Next Chance for Aurora – Friday Jan 30, 2015

Current runs of the WAS-Enlil model are showing a conditions that might be conducive to G1 geomagnetic storming this Friday. Solar winds will be high, and plasma density is expected to be moderate. Together, these imply the magnetosphere will be susceptible to, and more reactive to, arriving solar storms and geomagnetic disturbances. Earth will be on the boundary between very strong and moderate solar winds which might elevate the probability of those disturbances happening.

These elevated conditions are related to the same large Southern Hemisphere coronal hole that has been occasionally sending high speed wind speeds toward Earth over the last month. On the current WSA-Enlil run, solar winds are predicted to be 500-600 km/s. This speed implies that the material leaving the sun will arrive at Earth about 3 days later. Today is the 27th, so Earth-facing material ejected from the Sun today will arrive on the 30th. Here’s an image of the Coronal hole as of 6:00pm EST on Jan 27:

Southern Hemisphere Coronal Hole in AIA 211
Large Coronal Hole in Southern Hemisphere continues to impact Earth

Notice the hook shape dark area approaching the midpoint. It is farther North that the rest of the coronal hole. That means that high speed wind stream it is producing will be closer to the Earth-Sun plane. The high speed winds are also evident on the WSA-Enlil run. Here, we’ve freeze-framed roughly noon on the 30th. The orange area in the lower portion, and the green line in the “Radial Velocity” chart show wind speeds in excess of 500 km/s. (click for a bigger image)

WSA-Enlil output showing high speed wind
High speed winds of 500 km/s arrive at earth at noon on January 30, 2015

See our most recent post on NLN discusses how to read the WSA-Enlil output. It actually appears solar wind speed will be high for several days, the 30th is the only day showing a concurrent elevated plasma density. Thus, as of now, Friday appears to be the best chance for Northern Lights.

Plasma density may still become elevated later in the high solar winds period. An eruptive flare from active regions 2268, 2273, or 2271 in the next day could also send a solar storm towards Earth. All three regions have been growing in size and complexity over the last 24 hours. A filament eruption could also trigger a geomagnetic events. If any of those events happen, the already high wind speed could magnify the impact of even a wimpy solar storm arrival.

The predicted combination of high solar wind speed, moderate solar density, and being on the threshold between moderate and high solar wind all elevate the chances for geomagnetic storming producing Aurora on Earth on January 30. The wild card remains the Bz component, if it shifts southward, we may be in for a show. If it stays stubbornly north, we won’t see an Aurora. NLN is predicting KP of 3.6-4 with a possibility of KP=5 (G1 storming) Friday, with a chance for G1 storming through Monday if there are eruptive events. You can monitor a live chart of the current predicted KP on Northern Lights Now.

Happy hunting!

How To Read The WSA-Enlil Model Output

When there is a solar storm on its way towards Earth, or when there is a geomagnetic storm watch posted (as in the watch currently in effect), we often post an image of the WSA-Enlil model output. WSA in the name is an acronym of the three researchers who contributed to the model, Drs. Wang, Sheeley and Arge. Enlil in the name comes from the Sumerian God of wind and storms.

The model output can be confusing or disorienting at first. The following is a walk through of some features which should help in understanding how to read the output. We’ll use a snapshot of the today’s output (click for a larger view)

WSA-Enlil Model Output Jan 24, 2015
Labeled WSA-Enlil Model Output Jan 24, 2015

The two main features on this image are higher than average proton density expected to arrive this evening and the large area of high speed solar wind expected to arrive Wednesday from the southern coronal hole. We’ve labeled the image, here is a quick guide:

Label “A”: This is Earth! The left two radial graphs show the Solar System from the north think of is as “from above”, The Sun is in the center. The red and blue circles on the other side of the Sun are the two satellites (Stereo ahead and Stereo behind. At the time on the snapshot, plasma density at Earth is elevated but decreasing.

