Aurora visible way south tonight

[QVectorman]

Based upon 3 hour K_p at peak of 7- this was a Cat G3 storm. However, it's obvious that there was strong substorming imbedded. We have seen faint aurbos down here in AZ with K values as low as high 6 for 3 hours. The storm WAS a surprise as SWPC did not call for one and when I checked the activity levels it was only a G1 storm so I went for only as high as G2 on my forecast on my homepage. Part of the reason was that this event was NOT caused by a flare triggered CME but rather a CME from a DSF (disappearing filament or an eruptive prominence) and they are harder to evaluate because they don't always cause the strong radio and X-Ray signatures of an energetic flare. Although we can observe the CMEs without other data it's not possible to evaluate their potential until they hit SOHO out about 1 million miles from us which is when we know how strong the impact is. Since the shock was travelling about 2 milliom mph this meant 30 minutes warning. Also, a 6 hour plus delay between the shock passage (which occurred around 18Z) and storm peak is not common as the first peak usually occurs during the onset phase of the storm and not the main phase.

Steve

Thanks Steve. Been waiting for your input. You always are on top of this stuff and offer excellent info

[aslkahuna]

Thanks Steve. Been waiting for your input. You always are on top of this stuff and offer excellent info

CME impacts are as tricky to forecast as is hurricane intensity for a variety of reasons. First off the origin of the CME -flare triggered ones arise in the corona while DSF or eruptive prominence ones arise in the chromosphere which is lower down denser and cooler than the corona. Hence the latter will be more massive and hit harder at a given speed. Secondly, the polarity, intensity and distribution of the imbedded magnetic fields are important since a northward pointing field will result in much less effect as will a weak total field. Unfortunately, this information we do not have available until the CME reaches ACE and SOHO about a million miles out. However, had I not gone off my computer before the 00Z Gemag observations, I probably would have posted an urgent post in this Forum. In this case the total field was 20 nT with the southward component equal to the whole field at times when the storm was peaking hence we got the maximum possible effect . Finally,there is the question of how the magnetosphere and auroral oval will respond to the impact. A while back we had a K=8 G4 storm that barely brough aurorae visible in the northern states and here we had a G3 storm bring aurora down to Alabama. Chris Schur in Payson AZ photographed a faint glow but it was too low and faint to be seen from here in Tucson.

Steve

[BeauDodson]

Based upon 3 hour K_p at peak of 7- this was a Cat G3 storm. However, it's obvious that there was strong substorming imbedded. We have seen faint aurbos down here in AZ with K values as low as high 6 for 3 hours. The storm WAS a surprise as SWPC did not call for one and when I checked the activity levels it was only a G1 storm so I went for only as high as G2 on my forecast on my homepage. Part of the reason was that this event was NOT caused by a flare triggered CME but rather a CME from a DSF (disappearing filament or an eruptive prominence) and they are harder to evaluate because they don't always cause the strong radio and X-Ray signatures of an energetic flare. Although we can observe the CMEs without other data it's not possible to evaluate their potential until they hit SOHO out about 1 million miles from us which is when we know how strong the impact is. Since the shock was travelling about 2 milliom mph this meant 30 minutes warning. Also, a 6 hour plus delay between the shock passage (which occurred around 18Z) and storm peak is not common as the first peak usually occurs during the onset phase of the storm and not the main phase.

Steve

Great information! Seems like there was a lack of information during and immediately after the event. You need an email list! Would love to receive notifications.

Thanks for the info!