Browsing by Author "Hietala, H."
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- Direct observations of a surface eigenmode of the dayside magnetopauseArcher, M.O.; Hietala, H.; Hartinger, Michael D.; Plaschke, F.; Angelopoulos, Vassilis (Nature Publishing Group, 2019-02-12)The abrupt boundary between a magnetosphere and the surrounding plasma, the magnetopause, has long been known to support surface waves. It was proposed that impulses acting on the boundary might lead to a trapping of these waves on the dayside by the ionosphere, resulting in a standing wave or eigenmode of the magnetopause surface. No direct observational evidence of this has been found to date and searches for indirect evidence have proved inconclusive, leading to speculation that this mechanism might not occur. By using fortuitous multipoint spacecraft observations during a rare isolated fast plasma jet impinging on the boundary, here we show that the resulting magnetopause motion and magnetospheric ultra-low frequency waves at well-defined frequencies are in agreement with and can only be explained by the magnetopause surface eigenmode. We therefore show through direct observations that this mechanism, which should impact upon the magnetospheric system globally, does in fact occur. © 2019, The Author(s).
- Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convectionHietala, H.; Partamies, N.; Laitinen, T. V.; Clausen, Lasse B. N.; Facsko, G.; Vaivads, A.; Koskinen, H. E. J.; Dandouras, I.; Reme, H.; Lucek, E. A. (Copernicus Publications, 2012)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.