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

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!