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| Titel |
Periodic traveling compression regions during quiet geomagnetic conditions and their association with ground Pi2 |
| VerfasserIn |
A. Keiling, F. S. Mozer, H. Rème, I. Dandouras, E. Lucek, M. Fujimoto, H. Hasegawa, G. D. Reeves |
| 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 ; 26, no. 11 ; Nr. 26, no. 11 (2008-10-21), S.3341-3354 |
| Datensatznummer |
250016275
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3341-2008.pdf |
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| Zusammenfassung |
| Recently, Keiling et al. (2006) showed that periodic (~90 s) traveling
compression regions (TCRs) during a substorm had properties of Pi2
pulsations, prompting them to call this type of periodic TCRs "lobe Pi2".
It was further shown that time-delayed ground Pi2 had the same period as the
lobe Pi2 located at 16 RE, and it was concluded that both were remotely
driven by periodic, pulsed reconnection in the magnetotail. In the study
reported here, we give further evidence for this association by reporting
additional periodic TCR events (lobe Pi2s) at 18 RE all of
which occurred in succession during a geomagnetically very quiet,
non-substorm period. Each quiet-time periodic TCR event occurred during an
interval of small H-bay-like ground disturbance (<40 nT). Such disturbances
have previously been identified as poleward boundary intensifications
(PBIs). The small H bays were superposed by Pi2s. These ground Pi2s are
compared to the TCRs in the tail lobe (Cluster) and both magnetic pulsations and
flow variations at 9 RE inside the plasma sheet (Geotail). The main results of this study are:
(1) Further evidence is given that periodic TCRs in the tail lobe at
distances of 18 RE and ground Pi2 are related phenomena. In particular, it
is shown that both had the same periodicity and occurred simultaneously
(allowing for propagation time delays) strongly suggesting that both had the
same periodic source. Since the TCRs were propagating Earthward, this source
was located in the outer magnetosphere beyond 18 RE. (2) The connection of
periodic TCRs and ground Pi2 also exists during very quiet geomagnetic
conditions with PBIs present in addition to the previous result (Keiling et
al., 2006) which showed this connection during substorms. (3) Combining (1)
and (2), we conclude that the frequency of PBI-associated Pi2 is controlled
in the outer magnetosphere as opposed to the inner magnetosphere. We propose
that this mechanism is pulsed reconnection based on previous results which
combined modeled results and observations of substorm-related periodic TCRs
and ground Pi2. (4) We show that TCRs with small compression ratios (ΔB/B<1%)
can be useful in the study of magnetotail dynamics and we
argue that other compressional fluctuations with ΔB/B<1%
(without having all of the characteristic signatures of TCRs) seen in the
tail lobe could possibly be related to the same mechanism that generates TCR
with ΔB/B>1% (which are more commonly studied). (5) Finally, it
is noted that both quiet time and substorm-related periodic TCRs had
remarkably similar periods in spite of the drastically different geomagnetic
conditions prevailing during the events which poses the important question
of what causes this periodicity under these different conditions. |
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