| 1. |
- Hietala, H., et al.
(författare)
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Supermagnetosonic subsolar magnetosheath jets and their effects : from the solar wind to the ionospheric convection
- 2012
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:1, s. 33-48
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF) may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1) the jets could have a scale size of up to a few RE but less than similar to 6 R-E transverse to the XGSE axis; (2) the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3) during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.
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| 2. |
- Waara, Martin, 1980-, et al.
(författare)
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Oxygen ion energization observed at high altitudes
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus Publications on behalf of the European Geosciences Union. - 0992-7689 .- 1432-0576. ; 28, s. 907-916
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Waara, M., et al.
(författare)
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Oxygen ion energization observed at high altitudes
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 28:4, s. 907-916
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Tidskriftsartikel (refereegranskat)abstract
- We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 R-E) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2-0.4 R-E in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization.
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| 4. |
- Laitinen, T. V., et al.
(författare)
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Local influence of magnetosheath plasma beta fluctuations on magnetopause reconnection
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus Publications. - 0992-7689 .- 1432-0576. ; 28:5, s. 1053-1063
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from two subsolar Cluster magnetopause crossings under southward interplanetary magnetic field and strong mirror mode fluctuations in the magnetosheath. In both events the reconnection outflow jets show strong variations on the timescale of one minute. We show that at least some of the recorded variations are truly temporal, not spatial. On the same timescale, mirror mode fluctuations appear as strong magnetic fluctuations in the magnetosheath next to the magnetopause. This suggests that mirror modes can cause the variations either through modulation of continuous reconnection or through triggering of bursty reconnection. Using a theoretical scaling law for asymmetric reconnection we show that modulation of reconnection at a single x-line can explain the observations of the first event. The second event cannot be explained by a single modulated x-line: there the evidence points to patchy and bursty reconnection.
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| 5. |
- Motoba, T., et al.
(författare)
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In situ evidence for interplanetary magnetic field induced tail twisting associated with relative displacement of conjugate auroral features
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A04209-
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Tidskriftsartikel (refereegranskat)abstract
- We provide in situ evidence for a twisted near-Earth tail configuration that is responsible for the time sequence of conjugate auroral features associated with relative interhemispheric displacement during a weak substorm, as reported by Motoba et al. (2010). We analyzed the magnetic field data observed using four Cluster satellites in the vicinity of 11-14 R-E central downtail, in close conjunction with the Iceland-Syowa conjugate optical auroral features. Interestingly, we found that the variations in the magnetic field y component (B-y) at all satellites correlated moderately well with the variations in the time-shifted interplanetary magnetic field (IMF) clock angle (theta(CA)). The correlation coefficients (0.56 similar to 0.61) between the B-y field at Cluster and IMF theta(CA) peaked at a time delay of 52 +/- 1 min from the dayside magnetopause, probably corresponding to the time scale for the reconfiguration of the IMF theta(CA) related B-y field in the near-Earth tail. The IMF theta(CA) related B-y variation at Cluster, regarded as a manifestation of the twisting magnetotail configuration, also roughly coincided with the relative magnetic local time displacement of nightside conjugate auroral forms. These results provide strong evidence that the reconfiguration (twisting) process of the near-Earth tail on a relatively longer time scale controls the nightside conjugate auroral locations in both ionospheres.
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