the top-down view in the circle, and side view in the cone. At this time, the green dot of Earth is now outside of a high-density region of the solar wind (top), and poised on the edge of a very fast stream of particles (bottom).
Simply due to the speed of these particles, they will all carry a lot of energy along with them, and there will be a buildup of these high energy particles right at the boundary between the slow-moving part of the solar wind we're in now, and this speedy part that's catching up to us. This is known as a Co-rotating Interaction Region (or CIR), and it alone can have a significant impact on our magnetic field, causing auroras to spring up in our northern night skies.
One other thing that these solar particles carry with them, due to the fact that they are moving charged particles, is the 'interplanetary magnetic field', and there are different 'sectors' of the solar wind that have an interplanetary magnetic field that points in a different direction. Some point in the same direction as Earth's magnetic field (and thus they repel each other), and we have fewer interactions and fewer aurora displays. Others point in the same direction as Earth's magnetic field, allowing the IMF and Earth's magnetic fields to directly interact with each other. When that happens, it makes Earth's magnetic field less effective at keeping the solar particles away from the planet.
When Earth transitions from one of these sectors to another, it's known as a Solar Sector Boundary Crossing (SSBC).
NOAA space weather forecasters were anticipating Earth encountering both the concentrated high-energy particles of the co-rotating interaction region AND the solar sector boundary crossing sometime on Thursday, ahead of the arrival of this coronal hole high speed stream (CH HSS) on Thursday night.
As of Thursday morning, however, the timing of the event has shifted some, leaving the potential for G1 geomagnetic storm activity Thursday night and the possibility of G2 (moderate) activity later in the day on Friday. While the timing may not be ideal for North America, as the strongest activity is forecast to happen during daylight hours, aurora activity can persist for some time after storm levels have diminished.
As Theresa and Darlene Tanner saw from central Alberta on Wednesday night, though, you don't necessarily need geomagnetic storm levels in order to spot the auroras.
More updates on this to come.
Source: NOAA SWPC