Magnetic environment on the shock driven by the 2012 January 27 CME

Transcription

1 Magnetic environment on the shock driven by the 2012 January 27 CME S. Yashiro 1,2, N. Gopalswamy 2, P. Mäkelä 1,2, S. Akiyama 1,2, and H. Xie 1,2 1: Catholic University of America, Washington DC, USA 2: NASA/Goddard Space Flight Center, Greenbelt, MD, USA

2 2012 January 27 Event X1.7 Flare at 17:37 UT at N27W71 Asymmetry Halo CME with a speed of 2508 km/s

3 Solar Energetic Particles The 2012 January 27 event was associated with Solar Energetic Particle (SEP) event with the peak intensity of 796 pfu.

4 Type II Radio Burst Metric DH The 2012 January 27 event was associated with a metric and DH type II radio burst.

5 Shocks in white-light coronagraph images

6 Russell and Mulligan (2002) Relation ΔR: standoff distance Rc: radius of curvature of the CME M: shock Mach number γ: adiabatic index.

7 Shocks in white-light coronagraph images

8 LASCO C2 Direct and Difference Image

9 CME and Shock Front CME Front Shock Front The leading edge seen in LASCO C2 running difference images corresponds to the shock front. We need to use proper image scale to see the CME front.

10 STEREO-A COR2 Image and a GCS flux rope fitting STEREO-COR2 image of the 2012 January 27 CME exhibiting shock-flux rope structure. The CME source was at N27E37 in STEREO-A view. The standoff distance is readily measureable from the image in (a), but it is subject to projection effects. The shock and flux rope are fitted with a spheroid and a GCS flux rope.

11 Shock and flux rope height-time The height-time plot of the shock and the flux rope (FR) at the nose direction. The difference between FR and SHK increases with time, consistent with the weakening of the shock with time. The standoff distance and the curvature if the flux rope are used as input in eq. (1) to derive Mach number.

12 How to obtain V A and B M=(Vsh-Vsw)/V A Vsh: Shock Speed Vsw: Solar Wind Speed V A : Alfven Speed Vsh can be derived from height-time measurements. Vsw can be derived from the Sheeley s formula.

13 Density Measurements form Polarized Brightness (pb) Left - pb images from STEREO-A/COR1 (a) and COR2 (b). The pb in each pixel along PA = 45 are plotted in (c) in units of mean solar brightness (MSB). The COR1 and COR2 data are combined to obtain the pb profile from 1.5 Rs to 15 Rs. The pb data are fitted by modeled pb profiles determined from the SMP and LDB density models. The data points are fit best when the multipliers are 0.4 (SMP) and 0.6 (LDB). (d) The corresponding electron density profiles with the range of multipliers as in (c). Finally, we obtain the magnetic field B upstream of the shock as

14 Magnetic Field Strength The magnetic field profile derived with γ=5/3 and the SMP density model normalized to the densities from the pb images. The error bars are from the density multiplier range. The solid curve shows a powerlaw fit to the estimated B values from eq. (3). Also shown are the empirical B profiles from Dulk and McLean (1978) and Pätzold et al. (1987) for comparison.

15 Summary & Future Works The standoff distance technique is a powerful tool to obtain the magnetic environment of the shocks from coronagraph images. The shock and flux rope are fitted with a spheroid and a GCS flux rope to avoid the projection effect. The obtained magnetic filed strength is consistent with previous results. We plan to compare the magnetic environment of CME-driven shocks causing minor (<10 pfu) and major SEP ( 10 pfu) events to better understand the CME speed SEP intensity relationship.