The first geomagnetic storming of February 2015 is now winding down.
This storm was unique in its long duration. It prompted four continuous days of G1 geomagnetic storm watches from NOAA’s Space Weather Prediction Center. This storm was also unique in that there was a long lead on predictions that there might be Aurora. The first hints there might be a storm were on Saturday, January 24th, almost a week in advance of the onset of high solar winds that prompted the watch. We noted this chance in our blog post on “How to read the WSA-Enlil Model.” By Tuesday, it was clear there was a good chance a watch would be issued as we detailed in “Next Chance for Aurora Jan 30, 2015.” The watch was finally issued Wednesday evening, for Friday.
Over the course of the storm, solar winds gradually climbed from 350-375 Km/s to a maximum peak of 783 km/s. The threshold for “very high” wind is 800km/s. The wind was coming from the co-rotating interaction region (CIR) and from the coronal hole high speed stream (CH HSS) coming off the coronal hole in the southern hemisphere of the Sun. This hole has persisted for several weeks now. As it rotates and the northern extensions cross the Earth-Sun line, Earth experiences higher solar wind speeds 3-5 days later. Keep an eye on the CH as these extensions rotate around again in two weeks.
KP readings never reached extreme levels. In fact, there was only one period with G1 storming on Feb 1 and two periods on Feb 2. [As we write this, activity has increased again and there is an outside chance we may see an additional period of G1 storming.] The main reason the storming was not more significant was a lack of proton density – with fewer protons traveling on the wind, there is less energy to displace the Earth’s magnetosphere. The periods of active storming coincided with increased proton activity. Had there been any solar eruptions that released proton solar storms along the Earth-Sun line during this period of high solar wind, we could have easily seen much stronger storming.
Even with KPs in the 4.67-5.33 range, our Twitter feed lit up with beautiful pictures of the Northern Lights and Aurora Australis. We featured the following tweets in our new Aurora Briefs Section. All of the pictures come from higher latitudes. The moon was bright and waxing gibbous, one day away from full. The peak of the storm happened just as the furthest south portion of the auroral oval was over a giant winter storm covering many viewers with a thick layer of clouds. The extra light, and lack of visibility was frustrating to many aurora viewers. This makes us appreciate the successful pictures even more! Here are were some of our favorites:
We seem to still be in an active pattern. While the current storm is winding down, we’re already looking ahead to the next potential storm. WSA-Enlil is showing increasing solar winds again with an increase in solar proton density on Friday, February 6. We’ll be keeping an eye out for stroming on that date.
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)
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:
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!
KP value readings have been between 4 and 5.33 this evening. This means possible aurora in northern Europe, Iceland, Greenland, Canada and the northern United States.
Tonight’s active space weather is primarily the result of a large coronal hole in the southern hemisphere of the Sun. It was pointed towards Earth about 3 days ago. Coronal holes elevate the solar wind speed, and higher wind speeds make geomagnetic storming more likely. Here’s an image of the coronal hole in SDO AIA 211 wavelength from December 4, 2014 – two days ago. You can see the dark area in the southern hemisphere very clearly.
Tonight that wind is arriving at Earth. We’re seeing Wind Speeds recorded at the ACE satellite of over 750 km/sec. This chart of the last two hours of solar wind speed is from SpaceWeatherLive.com as measured by the ACE Satellite.
We’ve been watching the KP flirt with storm level all evening on our Real-time live KP charts. The higher the KP goes, the more likely places further south are to see the Northern Lights.
As exciting as it is that there may be aurora tonight, there is one major factor making it hard to see the show. It is a full moon – the Cold Moon. The moon will be high and bright. Any additional light in the skies makes it harder to see the faint glow of Aurora.