03/17/2015 04:00:00 UTC
Contents
Comment Section
- varSITI campaign event
- Largest geomagnetic storm at Earth for solar cycle 24, this event registered a Dst peak of -228 nT.
- Based on both the in-situ signature of the event and the ENLIL solar wind prediction for this date, I think it is likely a CIR played a role in making it so strong. There is a strong coronal hole at the South Pole and the ENLIL simulation ([[1]]) shows a fairly fast stream that interacts with the CME, and this fast speed stream (~600 km/s) shows up in ACE data as well. Based on the C2 and C3 images for the day, it appears there is a slow CME launching around noon on the 14th with a small but visible filament. On the morning of the 15th a partial halo CME, associated with a long duration flare that fell just short of M class (C9.1) and from the same active region (AR 12297), launched propagating to the East of the Sun Earth line. I think it is likely that an interaction between the CME+shock of this event and the previous blob CME, as well as the added energy from the CIR and fast speed stream behind the CME caused the severity of the geomagnetic activity at the Earth (Hess)
- This super storm is produced through a combination of effects: (1) strong magnetic field in the sheath region (> 25 nT at peak)) and ejecta (>30 nT at peak, (2) Bs field encompasses the entire duration of the ejecta, due to that the axis of the flux rope is highly inclined toward the north-south direction, (3) the interaction with CIR, and almost contained in a CIR region. Such containment by CIR prevents the expansion of the flux rope, thus makes the flux rope small in size by strong in magnetic field (Jie Zhang).
- This may be a kind of CME-CME interaction event. We have a large filament, embedded in a magnetic flux rope, close to the AR which released this highly geoeffective CME. Part of the filament (or flux rope) erupted - or at least, left the low corona - already on March 14 (around 12UT). The final and major eruption on March 15 seems to interact with the first disturbance. The interacting sectors might propagate close to Earth direction. This might be a reason for the complex in-situ signatures (two flux ropes?) as well as the increased geoeffectiveness (Manuela Temmer).
- With the ElEvo model results for the March 15 04:00 UT CME shock propagation from Sun to Earth, I need a quite low value of gamma to get the Wind speed and arrival time right, which reflects that this CME did not seem to experience much drag during interplanetary propagation. If the CME apex is really about 40° away from the Earth (as indicated by the source region position), I think its very surprising that Earth is hit by the flux rope. I think this is only possible if the flux rope had a very low inclination to the ecliptic, or as said before that there was some interaction with the CME on March 14. Maybe the drag parameter is low because the CIR was pushing from behind, adding an additional force? (Christian Moestl)
- For Christian's high inclination problem, I think that an explanation is the deflection. My theory proposed that fast CMEs deflect toward east and slow CMEs deflect toward west (Wang et al., JGR, 119, 5117, 2014). Also there are in situ signatures of such possible deflection. From fitting results of my velocity-modified flux rope model, we find there is significant propagation velocity of the CME at 1 AU which is perpendicular to the Sun-Earth line (in +y direction in GSE coordinates). (Yuming Wang)
USTC mini workshop discussion[2015/06/12]
Initiation near the Sun
Flare: raise/decay time 58 min / 6 hours
CME: Initial speed ~500 - 1000 km/s
Complex eruption. At least three different filaments involved.
Two smaller ones on the left erupted. The longer one on the right was active but not erupted.
First jet like filament eruption at the time of ~00:38UT produced a short duration C2 flare. Second filament eruption at the time of ~01:15UT (flare onset) produced the long duration C9 flare and the CME.
The source region of the flare/filament was not located near the main neutral line of the strong main bipolar region. It was located on the south west of the main active region.
Strong magnetic field cancellation observed near the source region of the second filament eruption.
There was an extended coronal hole in the south west of the active region which might be the source of the fast stream following the ICME.
Propagation in the interplanetary space
There was consensus that CME1 on the March 14 and CME2 on the March 15 were not interacted. There was no evidence of interaction in LASCO C2 and C3 images.
From Phil Hess’s measurements based on the spherical bubble model, the CME speed at 4 Rs near 02:00UT is 1100 km/s. It decelerated to 750 km/s at the 20 Rs at 05:30 UT. The propagation direction of this CME is S11W39.
From the GCS model fitting results done by USTC STEP group, the propagation direction is S11W46.
The speed at 02:00UT was 1000 km/s. When it propagated at 20 Rs near the time of 06:06UT, its speed is 720km/s.
From the USTC’s Ice Cream Cone model’s fitting results, this CME propagated with the speed of 807 km/s in the LASCO field of view. The propagation direction is S10W35. The angular width is 115 degree.
Observed transit time: 51 hours (flare onset to shock arrival) || 57 hours (flare onset to ICME arrival)
Model calculations:
Assume: CME initial speed = 800km/s
Background solar wind speed=500 km/s
Results SPM2 [Zhao et al. JGR, 2014, http://www.spaceweather.ac.cn/groupmodel.php?group=sigma ] 53 hours for shock
DMB [Bojan Vrsnak, http://oh.geof.unizg.hr/DBM/dbm.php]: 57 hours for ICME
Assume: CME initial speed = 800km/s
Background solar wind speed=400 km/s
Results: SPM2[Zhao et al. JGR, 2014, ] 60 hours for shock
DMB[Bojan Vrsnak]: 63 hours for ICME
Image Data
In-situ data
- These are in-situ plots based on the ACE daily text files, I will update them when the cdf data becomes available. In these plots the shock is very clear, but beyond that any ejecta signature is weak and there does not appear to be any strong Magnetic cloud. But there are two clear and distinct periods of strong -Bz. (Hess)
LASCO/Kanzelhöhe
Image collection of white light and chromospheric data, showing two disturbances and the partly erupted filament which is related to the CME producing AR: [link http://www.uni-graz.at/~temmerma/download/varsiti/20150315.pdf]
GOES Plot
SOHO/LASO measurement
- Height-Time plot based on SOHO/LASCO measurement
- Velocity-Time plot from SOHO/LASCO H-T measurement
- Height-Time measurement data from SOHO/LASCO: Hess_measurement.docx
Interplanetary Propagation
Christian Möstl and Tanja Rollett: ElEvo results (parameters already tweaked so it matches Wind arrivals): shock arrival at Wind: March 17 03:50 UT arrival speed 665 km/s
Wind observations (taken from the Wu et al. draft): shock arrival March 17 03:59 UT arrival speed of the sheath is 500- 600 km/s, about 100 km/s less than the ElEvo arrival speed.
This model/plot can be adjusted very easily if you think the CME initial speed, direction and launch time should be different.
initial CME parameters: inital speed at 15 Rs: 1120 km/s, at time 2015 March 15 04:00 UT, direction to Earth west 39° the speed was taken from Kevin Schenk real time email, consistent with Gopalswamy et al. proceeding; same for direction. Thus I assume that the source region position is similar to the CME direction. Because the flare happens inside the AR and there are no large coronal holes nearby, it should be relatively safe to assume this direction as the CME propagation direction. The asymmetric halo with more material to the west of the Sun also supports this. Other Parameters: background wind: 400 km/s, gamma: 0.1, ellipse aspect ratio 1.6, full width: 100° in heliospheric longitude.
Video Data
AIA 171 movie
AIA 193 movie
AIA 304 movie
AIA 1600 movie
HMI movie
C2 movie
C3 movie
References
ElEvo model: Möstl et al. 2015 Nature Communications, open access: http://www.nature.com/ncomms/2015/150526/ncomms8135/full/ncomms8135.html
