Halloween Aurora 2021 – Live Blog

Northern Lights Now – Thank you for visiting the Aurora live blog for the 2021 Halloween Aurora. Check back frequently as there are new updates for the current storm.

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NLN Live Blog Update – Saturday, October 31, 02:30 UTC (00:30 EST 10/31)
Live blog time: 6 Hours 15 mins

Happy Halloween to our EST hunters! The expected solar storm has not arrived yet. Solar wind data looks completely nominal. In fact, if you looked at only the solar wind data with 400 km/s and pretty flat data for Proton density, Bt and Bz over the last hour, you’d have no idea there was the potential for a storm.

Nominal data in the last hour at DSCOVR
Nominal data in the last hour at DSCOVR

But don’t give up yet. A quick peak at the EPAM at ACE shows that readings are still increasing. This often happens in advance of the arrival of a ICME shock. Note that they have been slowly rising since the X-class flare on the 29th. This isn’t over yet!

EPAM at ACE clearly shows there is still an inbound CME
EPAM at ACE clearly shows there is still an inbound CME

NLN Live Blog Update – Saturday, October 31, 01:00 UTC (22:00 EST 10/30)
Live blog time: 3 Hours 45 mins

Still no impact from the X-class CME. One argument in favor of it not arriving yet is the solar wind speed. After the 2 earlier impacts today, the solar wind speed only increased to the 350-400 km/s range. This wind speed would be consistent with a 4-day* transit from the Sun to Earth (as per the table below). The CME from the x-flare should be faster moving and should have wind speeds in the 650-700 km/s range. The later the ICME shock hits, the lower the wind speed should be. Based on the current wind speed it is very unlikely that the arrival late yesterday was from the X-class flare.

Wind speed to Aurora alert lead times table
Solar wind speed determines how much lead time you have to see aurora

*Hat tip to Erika Palmerio @erikapal for the 4-day transit call out on Twitter

NLN Live Blog Update – Saturday, October 31, 00:00 UTC (21:00 EST 10/30)
Live blog time: 2 Hours 45 mins

This is the point in any aurora storm where seasoned hunters start questioning the models. As of now, the arrival of the main CME is at least 6 hours past the forecast date. People who have been aurora chasing for a long time know that sometimes the storms just miss and the models are wrong. Other times the storms arrive 12-16 hours later than the forecast. It’s part of the joy of the hunt and what makes it so exciting and satisfying to see the Northern Lights when they start.

In this case the doubters have some extra evidence. First, the majority of the CME was south of the Earth-Sun plane, so it was already possible that there would only be a glancing blow. Second, it’s possible that the first two impacts from 18:30 were the flank of the main part of the storm.

Even if it misses, this storm has already been decent. The initial flank has left a prolonged period (over three hours now) of south oriented Bz. This has charged the magnetosphere and there have been reports of aurora coming in from Scotland – like the tweet below from @Cogie_s

NLN Live Blog Update – Saturday, October 30, 21:15 UTC (17:15 EST 10/30)
Live blog time: 0 Hours 0 mins

The main part of the Expected CME has not arrived yet. There have been a pair of leading front arrivals over the last three hours. These have arrived with a one and a half hour (so far) period of moderate Bz south oriented storm. This will prime the magnetosphere and bring KP=4 and potentially KP=5 (G1) aurora over the next couple hours.

In the image below, Marks for “1” are the initial leading arrival. At marker “2” a second wave of arrival hit and was associated with a shift toward a deeper Bz negative. We’ll have to wait for the storm to complete before a full analysis can be performed, but it is possible these initial two shocks are from the CMEs associated with the M-class flares that happened around the time of the X class flare.

Solar Wind Data at Start of Strom
Solar Wind Data at Start of Strom

NLN Live Blog background, Saturday, October 30, 12:00 UTC (12:15 EST 10/30)

A large x-class flare released a CME towards Earth on October 28, 2021. The CME is expected to arrive at Earth Midday Oct 30 GMT. SWPC has issued a G3 storm watch. If the CME arrives with Bz south orientation, it’s likely to bring 24-36 hours of KP=6 and KP=7 storming.

G2 and G3 storming expected over Halloween weekend
G2 and G3 storming expected over Halloween weekend

As the storm arrives, keep an eye on the Solar Wind data page. When the ICME hits, expect the solar wind speed to jump, and density and total Bt to increase. When the shock front arrives, watch the Bz closely. If it drops deeply negative, there is a very strong likelihood that there will be an aurora display. If the storm starts with a north (positive) orientation, aurora hunters will need to wait for the second phase of the arrival and the maximum potential level decreases to G2.

Happy Hunting!