Northern Lights Now – It’s looking like the weekend of March 23-24, 2019 will be good for Aurora hunters! A C4 flare on the Sun launched March 20th sent CME directly towards Earth. As it arrives, aurora conditions should become active. In response, SWPC has issued a G2 geomagnetic storm watch.
This story will be updated, come back soon.
Here’s a timelapse showing the Solar Storm erupting off the surface of the Sun from SDO. You will see it at roughly 11:30 coming from the active region further to the west (rightmost).
You can find the most up-to-date forecast for geomagnetic activity on the NLN 3-day forecast page. As of the time of the initial post, activity is predicted to increase the second half of March 23 and continue into the 24th.
Northern Lights Now – At Solar minimum, solar flares and active regions are infrequent, but they still happen. Active Region 2734 provides a case in point with a C1.3 solar flare eruption on March 8th that produced an earth-directed CME. As that CME arrives, aurora hunters can expect a chance for storming on March 11, and so SWPC has issued a G1 geomagnetic storm watch.
This flare had a strong “dimming” signature which is indicative of coronal propagation and a CME. What does that mean? Imagine blowing up an M-80 above the surface of a pond, you would see ripples moving out across the surface of the pond. Now imagine that the pond is boiling, you’d need a big M-80 (or a stick of dynamite!) to make ripples big enough to cross the surface. The image below shows the ripples from the flare explosion propagating across the surface of the Sun. Each frame is generated by subtracting one frame from the next, light areas show where there has been a change in brightness – or where the ripple arrived.
Notice that the ripples move out from the eruptive source in multiple directions. Because the eruption sent energy in all directions across the Sun, forecasters can assume energy was also sent off the surface of the Sun and towards Earth. This indicates the the flare was eruptive and sent a Coronal Mass Ejection (CME) into space away from the Sun and towards Earth.
The speed estimates show that the shock wave from this CME should arrive at Earth around midday on March 11 – that translates to early afternoon in Europe, late morning in the US and pre-sunrise in Australia and NZ. As a result, the forecast is for a period of G1 storming in the second half of the day. A C-class flare, even a very eruptive one, isn’t huge so the so the storming is expected to wane by early on the 12th.
Harder to Predict than Coronal Holes
Regular readers have become used to most activity recently being from coronal holes. The profile of a CME from a flare is different so we can expect a different kind of forecast. Coronal holes are fairly stable and rotate predictably with the Sun. They often last multiple rotations so Space Weather Forecasters can use data from previous rotations and from STEREO-A to make fairly detailed predictions. Solar flares are different, they happen at a point source on the Sun and the CME from each flare is oriented differently. Forecasters can make estimates of the speed of an ejection and the size, but knowing the orientation is still nearly impossible with current data.
The impact at Earth is also very different between Coronal Holes and CMEs. CH events have a distinctive signature which plays out slowly, sometimes over days, and often matches what was recorded on STEREO-A. CMEs hit with a shock, data shows a spike in solar wind speed and proton density then Bz and Bt can be used to determine the orientation of the storm. Sometimes the CME is oriented such that Bz dives deeply south for the duration of the storm providing aurora hunters a treat, sometimes is pegs north and aurora hunters get a no-show. It total though a CME related storm tends to be stronger than a coronal hole sourced storm, so forecasts will reflect a stronger storm, but it is more likely that there will be a no show. That can be frustrating for anyone who wants to plan on space weather events.
Amazing – More than 24 hours after the predicted arrival of the Feb 11 CME, space weather activity has increased. Bz just dived to -6, while Bt has been above 20 and wind speed is increasing. We may get KP=5 yet! KP is currently t 4.33, and it could easily climb over the next hour.
The interesting question presented by this data: Is this the arrival of the predicted CME, or is this a disturbance traveling along a slightly elevated wind stream?
Update: 17:30UTC Feb 15 (12:30pm EST)
We’re calling it. This storm is a miss. There is no indication that is approaching.
In the image above, if you expand it and look closely, you could almost make a compelling argument that the CME arrived between 5 and 7am GMT (during our last update) as the density is consistently above 10 p/cm3.
Time to look forward to the next potential solar storm. Luckily for aurora hunters, the wait won’t be long. On Wednesday the high speed stream from the northern extension of a southern pole coronal hole should arrive at Earth and bring with it a chance for activity. Stay tuned for a post about that.
Update: 12:30UTC Feb 15 (7:30am EST)
The CME arrival is now officialy late. It is either moving very slowly or it missed Earth. SWPC has updated their forecast and is now calling for the arrival about 6 hours from now, here’s the updated NLN 3-day AuroraCast showing the updated forecast from SWPC:
This means we’re still in wait-and-see mode. Though every hour that passes without a sure sign of the arrival means it’s more likely this was a dud.
