Tag Archives: auroraCast

Low Confidence in August 16, 2016 G1 Geomagnetic Watch

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Northern Lights Now – SWPC has posted a G1 geomagnetic storm watch for August 16, 2016. This means there’s the potential for aurora as Kp values could reach 5+. However, this watch comes with a caveat that it is a low confidence forecast. The forecast discussion says:

Observations from STEREO-A
revealed a solar wind speed approaching 700 km/s and Bz decreasing to -10 to -15 nT with onset, although STEREOs position differs from Earths position by about 13 degrees relative to the ecliptic.

coronal hole high speed stream is expected to become geoeffective late on 15 Aug to early on 16 Aug, although there is a chance it may pass south of the ecliptic without interacting with Earth, as WSA-Enlil suggests. At this time, confidence in the model solution is not high enough to exclude the possibility of geoeffectiveness, so the geospace forecast reflects the high speed stream influence.

So what he heck does that mean? Let’s break it down.

First the good potential news: The coronal hole is on the surface of the Sun, and as the Sun rotates, the coronal hole co-rotates. In the diagram below, this means the coronal hole high speed wind will impact the planets and satellites in a counter clockwise direction. First Earth, then B, then A then 27 days later Earth again. From the Earth’s perspective it takes 27 days for the Sun to make a complete rotation. In the diagram A and B are satellites that are designed to capture “backside” views and data from the Sun. They are called STEREO-ahead and STEREO-behind.

Current locations of STEREO Ahead and Behind
Current locations of STEREO Ahead and Behind

With these satellites, heliophysicists capture data that can be used to predict the impact of the coronal hole when it rotates towards Earth. On it’s pass by these satellites about 14 days ago, the wind stream had a strong Bz component and wind speeds of 700 km/s. Together those two factors should be enough to put on a good show.

Why the low confidence?

Take a look at the coronal hole responsible below. Notice that it is centered in the southern hemisphere of the Sun. This means it is very possible that the high speed wind will to pass to the South of Earth.

Southern Hemisphere Coronal hole imaged on August 12, 2016 by SDO
Southern Hemisphere Coronal hole imaged on August 12, 2016 by SDO

Further, the current position of the STEREO satellites puts them in a different plane than the Earth’s orbit by 13 degrees. This also means it is possible that they could be registering just the northernmost part of the CH HSS. Again, this indicates the high speed winds may go to our south.

The final comment in that discussion, “At this time, confidence in the model solution is not high enough to exclude the possibility of geoeffectiveness, so the geospace forecast reflects the high speed stream influence,” means the forecasters don’t have enough data to exclude the possibility that this may hit Earth. Keep an eye on the data! If Earth is in line for this high speed stream, and Bz stays strongly negative, aurora hunters could be in for a show. To reflect this, the NLN AuroraCast is showing the period of potential G1 storming right at the beginning of Aug 16:

G1 storming predicted in AuroraCast in the first period of August 16
G1 storming predicted in AuroraCast in the first period of August 16

Happy Hunting!

G2 Aurora storming predicted for August 2nd and August 3rd 2016

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Northern Lights Now – SWPC has issued two geomagnetic storm watches for G2 storming (KP=6+) on August 2nd and G1 storming (KP=5+) on August 3rd. These watches are the result of a pair of solar features that will impact Earth starting midday UTC on August 2nd. The NLN AuroraCast shows the current predicted timing for the timing. As always, these can be within +/- 6 hours:

Please visit NLN’s live blog of this storm and follow out Twitter feed for the most up-to-date information.

NLN AuroraCast shows the expected timing of the G1 and G2 storming for Aug 2nd and 3rd
NLN AuroraCast shows the expected timing of the G1 and G2 storming for Aug 2nd and 3rd

The first solar event that will impact Earth is the arrival of a very slow moving CME (Coronal Mass Ejection) that was launched during the July 28th filament eruption. The eruption happened almost dead center (near N01E06) on the solar disk. The associated CME was estimated to be travelling at 125-150 km/s. At that speed, it could take as many as 7 days for the CME to arrive at Earth, but it should be pushed by the ambient solar wind to 350 km/s or so. Then, an even higher wind from a coronal hole high speed wind stream should push it even faster to 600-650 km/s. There are several factors making the timing on this forecast complex – current models show the CME arriving midday to late August 2nd, 5 days after it’s launch.

In the animated GIF below watch the filament eruption in a composite of AIA 211, 193 and 171 wavelengths. These frames are about 14 hours of images taken by the Solar Dynamic Observatory (SDO) cameras. Note that just to the east (left) of the eruption, the coronal hole rotating into center disk is visible as a darker area:

AnimatedGIF of July 28th filament eruption responsible for the G2 aurora watch on Aug 2
AnimatedGIF of July 28th filament eruption responsible for the G2 aurora watch on Aug 2

The second feature is a large coronal hole that rotated into geoeffective position on July 31. The high speed stream from this CH measured at STEREO Ahead indicated that winds could reach 650-750 km/s at L1. This very strong wind will likely start impacting Earth either with or just after the CME arrives. If it “pushes” the particles in the CME, they will arrive at the leading edge of the shock. Due to the elongated shape of the CH, the period of elevated winds could be extended in duration. Here is an image of the coronal hole from SDO in AIA 211 from July 31 as it rotated toward Earth:

Coronal hole in AIA 211 from SDO on July 31
Coronal hole in AIA 211 from SDO on July 31

Together these storms have the potential to arrive with a strong shock and an extended period of high solar wind and active geomagnetic conditions. If they do, it should be a very good couple of nights for aurora hunters worldwide. As an added bonus, the Moon will be waxing just past new, so skies should be dark.

Happy Hunting!

Aurora Possible July 20 and 21

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Northern Lights Now – There is a slight chance for an aurora display on July 20 and July 21 UTC. The most likely times are in the evening, just after sunset and before moonrise, across the Northern United States. The chances aurora may be visible are higher at this time because a cloud of magnetically charged gas is moving toward Earth after an eruption on the Sun on Sunday. The chances are only slight because the cloud is moving slowly and when it arrives it may not have enough magnetic charge to activate the aurora bands. It will also be hard to see any aurora because the Moon will be full or near-full, which will make the sky fairly bright overnight.

That said – keep your cameras ready because there’s a chance!

Happy Hunting