Tag Archives: coronal hole

Coronal Hole Prompts Long Duration Aurora Watch Dec 7th, 8th & 9th

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Northern Lights Now – A large coronal hole that crosses the Solar equator will produce conditions conducive to aurora Thursday through Saturday this week. The expected enhanced solar winds could reach 700km/s and as a result SWPC has issued a three day G1 geomagnetic storm watch. This means KP values are likely to be enhanced and there is a good chance they will exceed KP=4.67.

G1 storm watch from SWPC has been extended to three days Dec 7 though Dec 9
G1 storm watch from SWPC has been extended to three days Dec 7 though Dec 9

This coronal hole is the return of a system that produced G1 storming on previous rotations in early October and November. Looking at the form and location of the coronal hole over the last four rotations, it is clear that it is a little farther north and bigger for this rotation. Each rotation takes about 27 days. Past experience has shown that the more of the coronal hole that passes through the center of the earth strike zone, the portion of the Solar disk pointed towards Earth, the longer the period of enhanced solar winds.

Mid September View of this month's Coronal Hole
Mid September View of this month’s Coronal Hole
Mid October View of this month's Coronal Hole
Mid October View of this month’s Coronal Hole
Early November view of this month's Coronal Hole
Early November view of this month’s Coronal Hole
Current view of this month's Coronal Hole
Current view of this month’s Coronal Hole

Close NLN readers and aurora hunters will recognize that this is a different coronal hole than the large system that has been producing storming in the second half of the month September, October and November. That system appeared to have been falling losing definition in the previous rotation, so when it rotates into view over the next couple weeks, watch it to see if it has regained organization or has continued to dissapate.

For this storm, the current expect timing of G1 storming conditions is just at the beginning of each UTC day during the watch period. The timing on these specific forecasts is difficult to predict but is often a good indicator of when it is worth keeping an eye on DSCOVR Solar wind data and the current KP.

NLN AuroraCast graphic shows the G1 periods should be at the start of each UTC day during the watch
NLN AuroraCast graphic shows the G1 periods should be at the start of each UTC day during the watch

Happy Hunting!

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

Coronal Hole Promts Aurora Storm Watch for October 22-23

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Northern Lights Now – SWPC has issued a G1 geomagnetic storm watch for October 22nd and 23rd due to the enhanced magnetic fields expected as a high speed wind stream arrives at Earth. The high winds are the result of a coronal hole pointed directly towards Earth on October 18th and 19th. The watch means it’s possible that KP values could exceed 4.67 at some point in time on each of the two days the watch is in effect. This same coronal hole was responsible for two periods of G1 storming on September 25th. Here’s an image of the coronal hole:

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

The current forecast shows the impact of this storm arriving in two waves. First, at onset there may be a shock as the high-speed wind front arrives at Earth. Later on the 23rd, another period of higher KP is expected as the cumulative effects of the high solar wind enhance the magnetosphere’s sensitivity to any disturbances traveling on the wind. In this second period, any prolonged negatively oriented Bz would push the KP higher again. That means the exact timing of the second wave will be harder to predict. Aurora hunters will need to watch the data to know when and if to go out – or as this recent Twitter meme suggests: know when to put your pants on. Here are the current predicted timings from the NLN AuroraCast:

NLN AuroraCast shows two periods of G1 storming predicted, one on the 22nd and another on the 23rd
NLN AuroraCast shows two periods of G1 storming predicted, one on the 22nd and another on the 23rd

Looking ahead a little, it’s possible to see the edges of the next coronal hole coming into view in the north and east. This is a return of the coronal hole that produced Strong aurora from September 27 to 29. The Sun rotates about once every 28 days, so this means we can expect additional geomagnetic storm watches to be posted over the next couple of days for Sept 24-26. Stay tuned for those watches too.

Happy Hunting!