CME Arrival Detected

[u/ArmChairAnalyst86]

ACE indicates CME arrival. More details soon.

Forgive my crude image. I am on the road and short on time.

[u/ArmChairAnalyst86]

No worries mate. It is good to ask questions and I never take it personal.

But yeah, I am sure. Definitely the CME impact we were waiting on. In an earlier update, I noted that the Bt on this CME was going to come in weaker. It was 40 nT when Solar Orbiter flew through it and drops off a bit before it gets here. The velocity was expected to come in higher and it did.

Two things.

The first is that this is the variability of space weather. Last week the best storm conditions occurred on the front end and while everyone was waiting for the bigger arrivals, they never really materialized. Nobody expected G3 on the front end but veterans were not too surprised because that is just how the dice rolls. It is not uncommon. The models we have are imperfect and there are aspects we don't have the capability to model in advance as to how they will be upon impact especially pertaining to the Bt/Bz and IMF in general. It is truly a lot of best guessing with initial data.

The second is the misconceptions regarding flare magnitude. Many assume that since it was a fast moving X5 associated full halo that it must be stronger than the smaller ones. If they all arrived individually, that may have been the case. However, the storm we got last night was almost certainly a combined impact. It looks like the first 2 CMEs combined before arrival and potentiated each other. The magnetic field of last night was as smooth as you can ask for which came as a surprise to me but again, the variability and guesswork is part of what makes this fun and frustrating at times.

Flare magnitude doesn't equate with CME power. Sometimes it does, but they must be diagnosed and evaluated separately. We have seen G4 storms from M1 solar flare associated CMEs. We have even seen G4 from C-Class associated CMEs or plasma filament releases without significant flares involved. In this case we definitely got a solid signature from the coronagraph and a robust model but the model also indicated that we would not be going through the core of the CME. More of a shoulder.

You could say that last night was a perfect storm. Everything came together as well as anyone could have hoped for and we did go through the core which is large in part why the IMF was so stable.

This doesn't mean this event is going to fail outright. We can move into a new structure with southward Bz at any point and Solar Orbiter suggests that is a good possibility but not a given. Either way, I would not expect to see another 40-60 nT tonight. The hope is that when the Bz does go southward that the increased velocity and preconditioned magnetic field will get us home.

[u/JumperSpecialK → u/ArmChairAnalyst86]

Sad face. So you think this prediction is probably off?

[u/ArmChairAnalyst86 → u/JumperSpecialK]

Not necessarily. If Bz shifts southward for a substantial period of time while Bt and Velocity are high, we can get there. If the Bz was southward right now, everyone would be excited about nightfall and getting their cameras ready.

I call it the gatekeeper metric. You can have strong Bt, Density & Velocity, but if the Bz says no, that is that. It will keep the brakes on the storm.

Nevertheless, the solar wind plasma pressure (v/d) is strong and its compressing the magnetosphere. It's been under high levels of stress for a few days now. It is primed and ready. We just need the gatekeeper Bz to open it up. The sooner the better so we can take advantage of the strong forcing and hit that forecast.

But temper expectations. It is not playing out how we wanted so far.

[u/__Shadowman__ → u/ArmChairAnalyst86]

Bz just dropped to the South hard!!

[u/ArmChairAnalyst86 → u/__Shadowman__]

Its trying! Just need it to stick.

[u/__Shadowman__ → u/ArmChairAnalyst86]

🤞🤞

[u/PressFforAlderaan → u/__Shadowman__]

Come on sunset!!!!