Tag Archives: long duration

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

Winter Solstice 2015 Solar Storm Recap

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Northern Lights Now – On December 20th and 21st of 2015 the third largest geomagnetic storm of solar cycle 24 treated aurora hunters to 30 hours of dancing lights. The long duration of the storm gave nighttime photographers in North America two opportunities to see the northern lights through gaps in the clouds. Aurora reports on Twitter filled the NLN feed with images first from Wisconsin, then Alberta, Alaska, New Zealand, Northern Europe, Austria, Germany, England, Ireland, Iceland and then the North America again. Here is a chart of the official NOAA/SWPC recorded KP values from Boulder during the storm:

Boulder recorded 30 hours of G1-G2 storming during the winter solstice storm. of 2015
Boulder recorded 30 hours of G1-G2 storming during the winter solstice storm. of 2015

This solar storm started from two events on the Sun’s surface. The first was a long duration C6.69 flare at nearly dead center in the Earth strike zone. The second was a filament eruption to the south and east of the first eruption. Both events produced CMEs. Read more about the pair of eruptions NLN’s initial blog post on this storm.

Giants Causeway in Northern Ireland by Roy Smith Photo:

The CMEs from these two storms arrived later than initially predicted. Initial predictions were that the leading edge of the CME would reach Earth early in the day on December 19. The CME’s initial interplanetary shock was detected in ACE satellite data around 1520 GMT. Those 15 hours were time that many nighttime photographers wished they were sleeping instead!

Once they arrived, the two storms hit in sequence, not quite merging. As the storms played out, both had strongly negative Bz. Negative Bz is an aurora hunter’s dream. Once the field shifts south, a good show is sure to come – but we never know Bz until Earth is in the CME cloud. Space Weather scientists are still anticipate a long time before Bz can be accurately predicted in advance of a CME arrival. For now, forecasters assume arriving CMEs plasma clouds have a roughly 50/50 chance of being oriented with a Bz south.

In the Winter Solstice Storm of 2015, once the Bz shifted south, it stayed strongly south for 32 hours from 02:30GUTC on the 20th through 1030UTC on the 21st. During that time, the Bz deflection remained around -16 to -18 nT. Interestingly, after the initial shock, solar wind speeds stayed relatively low at below 450km/s for the duration of the storm. Had solar wind speeds been stronger, it’s possible that G3 level storming might have occurred. The slow wind speeds probably increased the duration of the storm (if the CME was moving faster, it would have completed it’s pass by Earth more quickly).

With a special shoutout to @VirtualAstro who helped surface some of these, here are some of our favorite images from this worldwide display of northern lights:

Swirls of green glow behind snow covered pine trees in Alaska by David W. Shaw

Green and yellow arches in the sky behind a church in Alberta by Célestine Aerden:

A string of pearls in the sky, technically called Auroral Beads, @Inukphysiker called this “lightsabors in the sky”

Another star wars reference came from Notanee Bourassa with this light-sabor aurora selfie

Team Tanner in Alberta often captures wonderful northern lights images, this anelic set was from Theresa (Tree) Tanner:

Finally, a stunning backdrop of purples and greens behind a solitary KW photography in Upstate New York:

Happy Hunting!

Pair of Solar Eruptions Prompts G2 Aurora watch for December 19, 2015

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UPDATE: 12/20/2015 2:40 PM EST

An amazing night of Aurora! It’s possible the two storms mentioned detailed in this post have merged together, producing a prolonged geomagnetic event. Storm levels have been at or above G1 (KP=5) for 15 hours. Bz has maintained a strong southward component. All signs point to another good night of aurora in northern Europe as far south as the Netherland and Germany. If you are planning to go out tonight, don’t forget the Last Minute Aurora Viewing Preparation Guide

15 hours of G1+G2 storming means many people will get to see aurora
15 hours of G1+G2 storming means many people will get to see aurora

UPDATE: 12/20/2015 1:30 AM EST

The Bz has shifted strongly south. Aurora reports are starting to come in. If the storms maintains it’s southward orientation, this is going to be a good storm.

UPDATE: 12/19/2015 10:40 PM EST

The CME has arrived at Earth. It arrived about 16 hours later than the earliest estimates. Now watch for the Bz orientation of the magnetic fields. If it stays negative, we could be in for an amazing show!

CME shock shown on space weather data charts from spaceweatherlive.com
CME shock shown on space weather data charts from spaceweatherlive.com

UPDATE: 12/18/2015 4:00 PM EST

EPAM is showing a clear rise in particles, the CME arrival is expected any moment now.

EPAM shows electron and Proton count rising as CME approaches
EPAM shows electron and Proton count rising as CME approaches

Original Post

Two eruptions on the Sun have unleashed a coronal mass ejection (CME) towards Earth. When it arrives it is expected to induce a G2 geomagnetic storm with the potential for aurora displays at mid-latitudes. The predicted timing of the arrival is good for Europe and excellent for North America. If it arrives on schedule, space weather predictions often are accurate within 3-6 hours, the northern lights show should start in Europe just before midnight, and it will be active as the Sun sets in the United States and Canada. It should last 6+ hours once it begins.

Imaging satellites in space, both ACE and SOHO, captured wonderful clear images of the eruptions. The explosions are so clear that anyone viewing them can easily identify the location and duration. In the video montage below, each view of the sun is campured through cameras with different lenses. Each sequence is roughly 80 images from SDO stitched together as a timelapse. The first, red, shows the eruptions at the 304 angstrom wavelength, followed by 335 angstroms (blue) and then 211 angstroms (purple). In each sequence the first eruptions is dead center and is from a C6.69 flare. The second is an elongated eruption to the South and East.

When flares like this occur, sometimes they eject hot plasma into space in the form of a CME. The LASCO camera aboard SOHO (Solar and Heliospheric Observatory) satellite is a specialized tool with an arm and disk in front of the lens designed to block the light coming directly from the Sun. This enables the camera to view the CME as light reflects off of it as it travels into space.

Both eruptions in the video above generated CMEs. The video below shows the raw image of the sun through lasco on the left, and then a black and white image of the difference between each set of frames coming from the those frames. The differential image makes the size and shape of the CME apparent. When the CME is mostly in one direction it means the CME is off the Earth sun line, but when the CME appears on all sides of the Sun, as is the case in this video, it indicates the CME is headed straight towards Earth. Space weather scientists can measure the speed of the CME from these images and use that estimate to predict when the CME will arrive at Earth.

What to Expect:

As of writing, the forecast is for aurora activity to begin at 21:00GMT on December 18th (4:00pm EST), and to increase over the following 6-9 hours. The NLN 3-day auroracast clock is updated two times per day, visit it for the most up-to-date forecast.

As the CME approached Earth, the first signs it is approaching will be that the EPAM rises – this happens because the approaching plasma in the CME is radiating electrons and protons. Once it arrives, the solar wind speed, the Bt and proton density, this data is available at spaceweatherlive.com, will show a sudden increase. When that happens, watch the Bz – if it is negative aurora hunters are in for a good show. Also watch the live KP. This is the best metric there is for knowing when aurora may be visible, it offers a 40-70 minute forecast. The higher the KP is the lower latitude the aurora will be visible. Here is the NLN auroracast at the time of this post:

NLN 3-day AuroraCast shows G2 storming for December 19th
NLN 3-day AuroraCast shows G2 storming for December 19th

Remember to read (and share on your social media networks!) the Last Minute Aurora Viewing Preparation Guide. This is a helpful how-to guide if you plan to go out and see the Aurora for yourself!

Happy Hunting!