Tag Archives: auroraCast

Long Duration Aurora Event Expected Through End of October

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Northern Lights Now – A somewhat complicated aurora forecast for G1 storming Oct 22nd and 23rd kicks off what may be a long duration aurora event this week. Let’s break it down and help explain why space weather forecasters think this could be an exciting week.

First, coronal hole on the surface of the Sun rotated into the Earth strike zone on October 19. Coronal holes appear as dark areas when viewing the sun through a 211 angstom filter. This particular hole measures in as “relatively small,” but is still 20 times the size of Earth. As coronal holes rotate with the Sun, they track across the Sun’s surface from East to West or from left to right in most images you see of the Sun from satellites. The area near the center of the visible solar disk is the Earth strike zone, when coronal holes are in that area, they send high speed solar wind towards Earth. It typically arrives at Earth about 3 days later, when any disturbances or ripples in the wind have a higher than usual effect on Earths magnetosphere, prompting the possibility of aurora. Here’s an image of the coronal hole when it was in the Earth strike zone on the 19th.

Small coronal hole pointed toward Earth on October 19
Small coronal hole pointed toward Earth on October 19

Typically the best chances for aurora are at the time the higher solar wind begins, again after it has been high for a long duration, and finally when a disturbance traveling on the wind arrives. When the wind first arrives, it is carrying additional protons that it has “swept up” as it travels from the Sun to Earth. Those particles were moving towards Earth but at a slower speed. When it arrives, it appears as a sharp change in the solar wind data being read from satellites in a pattern know as an “interplanetary shock”. As the storm continues, it has a cumulative effect on the magnetosphere, “pushing it” as though it is a spring. The more compressed that spring is the more sensitive and responsive it is to regular disturbances that constantly emanate from the Sun and travel along the wind stream.

Most of the time those disturbances are small. Their sources can be seen in the normal movement in the Sun’s corona in time lapse video from sites like SDO. Occasionally, there is a larger eruption either from a flare or a filament that adds to this background activity.

On October 20, one of these larger eruptions took place in the form of a filament on the surface of the Sun erupting from an area just north of the coronal hole. The eruption launched a large cloud of plasma and particles, known as a CME or coronal mass ejection, moving toward Earth. It will arrive at Earth while the magnetosphere is still activated from the high speed wind, and so could produce an aurora show. Filament eruptions like this are stunning! This time-lapse of images from SDO shows the filament erupting over a period of about 18 hours, imagine the material flying out into space and towards Earth.

Animated GIF shows time-lapse of SDO images of filament eruption on the Sun on October 20, 2016
Animated GIF shows time-lapse of SDO images of filament eruption on the Sun on October 20, 2016

High solar wind and an arriving CME alone isn’t enough to ensure aurora. The orientation of the plasma cloud has to be just right. As of now, it is impossible to know it’s orientation until the leading edges start arriving at Earth. This means it is difficult to predict the exact timing and duration of the aurora storm. There could be none at all. When it arrives, expect proton density and Bt to increase on the DSCOVR solar wind page. If the Bz goes negative, it means the CME is oriented the right way for aurora if it goes positive or stays positive, there won’t be aurora.

A the tail end of the expected impact from the CME, Earth will fall under the influence of yet another coronal hole. This coronal hole is just rotating into the Earth Strike zone now. This one is much larger. When fully in view it will cover nearly 20% of the solar disk stretching from just south the equator to the Northern Pole of the Sun. This coronal hole has been visible every 27-28 days for the previous three rotations of the Sun. During it’s last rotation it produced 3 days of activity which occasionally reach G2 storming levels. The structure looks similar so it is likely to be equally as strong and have a similar duration. Long term forecasts are predicting there may be KP 5 through the end of the month making this an extremely long period of potential storming. NLN will be continuing to post additional updates on this coronal hole, and any events that happen near it, over the next several posts.

The large coronal hole that produced Aurora on the previous rotation is visible in the North East quadrant of the solar disk
The large coronal hole that produced Aurora on the previous rotation is visible in the North East quadrant of the solar disk

Happy Hunting

Update: G2 storming now predicted for October 14

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Northern Lights Now – In an update to NLN’s previous post, SWPC has upgrade the strom watch on October 14 from G1 to G2. This means KP values 5.67 and above are possible.

Here is the updated notifications timeline (we added the purple exclamations!)

SWPC notifications timeline shows G1 watch on 10/13 and G2 watch on 10/14
SWPC notifications timeline shows G1 watch on 10/13 and G2 watch on 10/14

And the NLN AuroraCast for days one and two showing likely time periods to expect storming conditions:

NLN AuroraCast shows periods at the end of 10/13 and beginning of 10/14 as the most likely to see strong aurora
NLN AuroraCast shows periods at the end of 10/13 and beginning of 10/14 as the most likely to see strong aurora

Don’t forget two valuable tools to use during the storm to track activity. The Live KP charts show the predicted KP over the next 30-60 minutes and you can use the DSCOVR solar wind data to get an idea for what the live KP model may predict soon (hint: more, taller bars mean likely higher KP).

Happy Hunting!

G1 Aurora Predicted for October 13 and 14

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Northern Lights Now – A small filament eruption on October 9 released a CME that is approaching Earth. It should arrive late on the 13th or early on the 14th. This CME plus a high speed stream will combine to induce aurora storming that may reach G1 levels. The means that KP is predicted to be at or above 5.00. Here is the current predicted timing from SWPC:

6 hours of G1 level storming predicted on October 13 and 14 in the AuroraCast infographic
6 hours of G1 level storming predicted on October 13 and 14 in the AuroraCast infographic

This storm is lower confidence that some other recent storms. The filament eruption was at a very northern solar latitude. Normally an eruption at this latitude would be well north of the Earth-Sun line. This one may also be off the Earth Sun line. At around the same time as the filament eruption, shown below, there was also a back-sided eruption. The partial halo CME that was visible from the back-sided eruption may have confused the models as they project the speed and path of the earth-facing CME. This will be a “wait and see” type storm. Here’s that filament eruption in AIA 193 SDO imagery:

Filament eruption is visible in this AIA 193 SDO imagery in he northeast quadrent of the solar disk
Filament eruption is visible in this AIA 193 SDO imagery in he northeast quadrent of the solar disk

Happy Hunting!