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Title: ARE HALO-LIKE SOLAR CORONAL MASS EJECTIONS MERELY A MATTER OF GEOMETRIC PROJECTION EFFECTS?

We investigated the physical nature of halo coronal mass ejections (CMEs) based on the stereoscopic observations from the two STEREO spacecraft, Ahead and Behind (hereafter A and B), and the SOHO spacecraft. Sixty-two halo CMEs occurred as observed by SOHO LASCO C2 for the three-year period from 2010 to 2012 during which the separation angles between SOHO and STEREO were nearly 90Ā°. In such quadrature configuration, the coronagraphs of STEREO, COR2-A and -B, showed the side view of those halo CMEs seen by C2. It has been widely believed that the halo appearance of a CME is caused by the geometric projection effect, i.e., a CME moves along the Sun-observer line. In other words, it would appear as a non-halo CME if viewed from the side. However, to our surprise, we found that 41 out of 62 events (66%) were observed as halo CMEs by all coronagraphs. This result suggests that a halo CME is not just a matter of the propagating direction. In addition, we show that a CME propagating normal to the line of sight can be observed as a halo CME due to the associated fast magnetosonic wave or shock front. We conclude that the apparent widthmore » of CMEs, especially halos or partial halos is driven by the existence and the extent of theĀ associated waves or shocks and does not represent an accurate measure of the CME ejecta size. This effect needs to be taken into careful consideration in space weather predictions and modeling efforts.« less
Authors:
;  [1] ;  [2]
  1. School of Physics, Astronomy and Computational Sciences, George Mason University, 4400 University Drive, MSN 6A2, Fairfax, VA 22030, USA. (United States)
  2. The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA. (United States)
Publication Date:
OSTI Identifier:
22364270
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 799; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; MAGNETOACOUSTIC WAVES; MASS; QUADRATURES; SOLAR CORONA; SOLAR WIND; SPACE; SUN