The transequatorial coronal hole that has been visible on the Sun since April is pointed towards Earth again today. On Each of it’s previous 4 rotations (August 12, September 8, October 4 and November 1), this coronal hole has produced solar wind in excess of 600 km/s about 3-4 days later and it has been responsible for several nice aurora displays. Here’s an image of the coronal hole during the previous four rotations and today
SWPC is anticipating the high speed stream from the CH to start arriving at Late on November 30th. Solar wind speeds will likely increase to at least 600km/s. It is likely a G1 watch will be posted for Dec 1.
An coronal mass ejection (CME) that resulted from a surprise M3.95 solar flare launched a from the Sun on Monday has prompted the NOAA Space Weather Prediction Center (SWPC) to issue a G1 geomagnetic storm watch for Veterans day and November 12th. As the CME arrives at Earth, aurora hunters may be treated to a display of northern lights further south than normal.
A G1 storm watch means that the KP, a global scale of geomagnetic and aurora activity, may reach five out on it’s 0-9 range. As the KP rises higher, aurora borealis can be seen at lower latitudes. KP=5 indicates that the lights can be seen throughout Canada, along the northern boarder of the Continental United States, Northern Europe, and southern New Zealand.
KP is notoriously hard to predict, about 50% of the time a G1 watch is in effect, the KP does not actually rise to that level, but a G1 watch also means that the KP could easily rise higher than five. If you want to know the current KP readings, your best option is to monitor live KP trackers, such as Northern Lights Now’s current live KP chart, which give an accurate KP forecast 35-70 minutes in advance.
The flare that launched the CME was a surprise. It launched from active region 2449, which had a Beta magnetic structure. Typically, active regions need to have a “delta” sunspot in their group and be classified Beta-Delta or Beta-Delta-Gamma. Nonetheless, the solar flare that launched was spectactular. Here is an animated gif of the solar region while the flare was happening. Note that this is a zoomed in image, but that the several Earths could fit in the flare area.
When flares eruptions are long duration, like this one was, they can generate CMEs. A coronal mass ejection is a cloud of solar plasma that shoots from the Sun. When a CME is moving towards Earth, it typically arrives between 2 and 4 days later. As the plasma cloud passes earth, it disrupts the magenetosphere and sends charged particles into our upper atmosphere. It is the interaction of those particles with the gases in out atmosphere that cause the dancing northern lights. Don’t worry though! This storm won’t be strong enough to have any impact at Earth’s surface – just enjoy the show!
SWPC has issued a G2 geomagnetic storm watch for October 7th and 8th and a G1 geomagnetic storm watch for October 9th. A positive polarity equatorial coronal hole will be producing a high speed solar wind that should be arriving late on Wednesday October 7th. On the previous rotation (Sept 8) this coronal hole produced a 2 day period of G1 and G2 storming. Here’s an image of the coronal hole on the previous rotation, and on the current rotation (Click for larger view):
Coronal holes on the equator of the sun take roughly 27 days to make a full rotation. During that time they are constantly changing and evolving. It is clear this coronal hole – the dark areas on the AIA 211 images above – has become larger. It is generaly a safe bet that if the previous rotation created a strong solar stream, the current rotation will as well.
Like on the last rotation, the predicted storm is coming at a good time for aurora hunters. The Moon will be in a waning crescent phase, so there shouldn’t be much light pollution from the moon. For viewers in the northern hemisphere there is between 30 and 90 minutes of additional dark hours as the nights are longer and days are shorter since the last rotation. This is what the phase of the moon should look like:
Predicting the timing of Aurora that come from a coronal holes is a little easier than that from CMEs. It is hard to determine the speed and orientation of a CME, but with a coronal hole there is a narrower window. That said, predicting the exact timing of any geomagetic storm is difficult, and predictions can be off by as much as 6-12 hours. As of this writing, the current timeline calls for a peak of the G2 storming to happen starting at the end of October 7 and continuing through the early hours of Oct 8 – with G1 storming continuing for up to 6 more hours. For the East Coast Time zone, this means Wednesday evening from sunset through 3:00-6:00AM. NLN’s current infographic for the timing of the storm’s arrival: