 |
| Titel |
The association of coronal mass ejections with their effects near the Earth |
| VerfasserIn |
R. Schwenn, A. Lago, E. Huttunen, W. D. Gonzalez |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 23, no. 3 ; Nr. 23, no. 3 (2005-03-30), S.1033-1059 |
| Datensatznummer |
250015200
|
| Publikation (Nr.) |
 copernicus.org/angeo-23-1033-2005.pdf |
|
|
|
|
|
| Zusammenfassung |
| To this day, the prediction of space weather effects near the Earth suffers
from a fundamental problem: The radial propagation speed of "halo" CMEs
(i.e. CMEs pointed along the Sun-Earth-line that are known to be the main
drivers of space weather disturbances) towards the Earth cannot be measured
directly because of the unfavorable geometry. From inspecting many limb CMEs
observed by the LASCO coronagraphs on SOHO we found that there is usually a
good correlation between the radial speed and the lateral expansion speed
Vexp of CME clouds. This latter quantity can also be determined for
earthward-pointed halo CMEs. Thus, Vexp may serve as a proxy for the
otherwise inaccessible radial speed of halo CMEs. We studied this connection
using data from both ends: solar data and interplanetary data obtained near
the Earth, for a period from January 1997 to 15 April 2001. The data were
primarily provided by the LASCO coronagraphs, plus additional information
from the EIT instrument on SOHO. Solar wind data from the plasma instruments
on the SOHO, ACE and Wind spacecraft were used to identify the arrivals of
ICME signatures. Here, we use "ICME" as a generic term for all CME effects
in interplanetary space, thus comprising not only ejecta themselves but
also shocks as well. Among 181 front side or limb full or partial halo CMEs
recorded by LASCO, on the one hand, and 187 ICME events registered near the
Earth, on the other hand, we found 91 cases where CMEs were uniquely
associated with ICME signatures in front of the Earth. Eighty ICMEs were
associated with a shock, and for 75 of them both the halo expansion speed
Vexp and the travel time Ttr of the shock could be determined. The
function Ttr=203-20.77*ln (Vexp) fits the data best. This
empirical formula can be used for predicting further ICME arrivals, with a
95% error margin of about one day. Note, though, that in 15% of
comparable cases, a full or partial halo CME does not cause any ICME
signature at Earth at all; every fourth partial halo CME and every sixth limb
halo CME does not hit the Earth (false alarms). Furthermore, every fifth transient
shock or ICME or isolated geomagnetic storm is not caused by an identifiable
partial or full halo CME on the front side (missing alarms). |
| |
|
| Teil von |
|
|
|
|
|
|
|
|