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- Lunde, J., et al.
(författare)
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Ion-dispersion and rapid electron fluctuations in the cusp : a case study
- 2008
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Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26:8, s. 2485-2502
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Tidskriftsartikel (refereegranskat)abstract
- We present results from co-ordinated measurements with the low altitude REIMEI satellite and the ESR (EISCAT Svalbard Radar), together with other ground-based instruments carried out in February 2006. The results mainly relate to the dayside cusp where clear signatures of so-called ion-dispersion are seen in the satellite data. The cusp ion-dispersion is important for helping to understand the temporal and spatial structure of magnetopause reconnection. Whenever a satellite crosses boundaries of flux tubes or convection cells, cusp structures such as ion-dispersion will always be encountered. In our case we observed 3 distinct steps in the ion energy, but it includes at least 2 more steps as well, which we interpret as temporal features in relation to pulsed reconnection at the magnetopause. In addition, fast variations of the electron flux and energy occurring during these events have been studied in detail. The variations of the electron population, if interpreted as structures crossed by the REIMEI satellite, would map near the magnetopause to similar features as observed previously with the Cluster satellites. These were explained as Alfven waves originating from an X-line of magnetic reconnection.
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- Ogawa, Y., et al.
(författare)
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Characteristics of ion upflow and downflow observed with the European Incoherent Scatter Svalbard radar
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:5, s. A05305-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated how geomagnetic activity, the solar wind (SW), and the interplanetary magnetic field (IMF) influence the occurrence of the F-region/topside ionospheric ion upflow and downflow. Occurrence of dayside ion upflow observed with the European Incoherent Scatter Svalbard radar (ESR) at 75.2 degrees magnetic latitude is highly correlated with the SW density, as well as with the strength of the IMF By component. We suggest that this correlation exists because the region where ion upflow occurs is enlarged owing to SW density and IMF By magnitude, but it does not move significantly in geomagnetic latitude. The occurrence frequency of dayside ion upflow displays peaks versus the geomagnetic activity index (Kp), SW velocity, and negative IMF Bz component; that is, ion upflow is less frequently seen at the highest values of these parameters. Dayside ion downflow in the F-region/topside ionosphere occurs only when the Kp index and/or SW velocity are high or when IMF Bz is largely negative. The ion downflow is likely due to ballistic return of the ion upflow. We suggest that the region of ion upflow not only becomes larger but also moves equatorward with increasing Kp, SW velocity, and negative IMF Bz. The ESR can so be poleward of the upflow region and observe ions convecting poleward and returning ballistically downward.
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- Ogawa, Y., et al.
(författare)
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On the source of the polar wind in the polar topside ionosphere : First results from the EISCAT Svalbard radar
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:24, s. L24103-
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Tidskriftsartikel (refereegranskat)abstract
- We present quantitative radar observations of both hydrogen ion (H+) and oxygen ion (O+) upflow in the topside polar ionosphere using measurements that were recently carried out with the EISCAT Svalbard Radar and the Reimei satellite. H+ upflow was clearly observed equatorward of the cusp above 500 km altitude. Within the cusp the H+ density was very low, and the upflow was dominated by O+ ions, but on closed field lines the H+ became the larger contributor to the upward flux above about 550 km. The total flux seemed to be conserved, and so below 550 km altitude O+ (with a small upward velocity of similar to 50 m s(-1)) appeared to determine the upward flux which was then maintained by H+! in the topside ionosphere. We also found that the H+ density in the topside polar ionosphere was several times higher than current predictions of ionospheric models like IRI2001.
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