Characteristics of interplanetary magnetic clouds in relation to their solar association

Details Characteristics of interplanetary magnetic clouds in relation to their solar association Characteristics of interplanetary magnetic clouds in relation to their solar association

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999jgr...104..581b&link_type=abstract

Journal of Geophysical Research, Volume 104, Issue A1, p. 581-592

Physics

6

Interplanetary Physics, Interplanetary Physics: Ejecta, Driver Gases, And Magnetic Clouds

Scientific paper

Interplanetary magnetic clouds (MCs) are always associated with a coronal mass ejection. In some particular cases, they also have been related to the occurrence of near-surface solar events such as filament eruptions and flares. In this paper we use a sample of 67 MCs observed between 1967 and 1982 at 1 AU to obtain better statistics of their near-surface solar association, considering Hα flares, filament eruptions, X-ray events, and coronal holes. We also study possible differences in the characteristics of the clouds depending on their solar association. We find that 57% of the MCs observed at 1 AU were associated with flares (F), 21% were associated with filament eruptions (P), 7% were associated with both (FP), and 15% were not associated with any reported near-surface solar event. Most of the associated flares occurred at the west of the solar central meridian, and most of the associated filament eruptions occurred at the east. In 95% of the cases for which the coronal hole information was available, a nonpolar coronal hole was near the region of the solar event. In the cases where the cloud was not associated with a flare or filament eruption, a coronal hole was always near the solar central meridian. This suggests that coronal holes may be playing a role in the formation of interplanetary magnetic clouds. We consider the spatial profiles of magnetic field and plasma parameters inside MCs, observed as temporal variations as clouds pass detectors at 1 AU. The average magnitudes of these parameters inside the cloud were also considered. The profiles observed were the following: flat (A-type), with a maximum (B-type), descending (C-type), ascending (D-type), with a minimum (E-type), fluctuating (F-type), and with two minima (G-type). We find that the most common profiles and the average values of the different parameters vary for different solar associations. We also find some correlations between the cloud parameters, which may appear different in clouds associated with F or P. However, as there is a fraction of MCs not associated with near-surface solar events, it is possible that this kind of activity is not essential for the formation of an interplanetary magnetic cloud, but only adds particular characteristics to the clouds.

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