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| Titel |
Coordinated polar spacecraft, geosynchronous spacecraft, and ground-based observations of magnetopause processes and their coupling to the ionosphere |
| VerfasserIn |
G. Le, S.-H. Chen, Y. Zheng, C. T. Russell, J. A. Slavin, C. Huang, S. M. Petrinec, T. E. Moore, J. Samson, H. J. Singer, K. Yumoto |
| 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. 12 ; Nr. 22, no. 12 (2004-12-22), S.4329-4350 |
| Datensatznummer |
250015094
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| Publikation (Nr.) |
 copernicus.org/angeo-22-4329-2004.pdf |
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| Zusammenfassung |
In this paper, we present in-situ observations of processes occurring at the
magnetopause and vicinity, including surface waves, oscillatory
magnetospheric field lines, and flux transfer events, and coordinated
observations at geosynchronous orbit by the GOES spacecraft, and on the
ground by CANOPUS and 210° Magnetic Meridian (210MM) magnetometer
arrays. On 7 February 2002, during a high-speed solar wind stream, the Polar
spacecraft was skimming the magnetopause in a post-noon meridian plane for
~3h. During this interval, it made two short excursions and a
few partial crossings into the magnetosheath and observed quasi-periodic
cold ion bursts in the region adjacent to the magnetopause current layer.
The multiple magnetopause crossings, as well as the velocity of the cold ion
bursts, indicate that the magnetopause was oscillating with an ~6-min
period. Simultaneous observations of Pc5 waves at geosynchronous orbit by
the GOES spacecraft and on the ground by the CANOPUS magnetometer array
reveal that these magnetospheric pulsations were forced oscillations of
magnetic field lines directly driven by the magnetopause oscillations. The
magnetospheric pulsations occurred only in a limited longitudinal region in
the post-noon dayside sector, and were not a global phenomenon, as one would
expect for global field line resonance. Thus, the magnetopause oscillations
at the source were also limited to a localized region spanning ~4h
in local time. These observations suggest that it is unlikely that the
Kelvin-Helmholz instability and/or fluctuations in the solar wind dynamic
pressure were the direct driving mechanisms for the observed boundary
oscillations. Instead, the likely mechanism for the localized boundary
oscillations was pulsed reconnection at the magnetopause occurring along the
X-line extending over the same 4-h region. The Pc5 band pressure
fluctuations commonly seen in high-speed solar wind streams may modulate the
reconnection rate as an indirect cause of the observed Pc5 pulsations.
During the same interval, two flux transfer events were also observed in the
magnetosphere near the oscillating magnetopause. Their ground signatures
were identified in the CANOPUS data. The time delays of the FTE signatures
from the Polar spacecraft to the ground stations enable us to estimate that
the longitudinal extent of the reconnection X-line at the magnetopause was
~43° or ~5.2 RE. The coordinated in-situ and ground-based
observations suggest that FTEs are produced by transient reconnection taking
place along a single extended X-line at the magnetopause, as suggested in
the models by Scholer (1988) and Southwood et al. (1988). The observations
from this study suggest that the reconnection occurred in two different
forms simultaneously in the same general region at the dayside magnetopause:
1) continuous reconnection with a pulsed reconnection rate, and 2)
transient reconnection as flux transfer events.
Key words. Magnetospheric physics (Magnetopause, cusp
and boundary layers; Magnetosphere-ionosphere interactions;
MHD waves and instabilities) |
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