Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations

• Published in: Annales Geophysicae
• Main Authors: Amm, O., Aikio, A., Bosqued, J. M., Dunlop, M., Fazakerley, A., Janhunen, P., Kauristie, K., Lester, M., Sillanpaa, I., Taylor, M. G. G. T., Vontrat-Reberac, A., Mursula, K., Andre, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany) 2017
• Subjects: Science & Technology; Physical Sciences; Astronomy & Astrophysics; Geosciences; Multidisciplinary; Meteorology & Atmospheric Sciences; Geology; ionosphere; electric fields and currents; magnetosphere physics; current systems; plasma convection; ALIGNED CURRENT SYSTEMS; HARANG-DISCONTINUITY; ELECTRIC-FIELD; LOW-ALTITUDE; POLAR-CAP; CONVECTION; BOUNDARY; ACCELERATION; DMSP; PRECIPITATION; Svalbard; Fennoscandia
• Online Access: http://www.ann-geophys.net/21/1737/2003/; http://hdl.handle.net/2381/39442; https://doi.org/10.5194/angeo-21-1737-2003

We analyse a conjunction event of the Cluster II spacecraft with the MIRACLE ground-based instrument net-work in northern Fennoscandia on 6 February 2001, between 23:00 and 00:00 UT. Shortly after the spacecraft were located at perigee, the Cluster II satellites’ magnetic footpoints move northwards over Scandinavia and Svalbard, almost perfectly aligned with the central chain of the IMAGE magnetometer network, and cross a morning sector ionospheric shear zone during this passage. In this study we focus on the mesoscale structure of the ionosphere. Ionospheric conductances, true horizontal currents, and field-aligned currents (FAC) are calculated from the ground-based measurements of the IMAGE magnetometers and the STARE coherent scatter radar, using the 1-D method of characteristics. An excellent agreement between these results and the FAC observed by Cluster II is reached after averaging the Cluster measurements to mesoscales, as well as between the location of the convection reversal boundary (CRB), as observed by STARE and by the Cluster II EFW instrument. A sheet of downward FAC is observed in the vicinity of the CRB, which is mainly caused by the positive divergence of the electric field there. This FAC sheet is detached by 0.5°–2° of latitude from a more equatorward downward FAC sheet at the poleward flank of the westward electrojet. This latter FAC sheet, as well as the upward FAC at the equatorward flank of the jet, are mainly caused by meridional gradients in the ionospheric conductances, which reach up to 25 S in the electrojet region, but only ~ 5 S poleward of it, with a minimum at the CRB. Particle measurements show that the major part of the downward FAC is carried by upward flowing electrons, and only a small part by downward flowing ions. The open-closed field line boundary is found to be located 3°–4° poleward of the CRB, implying significant errors if the latter is used as a proxy of the former. The authors are grateful to the Principal Investigators, Henri Reme (CIS), Andr ` e Balogh (FGM), and G. ´ Gustaffson (EFW), for providing Cluster data. We like to thank R. Lepping (NASA/GSFC) and N. Ness (Bartol Research Institute) for data of the WIND and ACE satellites retrieved via CDAWeb. O.A. likes to thank the Academy of Finland for financial support. The MIRACLE network is operated within an international cooperation. Operations for the CUTLASS radar are funded by the Particle Physics and Astronomy Research Council (PPARC) and the Finnish Meteorological Institute. Research at CETP and CESR is supported by CNES (French Space Agency). Peer-reviewed Publisher Version