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| Titel |
Variations of Low-energy Ion Distributions Measured in the Inner Heliosheath |
| VerfasserIn |
R. B. Decker, S. M. Krimigis, E. C. Roelof |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043179
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| Zusammenfassung |
| Voyagers 1 (V1) and 2 (V2) are in the inner heliosheath (HSH) behind the termination shock
(TS). From 2004/351 (TS crossing) to 2010/012, V1 moved in helioradius over 94-112 AU at
heliographic latitude N34°, and from 2007/242 (TS crossing) to 2010/012, V2 moved over
84-91 AU at S28°. We report on variations of low-energy ion intensities, energy
spectra, and angular distributions measured in the HSH, and on the differences in such
variations observed at the V1 and V2 locations. During its first 1.5 years in the
HSH, the V2/LECP instrument measured quasi-recurrent (15-35 day) variations
in the intensities of suprathermal ions (30 keV-few MeV in 8 energy intervals).
Comparable variations have not been seen in the V1/LECP ions, which show relatively
smooth intensities. In addition, the low-energy ions at V1 have convective angular
distributions that indicate a steady decrease in the radial component of HSH plasma flow
from -55-65 km/s in mid-2007 to -10-20 km/s in late 2009. The quasi-recurrent
intensity variations at V2 can be understood in terms of what occurred on the sun a
year or so earlier, as revealed by examination of synoptic polar coronal hole maps
from GONG. Analysis suggests relations between HSH ion intensity variations
and equatorward extensions of polar coronal holes that produce stream interaction
regions in the solar wind. These interaction regions and associated enhancements of
low-energy ions accelerated at recurrent shocks can propagate into the outer heliosphere
and into the TS/HSH. The results are promising, not only in helping explain the
presence of the quasi-periodic intensity variations at V2 and the lack thereof at V1, but
also in enabling us to successfully predict the diminution of intensity variations at
V2 starting in early 2009. There are also variations in the angular distributions of
low-energy HSH ions. Large, evidently non-convective, increases in radial anisotropies
of >30 keV ions are measured at V2. During 2008.2-2008.7 these increases were
sporadic. From 2009.1-onward the radial anisotropies have been steadier and show
increasing amplitude. The onset of steady and increasing ion anisotropies is nearly
coincident with the disappearance at V2 of 0.02-1.5 MeV electrons, the onset of the
steadily decreasing radial component of plasma flow measured by V2/PLS, and
the entry of V2 into southern polar coronal hole flow as indicted by V2/MAG.
The origin of the non-convective suprathermal ion anisotropies is not yet clear. |
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