06/21/2015 15:30:00 UTC

Comment Section

• Compound event with a series of shocks arriving over a 3-day span, and one likely magnetic cloud arriving around midnight on the 23rd, corresponding to a clear, symmetric halo CME on the 21st which drove the strongest of the shocks with a highly compressed magnetic field. Drove a powerful geomagnetic storm with a Dst near -200 (Hess)
  
  

• WG4 EMAIL DISCUSSION ABOUT EVENT:

- July 14, 2015
This event would perfectly fit as VarSITI Campaign Event. There are a lot of interesting aspects and the observations are quite nice to track the full chain of action and reaction when interacting with Earth (maybe also interesting for other VarSITI projects, e.g. ROSMIC?). Cheers, Manuela

This is a very interesting event indeed!

The discussion of multi-step storms reminds me of this 2002 paper. It has discussion on plasma sheet effect on ring current (and Dst) and in particular shows an interesting simulation results where two earlier Bs periods were removed and its effect to the total intensity of the storm studied. It seems that removing the earlier Bs peaks did not affect significantly to the total intensity of the storm. http://onlinelibrary.wiley.com/doi/10.1029/2001JA000023/full

The strongest Bs intervals and the Dst minimum in the June event are indeed preceded by a mainly northward IMF and high density in CME sheath. Such conditions combined may have lead to particularly dense plasma sheath and enhanced the ring current later when strong Bs related to FR1 (in Ying's plot) arrived.

greetings, Emilia

- July 13, 2015
Hi Dave et al.,

Here is a plot combining Wind data and Dst. This is actually a multi-step geomagnetic storm with the global minimum of -195 nT. The first dip was produced by the fluctuating southward field components upstream of the third shock, the second one by the southward field components downstream of the third shock, and the major one by the southward field components within the ICME associated with the June 21 M2.0 eruption (01:42 UT). I agree with Nariaki that the June 22 M6.5 eruption didn't produce obvious geo-effectiveness, as you can see from the data. The fourth shock in the plot was associated with the June 22 M6.5 eruption, and it was beginning to overtake the ICME from behind at 1 AU. Another eruption on June 25 (M7.9) also produced a shock that impacted Earth (not shown in the plot), but it didn't produce geo-effectiveness either.

Also we see another 2 proceeding shocks as pointed out by Noe. These multiple preceding shocks and sheaths may precondition the magnetosphere for the growth of a strong geomagnetic storm (say, by feeding plasma to the plasma sheet). I am not sure if the third shock was propagating into a preceding ejecta, because I don't see clear ICME signatures upstream of the shock. The fluctuating southward fields upstream of the third shock may be produced by amplification of the ambient fields by the preceding shocks.

Best, Ying

On Mon, July 13, 2015 2:00 pm, Nariaki Nitta wrote: > Dave, > > I normally look for shocks rather than ICMEs on ACE RTSW data. I don't > think your M6.5 flare (on 22 June) had to do with the big Dst decrease > during 22-23 June. The CME associated with the M6.5 flare was fast but > not geo-effective (see > https://twitter.com/halocme/status/613835532116828160). Different > thoughts? > > Nariaki > > David Webb wrote on 13.07.15 13:48: > >> Nariaki, >> >> Of course I knew you would have it figured out! I guess we all need to >> get on Twitter- wonder when NOAA will start sending out "official" >> forecasts via Twitter!! Do I need to be a Twitter "subscriber" to get >> your tweets? >> >> So I assume you ID the 3 CMEs as the shock arrival times. Again let's >> be careful to differentiate shock from CME/ICME arrivals. Noe is saying >> that one of the early shocks is propagating thru a preceding CME. And >> what happened to the M6.5 event? What drove Dst to such low levels? >> >> Questions, questions, >> Dave >> >> On Mon, Jul 13, 2015 at 4:29 PM, Nariaki Nitta <nitta@lmsal.com >> <mailto:nitta@lmsal.com>> wrote: >> >> Dave, >> >> While you were preparing for SHINE, I tweeted a couple of time on >> the road (therefore no detailed image analysis). There were at least four >> eruptions during 18-22 June and the third one (associated with a M2 >> flare on 21 June) was a quite impressively circular CME >> (https://twitter.com/halocme/status/612498918639677440), which I >> think contributed the most to the geo-space effects (the CME arrived much >> earlier than I had thought). Three CMEs seemed to arrive without >> merging, see https://twitter.com/halocme/status/613216284675821568 (I >> had to adjust the time axes of the plots). As of 23 June, it looked >> possible that the Dst may hit -200 nT >> (https://twitter.com/halocme/status/613227633074028544, indeed >> auroras in California!). The M6.5 flare on 22 June was not associated >> with a very geo-effective CME even though it arrived fast. >> >> The most recent storm (13 July) was much less impressive, even its >> origin not being entirely clear. >> >> Nariaki >>

Hi Dave et al.,

The first dip on June 22nd (~-150 nT) is clearly due to a shock propagating in preceding CME, something I have been looking at recently. The larger dip on the 23rd is due to the following CME. Wind data is attached. There are three probable fast forward shocks in 30 hours from 06/21 at 15UT to 06/22 at 18UT. The third shock combines a very large increase in dynamic pressure and a large short-duration southward Bz; it must have really compressed the magnetosphere like crazy. The CME on the 23rd had extremely low density and back of the envelope estimate shows that the solar wind may have had a Mach number of ~1.

Best, Noé Lugaz

On Jul 13, 2015, at 3:26 PM, David Webb <david.webb@bc.edu> wrote:

Kyoto shows that this storm nearly reached "superstorm" (Dst<-200nT) level. http://wdc.kugi.kyoto-u.ac.jp/dst_realtime/201506/dst1506.png

Many of us may have been distracted with our preparations for SHINE. Manuela first alerted us. Do we understand the cause-effect for it? Tamitha's recent video showed that it had significant geo-effects. There were apparently a series of flares/CMEs/EPs on June 21-22. Probably the storm was driven by the M7 event on June 22 but are we sure; was it a compound event?

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Image Data

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Courtesy Ying Liu.

References

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