Label “B”: The two sets of graphs on the right show the data over time, the yellow bar shows the point in time the radial graphs are displaying. The plasma density, or the amount of material moving through space, is shown in the upper graph. The bottom shows the speed that material is moving as it arrives at the measurement location. Label B shows Stereo A (ahead), was seeing increased plasma density during the first part of Jan 23. The space weather at this location has no impact on geomagnetic conditions at Earth. We sometimes see people excited that the levels are increasing at this remote satelite wondering if there will be aurora – probably not, sorry.

Label “C”: This small increase in density shown is responsible for this evening’s predicted geomagnetic storm. The plasma density is elevated, you can see looking at the date along the bottom of the graph that this is likely to peak towards the end of the 24 hour period.

Label “D”: The two meridional slices (the image between the circle and the graph) show a side view of the Earth and the Sun. Above the earth is what is happening in space above our North Pole, below is the South Pole. In this image, we’ve freeze-framed the video at 19:00 UTC on 1/28, next Wednesday. There is a large area of high speed wind (orange and red) south of Earth that is coming from the Large Southern Hemisphere Coronal hole shown below in AIA 211 as the dark area.

Southern Coronal Hole on 1/24/2015 in AIA 211
Southern Coronal Hole on 1/24/2015 in AIA 211

Finally, Label “E”: This graph shows the expected solar wind speed at the same three measurement locations. This shows an increase to 500 km/s. This increase is related to the high speed wind from the coronal hole reaching a little father north. If this increase in solar wind is accompanied by an increase in plasma density because of an Earth-directed eruption on the Sun’s surface, we may see an additional geomagnetic watch and again have the possibility of seeing Aurora.

The NOAA Space Weather Prediction Center makes the WSA-Enlil model output available on their site.

Happy Hunting

“Stealth CME” Brings G3 Storm, Research Opportunity, 1/7/2015

Aurora hunters, solar weather watchers, and satellite operators experienced a surprise geomagnetic storm that registered KP=7.67 (G3 on the NOAA geomagnetic storm scale) Thursday. The storm arrived just after sunrise on January 7th for the US East coast, but allowed people in mid and western North America to see northern lights just before sunrise. Some lucky people in New Zealand saw faint aurora as dusk was setting in.

This was the strongest geomagnetic disturbance since the arrival of a CME associated with a filament eruption October 1, 2013. In total, there was a period of about 75 minutes where the KP value was above 7. At it’s peak, the ovation model was showing a wide swath of activity above most of Central and Western Canada. (click to see image larger)

G3 Geomagnetic Storming on January 7, 2015
G3 Geomagnetic Storming on January 7, 2015

The storm was nearly a complete surprise. No watches were posted in advance, and it wasn’t until nearly a day after the CME’s arrival that plausible theories were suggested as a source of the storm. It now seems likely that this “Stealth CME” was launched from an area near a large southern hemisphere coronal hole. We’ve seen CME activity correlated with coronal holes in the past. A discussion on Twitter between Dr. Tamitha Skov (@TamithaSkov) and @haloCME was the first place NLN saw this suggestion:

As the hole expanded, it may have released a CME. NLN edited a larger before/after version of the AIA 211 you can click on to see the coronal hole expansion in detail. Here, we circled the arcade hanging over the upper right portion of the coronal hole in the before image. In the after image from about 12 hours later, the hole is clearly larger, and the arcade is gone:

Before and After Coronal hole expansion
Before and After Coronal hole expansion

There are several plausible theories about why the disappearance of the arcade may have caused a CME:

  • Did the arcade lift off the sun and become the materiral of the CME as it was propelled into space?
  • Did the arcade collapse and launch a CME?
  • Was the arcade dissipation correlated but unrelated to a CME that happened as a result of the expanding coronal hole?

Events like this leave more questions than answers and are part of what make understanding space weather exciting. Studying this CME event and others like it will make for excellent doctoral theses and post-doc research projects. These research projects will expand the space weather community’s understanding of our Sun. Maybe next time we’ll predict the arrival of the next “stealth-CME” and the onset of the geomagnetic storm. Are you still looking for a PhD thesis? This might be a good place to start!

Happy Hunting!