09/30/2012 23:00:00 UTC

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Comment Section

  • Complex ejecta at 1 AU (J. Zhang)
    • strong B
    • possibly multiple CMEs interacting; need to check all halo CMEs in the plausible launch window
  • C. Moestl: maybe two ICMEs, the shock of the 2nd travels through the first one
  • simulations of these events?

“On 2012 September 30-October 1 the Earth underwent a two-step geomagnetic storm. We examine the Sun-to-Earth characteristics of the coronal mass ejections (CMEs) responsible for the geomagnetic storm with combined heliospheric imaging and in situ observations. The first CME, which occurred on 2012 September 25, is a slow event and shows an acceleration followed by a nearly invariant speed in the whole Sun-Earth space. The second event, launched from the Sun on 2012 September 27, exhibits a quick acceleration, then a rapid deceleration, and finally a nearly constant speed, a typical Sun-to-Earth propagation profile for fast CMEs. These two CMEs interacted near 1 AU as predicted by the heliospheric imaging observations and formed a complex ejecta observed at Wind, with a shock inside that enhanced the pre-existing southward magnetic field. Reconstruction of the complex ejecta with the in situ data indicates an overall left-handed flux-rope-like configuration with an embedded concave-outward shock front, a maximum magnetic field strength deviating from the flux rope axis, and convex-outward field lines ahead of the shock. While the reconstruction results are consistent with the picture of CME-CME interactions, a magnetic cloud-like structure without clear signs of CME interactions is anticipated when the merging process is finished.” (Abstract from Lui et al. (2014).

Image Data

In-Situ Data

A combination of SWEPAM and MAG data from the ACE Satellite:
Plot sw mag plasma 2012093000.png Plot sw mag 2012093000.png Plot sw vel 2012093000.png
The blue lines are an approximation of the CME cloud and the red line denotes the shock.

Heliospheric Imaging

De-projected Height Time Plots of the shock and ejecta fronts as obtained from the GCS (measured by Hess) (for GCS details, see Thernisien 2006) along with velocity and acceleration profiles determined from the Aerodynamic Drag Model.

20120928stack.png

Fitting parameters in GCS Model: Carrington Longitude: 167.087 degrees, Latitude: 16.7706 degrees, Tilt Angle: -68.7582 degrees, Aspect Ratio: .326671, Half Angular Width: 33.2613

GOES X-RAY FLUX

20120928 goes.png

The GOES X-ray Flux of the flare associated with the event. The vertical line approximately denotes the flare peak time.

Video Data

COR2A
COR2B
HI1A
HI1B
HI2A
HI2B

References

Lui, L et al., 2014, ApJL, 793 L41