Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward (B-y similar or equal to vertical bar B-z vertical bar) IMF orientation
In a case study we demonstrate the spatiotemporal structure of aurora and plasma convection in the cusp/polar cap when the interplanetary magnetic field (IMF) Bz < 0 and By ~ | Bz | (clock angle in GSM Y - Z plane: ~ 135°). This IMF orientation elicited a response different from that correspondin...
| Published in: | Annales Geophysicae |
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| Main Authors: | , , , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)
2017
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| Subjects: | |
| Online Access: | http://www.ann-geophys.net/21/539/2003/ http://hdl.handle.net/2381/39440 https://doi.org/10.5194/angeo-21-539-2003 |
| Summary: | In a case study we demonstrate the spatiotemporal structure of aurora and plasma convection in the cusp/polar cap when the interplanetary magnetic field (IMF) Bz < 0 and By ~ | Bz | (clock angle in GSM Y - Z plane: ~ 135°). This IMF orientation elicited a response different from that corresponding to strongly northward and southward IMF. Our study of this "intermediate state" is based on a combination of ground observations of optical auroral emissions and ionospheric plasma convection. Utilizing all-sky cameras at NyAlesund, Svalbard and Heiss Island (Russian arctic), we are able to monitor the high-latitude auroral activity within the ~10:00–15:00 MLT sector. Information on plasma convection is obtained from the SuperDARN radars, with emphasis placed on line of sight observations from the radar situated in Hankasalmi, Finland (Cutlass). A central feature of the auroral observations in the cusp/polar cap region is a ~ 30-min long sequence of four brightening events, some of which consists of latitudinally and longitudinally separated forms, which are found to be associated with pulsed ionospheric flows in merging and lobe convection cells. The auroral/convection events may be separated into different forms/cells and phases, reflecting a spatiotem-poral evolution of the reconnection process on the dayside magnetopause. The initial phase consists of a brightening in the postnoon sector (~ 12:00–14:00 MLT) at ~ 73° MLAT, accompanied by a pulse of enhanced westward convection in the postnoon merging cell. Thereafter, the event evolution comprises two phenomena which occur almost simultaneously: (1) westward expansion of the auroral brightening (equatorward boundary intensification) across noon, into the ~ 10:00–12:00 MLT sector, where the plasma convection subsequently turns almost due north, in the convection throat, and where classical poleward moving auroral forms (PMAFs) are observed; and (2) auroral brightening at slightly higher latitudes (~ 75° MLAT) in the postnoon lobe cell, with expansion towards noon, giving rise to a clear cusp bifurcation. The fading phase of PMAFs is accompanied by a "patch" of enhanced (~ 1 km/s) poleward-directed merging cell convection at high latitudes (75–82° MLAT), e.g. more than 500 km poleward of the cusp equatorward boundary. The major aurora/convection events are recurring at ~ 5–10 min intervals. The IMAGE magnetometer data used in this paper were collected as a German-Finnish-Polish-Norwegian project conducted by the Technical University of Braunschweig and the Finnish Meteorological Institute. The auroral observation program on Svalbard is supported by the Norwegian Research Council, AFOSR Task 2311AS, and the Norwegian Polar Research Institute. The CUTLASS radar is funded by the Particle Physics and Astronomy Research Council on grant PPA/R/R/1997/00256. SWHC and SEM are supported by PPARC Senior Fellowship PPA/N/S/2000/00197. CJF is supported by NASA grant NAG 5-2834 and NASA Living with a Star Grant Nag 5-10883. Peer-reviewed Publisher Version |
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