New geoeffective parameters of very fast halo coronal mass ejections

Document Type

Article

Publication Date

5-1-2005

Abstract

We have examined the physical characteristics of very fast coronal mass ejections (CMEs) and their geoeffective parameters. For this we consider SOHO LASCO CMEs whose speeds are larger than 1300 km s-1. By examining all SOHO EIT and SOHO LASCO images of the CMEs, we selected 38 front-side very fast CMEs and then examined their associations with solar activity such as X-ray flares and type II bursts. As a result, we found that among these front-side fast CMEs, 25 are halo (or full halo) CMEs with span of 360°, 12 are partial halo CMEs with span greater than 130°, and only one is a broadside CME, with a span of 53°. There are 13 events that are shock-deflected CMEs: six are full halo CMEs, and seven are partial halo CMEs. It is found that about 60% (23/38) CMEs were ejected from the western hemisphere. We also note that these very fast CMEs have very high associations with other solar activities: all the CMEs are associated with X-ray flares (X-12, M-23, C-3), and about 80% of the CMEs (33/38) were accompanied by type II bursts. For the examination of CME geoeffectiveness, we select 12 halo CMEs whose longitudes are less man 40°, which are thought to be the most plausible candidates of geoeffective CMEs. Then we examine the relation between their CME physical parameters (mass, column density, location of an associated flare, and direction) and the Dst index. In particular, a CME direction parameter, which is defined as the maximum ratio of its shorter front from solar disk center and its longer one, is proposed as a new geoeffective parameter. Its major advantage is that it can be directly estimated from coronagraph observation. It is found that while the location of the associated flare has a poor correlation with the Dst index, the new direction parameter has a relatively good correlation. In addition, the column density of a CME also has a comparable good correlation with the Dst index. Noting that the CME column density is strongly affected by the direction of a CME, our results imply that the CME direction seems to be the most important parameter that controls the geoeffectiveness of very fast halo CMEs. © 2005. The American Astronomical Society. All rights reserved.

Identifier

20344365356 (Scopus)

Publication Title

Astrophysical Journal

External Full Text Location

https://doi.org/10.1086/428880

e-ISSN

15384357

ISSN

0004637X

First Page

414

Last Page

419

Issue

1 I

Volume

624

This document is currently not available here.

Share

COinS