Category Archives: Alerts

Coronal Hole Prompts G2 Storm Watch for Dec 4 and 5

Share Button

Northern Lights Now – SWPC has issued a G2 geomagnetic storm watch for December 4th and 5th. Aurora activity is expected to increase as the high solar wind speeds associated with a coronal hole arrive at Earth. G2 storming means KP values above 5.67 – or strong enough to see aurora in upper mid-latitudes. The storm is arriving just after a full moon, so observation will be a little harder than normal.

The Northern Hemisphere coronal hole responsible for this activity was pointed towards Earth on December 1 and spans a relatively wide longitude. The wider than average longitude means the period of high speed winds is expected to be longer. Data from STEREO and previous rotations of this coronal hole indicate that wind speeds could be over 550 km/s for 24-36 hours and could peak above 650 km/s.

Coronal hole pointed towards Earth on Dec 1
Coronal hole pointed towards Earth on Dec 1

SWPC is currently predicting the heaviest activity at the beginning of the storm late on Dec 4 UTC (afternoon/evening for the US East coast). Typically the most aurora in a coronal hole induced storm happens at the beginning of the storm as the CIR impacts earth, then towards the end as the winds have been pushing on Earth’s magnetosphere for an extended time. This shows in the forecast as another period of G1 storming late on Dec 5. It is likely this watch will be extended into Dec 6 as a G1 watch. Here are the rough timings for the expected activity.

Predicted Aurora activity on Dec 4 and Dec 5
Predicted Aurora activity on Dec 4 and Dec 5

If you enjoyed this post please share this shortlink on Facebook and Twitter: goo.gl/3y4BPJ

Happy Hunting!

G1 Aurora Predicted for November 29

Share Button

Northern Lights Now – The combination of an arriving CIR in advance of high speed winds from a coronal hole and a glancing blow CME from a November 25 eruption have prompted SWPC to post a G1 storm watch for November 29. This means aurora will be possible with KP values in excess of 5 predicted. The forecast, and activity sources, are a little complicated, so here is a breakdown.

G1 Storm Watch is posted for Nov 29
G1 Storm Watch is posted for Nov 29

First, the recurrent coronal hole (below) pointed towards Earth on Novemeber 25 is expected to bring moderately high speed solar winds. On the previous rotation, this same coronal hole brought winds of 425-450 km/s. Data from STEREO-A, which gets hit by the solar winds from a coronal hole about a week before Earth due to it’s location, indicate the CH is now producing winds in excess of 500 km/s. As such, it is reasonable to expect winds between 500 and 600 km/s.

Southern Hemisphere coronal hole should bring a CIR and Winds in excess of 500 km/s
Southern Hemisphere coronal hole should bring a CIR and Winds in excess of 500 km/s

The leading edge of the high speed winds is often turbulent. This region, known as the CIR, is expected to arrive early on Nov 29 and this is the time that the high speed winds are most likely to induce a burst of aurora.

In addition to the coronal hole, there was an eruption on November 25 that released a CME. The majority of the CME material was launched to the East and North of Earth, but some of the released plasma cloud is predicted to arrive at Earth as a glacing blow, also on Nov 29.

CME launches from the Sun - mostly to the East and North on Nov 25
CME launches from the Sun – mostly to the East and North on Nov 25

The WSA-Enlil model, below, shows the glancing blow. Notice the areas of lighter blue and green on the upper chart. These show the areas of plasma ejected in the CME as after it has traveled most of the way to Earth. Earth, the green dot, is on the very edge of that activity with a very wispy impact around 5AM UTC.

Wispy CME is modeled as a glancing blow in WSA-Enlil
Wispy CME is modeled as a glancing blow in WSA-Enlil

These two features make the forecast difficult. It is possible they could arrive around the same time and make for a pretty amazing G2 level storm. They could also not interact much and simply make two separate periods of G1 storming. Or, the CME could miss Earth entirely and the CIR could be too weak to induce much Aurora. This is a wait and see storm, so keep an eye on the data!

Happy Hunting!

G1-G2-G1 Storm Watch for Oct 24 through October 26

Share Button

Northern Lights Now – High speed wind from the coronal hole mentioned in the previous NLN post is expected to arrive sometime on October 24 and should induce G1 and G2 storm conditions through the 26th. SWPC has issued storm watches for all three days with G1 watches on the 24th and 26th and a G2 storm watch on October 25. This means KP levels could reach 5.67 or more.

SWPC notifications timeline shows three days of storm watches posted
SWPC notifications timeline shows three days of storm watches posted

Models are predicting an extended period of elevated solar winds reaching as high as 650km/s for all three days. The initial winds will arrive with a CIR (co-rotating interaction Region) where densities are higher and the magnetic fields are more complex. This means you can monitor the progress of the arriving wind stream – it will show up as proton densities as measured at L1 by DSCOVR will rise. Once Earth is in the body of the high speed solar wind stream, density decreases and winds increase.

Current forecasts show geomagnetic activity reaching G1 levels (KP=4.67 and above) the second half of Oct 24, then reaching G2 (KP=5.67 and above) on the first part of Oct 25. Activity should slowly decline over the following 36 hours, but there may be spike of activity if the magnetic fields line up just right.

NLN AuroraCast shows three days of G1 and G2 activity from October 24-26
NLN AuroraCast shows three days of G1 and G2 activity from October 24-26

As an update to the features in that previous post, the filament did lift off, but was subsequently reabsorbed, so it did not generate a CME. The active regions rotating into view on the East limb seem to have lost their magnetic complexity. Space Weather forecasters are not expecting they will be active flare producers in the next several days.

Happy Hunting!