Update – The storm watch has been continued to a second day. Solar wind speeds arrived later than predicted. Aurora will continue to be possible over the next 24 hours:
Northern Lights Now – SWPC has issued a geomagnetic storm watch for Thursday, February 23. This means KP values could exceed 5 with aurora visible in higher latitudes. Viewing conditions will be favorable with an almost new waning crescent Moon. The confidence on this storm is a little lower than other recent storms, but is high enough to merit a watch.
The potential aurora is due to the combination of a coronal hole that was pointed towards the Earth on February 20, and a filament eruption that produces a CME from just North of the coronal hole.
The coronal hole, pictured below, is likely to produce solar wind speeds at Earth in the 500-550 km/s range. The winds could pick up anytime between 20:00 GMT on the 22nd and 8:00am GMT on the 23rd. Once wind speeds increase, if the Bz shifts southward (negative), it will indicate northern lights activity is about to increase. Monitor solar wind speed and current Bz on NLN’s DSCOVR Solar Wind Data Page to know when aurora activity is about to increase.
The eruption was from a filament just to the north of center disk and February 19th. Watch the eruption in the animatedGIF below. The plasma cloud is visible shooting out, mostly northward, from the location of the filament. If the material from that cloud is pulled into the solar wind, it will be accelerated and pushed toward Earth. If that happened (forecasters can’t know for sure until the solar wind arrives) it could enhance the aurora activity by increasing the plasma density and accentuating the shifts in the Bz.
This is a slightly lower confidence prediction because the predicted solar wind speed is moderate, and there is a good chance that none of the plasma directed was toward Earth. The plasma may move off into space well above Earth’s North Pole. The image above showing the eruption does appear to show most of the material ejected moving to the north.
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.
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.
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.
It appears the CME missed Earth, probably to the West and North. It is unlikely at this point there will be any aurora storming tonight.
Northern Lights Now – The CME from the November 5 filament eruption is now expected to arrive at Earth late on Nov 8 and produce G1 storming. SWPC has issued a G1 geomagnetic storm watch. This forecast is lower confidence and more variable than usual. The current predicted timing shows that the period of KP=5 or higher is likely to happen at the end of the UTC day (or just after sunset on the US East coast and around midnight in Europe)
This forecast is low confidence because the majority of the CME is likely to go to the north and west of Earth. If Earth is hit, it will likely be a glancing blow. Further, it is impossible to predict the orientation of the cloud of plasma. If it happens to be oriented with a strong Bz south component, the KP could reach values higher the G1. If it is oriented with a strong positive Bz component, it’s unlikely KP values will read higher than 3 or 4. This is a classic wait-and-see storm.
Here is the WSA-Enlil model output from SWPC. It shows that when the CME arrives, it is likely to have a high proton density. This high proton density, at the same time as increasing solar wind are the primary motivations for issuing the G1 watch (click image for full size):