Note in the image above a new period of G1 storming is predicted on day three. This is due to the coronal hole that was pointed towards Earth yesterday. There is a new watch posted for this period. NLN will make a new post about that watch soon.
Update: 06:00UTC Feb 15 (1:00am EST)
Over the last half hour there has been a marked increase in proton density. Readings have sustained above 10 p/cm3 with occasional spikes above 18. Earlier these reading were between 5 and 8 with occasional brief spikes. This is an indication that the CME is arriving. In addition to the proton density, Bt measurements have shown a couple abrupt changes in the last hour. Both of these indications say that the CME shock could arrive in the next hour or two, with the impact at Earth about an hour later. Here’s the current data from spaceweatherlive.com (where you monitor ACE satellite data in near real-time):
Over the next two hours, watch for more sudden jumps in Bt, proton density to increase to 20 with spikes above 30, and the solar wind speed to pick up. As the CME shock arrives, all measures should show significant changes. Once that happens, watch the Bz. If the Bz shifts into negative territory, it means the CME is oriented correctly to produce aurora on Earth. Once the Bz shifts south, about an hour later the KP will rise and aurora hunters will be rewarded for the wait tonight.
Since this storm is delayed from the predicted schedule, Europeans probably won’t get to see northern lights tonight. But people in New Zealand may get a display.
It’s time for the NLN crew to head to bed. Our next post will be in the morning.
Update: 02:30UTC Feb 15 (9:30pm EST)
Hang tight! It’s not time to give up yet. It will be at least another hour before any aurora starts, and probably more – the CME has not arrived yet. While we’re waiting, here’s some aurora from Iceland in January.
The period when KP=5+ is predicted has begun. However, NLN, space weather scientists and space weather enthusiasts are still in wait and see mode. The absence of a clear indication in EPAM of the approaching CME indicates either that the CME is missing Earth, or it is moving slower than expected. There have continued to be hints of activity in the data at ACE – recently spikes in the the proton density graphs indicate there are small waves of protons hitting the satellite. Similar to the data in the 20:00 update, these could be indicators that the front of the CME is being pushed by the high speed solar wind from the coronal hole. If that’s true, the CME may have sheared while traveling through space.
As time goes on with the arrival, confidence that there will be a northern lights display decreases. However, it is far too early to make a call that it won’t happen given the data available.
Update: 20:00UTC Feb 14 (3:00pm EST)
A slight, but sudden, increase in solar wind that happened at the same time as a drop in the Bt from 7nT to 5nT just now may indicate the first hints of the CME are starting to arrive. The next 3 hours will be telling
Update: 19:00UTC Feb 14 (2:00pm EST)
As of now, there is still no definitive indication that the CME is approaching. Fingers crossed.
A quick update on the cloud cover forecasts for this evening. In the US – it will be very clear and cold in the Northeast, this should make for great viewing conditions for aurora hunters who can handle the cold. Most of the mid-west will be mired in clouds, but there may be chances to spot the aurora through breaks in the clouds in Montana:
In Iceland – there’s a storm expected to blow through overnight. There will be a brief window where if may be clear in the early evening, but clouds are expected to roll in from the southwest to the north east. The best bet for Northern Lights in Iceland will be in the northeast, the earlier the lights start the better:
In the rest of europe – conditions look very good for most of the UK and Ireland. Scotland is predicted to have some cloud cover so it may take being flexible to find a good spot to photograph. In Norway, there could be some good views in the South, but most Scandinavian photographers will have to drive to find clear skies:
Update: 13:30UTC Feb 14 (8:30am EST)
So far, no signs that the CME is approaching on EPAM:
Typically when a CME is approaching, EPAM levels will rise slowly from the moment the eruption happens through the point that the CME shock arrives at Earth. If the EPAM isn’t rising, it can be an indication that the CME will pass by Earth without any impact. Sometimes when the CME is travelling slowly, the EPAM won’t rise until just a couple hours before the arrival. It is too early to call this storm.
Update: 00:30UTC Feb 14 (7:30pm EST 12/13)
A quick update on some of the imagery coming from the flare on 2/11. When the flare happened, there was a clear CME traveling to the north and west, but there was also a shock wave that moved eastward across the Sun showing “ripples” all the way to the coronal hole in the South West. When looking at the LASCO CME imaging, the second portion of the eruption signature shows a 3/4 partial halo. Finally, the coronal dimming is fairly extensive. All three of these together indicate there’s a good chance there is a CME headed toward Earth.