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| Titel |
Evolutionary signatures in complex ejecta and their driven shocks |
| VerfasserIn |
C. J. Farrugia, D. B. Berdichevsky |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3679-3698 |
| Datensatznummer |
250015040
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3679-2004.pdf |
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| Zusammenfassung |
| We examine interplanetary signatures of ejecta-ejecta interactions. To
this end, two time intervals of inner-heliospheric (≤1AU) observations
separated by 2 solar cycles are chosen
where ejecta/magnetic clouds are in the process of interacting to
form complex ejecta. At the Sun, both intervals are characterized
by many coronal mass ejections (CMEs) and flares.
In each case, a complement of observations from various
instruments on two spacecraft are examined in order to bring out the
in-situ signatures of ejecta-ejecta interactions
and their relation to solar observations.
In the first
interval (April 1979), data are shown from Helios-2 and ISEE-3,
separated by ~0.33AU in radial distance and 28° in
heliographic longitude.
In the second interval (March-April 2001), data from the SOHO and Wind probes
are combined, relating
effects at the Sun and their manifestations at 1AU on one of Wind's
distant prograde orbits.
At ~0.67AU, Helios-2 observes two individual ejecta which
have merged by the time they are observed at 1AU by ISEE-3.
In March 2001, two distinct
Halo CMEs (H-CMEs) are observed on SOHO
on 28-29 March approaching each other
with a relative speed of 500kms-1
within 30 solar radii.
In order to isolate signatures of ejecta-ejecta interactions, the two event
intervals are compared with expectations for pristine
(isolated) ejecta near the last solar minimum, extensive
observations on which were given by
Berdichevsky et al. (2002).
The observations from these two event sequences are then intercompared.
In both event sequences, coalescence/merging
was accompanied by the following signatures: heating of
the plasma, acceleration of the leading ejecta
and deceleration of the trailing
ejecta, compressed
field and plasma in the leading ejecta, disappearance of
shocks
and the strengthening of shocks driven by
the accelerated ejecta.
A search for reconnection signatures at the interface between the
two ejecta in the March 2001 event
was inconclusive because the measured changes in the plasma velocity
tangential to the interface (Δνt) were not
correlated with Δ(Bt /ρ).
This was possibly due to lack of sufficient magnetic shear
across the interface.
The ejecta mergers altered interplanetary parameters
considerably, leading to contrasting geoeffects despite broadly similar solar
activity.
The complex ejecta on 31 March 2001
caused a double-dip ring current
enhancement, resulting in two great storms
(Dst, corrected for the effect of magnetopause currents, <-450nT),
while the merger on 5 April 1979 produced
only a corrected Dst of ~-100nT, mainly due to
effects of magnetopause currents. |
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