ON HALO CORONAL MASS EJECTIONS OBSERVED BY LASCO DURING 1996-2012

English Abstract:

We present an investigation of halo coronal mass ejections (CMEs) to understand the origin of halo CMEs which is very important because halo CMEs are regarded as main causes of heliospheric and geomagnetic disturbances. In this study, we have investigated 313 halo CMEs observed during 1996-2012 by LASCO, coronal holes (CHs) and solar flares to understand the origin of halo CMEs. On investigation of 313 halo CMEs and related solar flares and coronal holes data we find that all 313 halo CMEs were observed when there were CHs and solar flares within 10° to 60° and 128 (40.8%) and 73 (23.6%) halo CMEs were observed when there were CHs and solar flares within 10° and 20°, respectively. The speed of halo CMEs are deceases with increase of distance between halo CMEs associated solar flare location and boundary CHs. The speed of halo CMEs also increases with importance of solar SXR flares. The speed of halo CMEs does not increases with increase of area of CHs while the solar winds speed increases with increase of CHs area. The halo CMEs may be of two types: accelerated halo CMEs and decelerated halo CMEs. We are of the view that the halo CMEs may have been produced by some mechanism, in which the mass ejected by solar flares or active prominences, gets connected with the open magnetic lines of CHs (source of high speed solar wind streams) and moves along them to appear as a halo CMEs, earlier suggested by Verma and Pande (1989) and Verma (1998, 2002). The various results obtained in the present analysis are discussed in the light of existing scenario of heliospheric physics.

References: 

Verma, V. K. & Pande, M. C. 1989, in Proc. IAU Colloq. 104 ” Solar and Stellar Flares” (Poster Papers), Stanford University, Stanford,  p.239

Verma, V. K. 1998, Journal of Indian Geophysical Union, 2, 65

Verma, V. K. 2002, COSPAR Colloquia Series(Elsevier Science Ltd), 13, 319