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.
Northern Lights Now – SWPC has posted a G1 storm watch for January 24. Active space weather could make for an aurora display starting on the 23rd as high speed winds from a coronal hole buffet Earth’s magnetosphere.
The northern hemisphere coronal hole was directed towards Earth on January 21 as shown below in an image from the SDO satellite. Coronal holes emit higher solar wind speeds and it takes 2-4 days for those winds to arrive at Earth.
The timing of this storm is expected to be at the beginning of the UTC on the 24th. For people in the UK, the storm should start around midnight and go into the wee hours. For north american hunters, it should start just after Sunset. These forecasts can be off by as much as 6 hours. If the wind speed is higher than expected, the storm will start earlier as the wind arrives sooner (but the show should be better)
Here is the official graphic from SWPC (Space Weather Prediction Center)