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| Titel |
Deep Solar Activity Minimum 2007-2009: Solar Wind Properties and Major Effects on the Terrestrial Magnetosphere |
| VerfasserIn |
C. J. Farrugia, B. Harris, M. Leitner, C. Möstl, A. B. Galvin, K. D. C. Simunac, R. B. Torbert, M. B. Temmer, A. M. Veronig, N. V. Erkaev, A. Szabo, K. W. Ogilvie, J. G. Luhmann, V. A. Osherovich |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064254
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| Zusammenfassung |
| We discuss the temporal variations and frequency distributions of solar wind and
interplanetary magnetic field parameters during the solar minimum of 2007- 2009 from
measurements returned by the IMPACT and PLASTIC instruments on STEREO-A. We find
that the density and total field strength were considerably weaker than in the previous
minimum. The Alfvén Mach number was higher than typical. This reflects the
weakness of magnetohydrodynamic (MHD) forces, and has a direct effect on the solar
wind-magnetosphere interactions. We then discuss two major aspects that this weak solar
activity had on the magnetosphere using data from Wind and ground-based observations: (a)
the level of solar wind driving and the associated dayside contribution to the crosspolar cap
potential (CPCP), and (b) the shapes of the magnetopause and bow shock. For
(a) we find very weak interplanetary electric field (V xBz = -0.05 ± 0.83 mV/m)
and a CPCP of 36.6 ± 18.2 kV. The auroral activity is closely correlated to the
prevalent stream-stream interactions.We argue that the Alfvén waves in the fast
streams and Kelvin-Helmholtz instability were the predominant agents mediating the
transfer of solar wind momentum and energy to the magnetosphere during this 3-year
period. For (b) we determine 328 magnetopause and 271 bow shock crossings made
by the Cluster 1, Themis B and C spacecraft during a 3-month interval when the
daily averages of the magnetic and kinetic energy densities attained their lowest
value during the 3 years under survey. We use the same numerical approach as in
Fairfield’s (1971) empirical model and compare our findings with his classic result. The
stand-off distance of the subsolar magnetopause and bow shock were 11.8 RE and
14.35 RE, respectively, making the subsolar magnetosheath thinner by - 1RE.
This is mainly due to the low dynamic pressure which result in a sunward shift
of the magnetopause The magnetopause is more flared than Fairfield’s result. By
contrast the bow shock is less flared, and the latter is the result of weaker MHD
forces. |
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