Multi-instrument study of the dynamic cusp during dominant IMF B-y conditions

• Published in: Annales Geophysicae
• Main Authors: Khan, H., Lester, M., Davies, J. A., Milan, S. E., Sandholt, P. E.
• 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; ionosphere-magnetosphere interactions; particle precipitation; magnetospheric physics; FLUX-TRANSFER EVENTS; INTERPLANETARY MAGNETIC-FIELD; DAYSIDE AURORAL ACTIVITY; HF RADAR OBSERVATIONS; HIGH-LATITUDE CONVECTION; CUTLASS FINLAND RADAR; EISCAT SVALBARD RADAR; IONOSPHERIC CONVECTION; VELOCITY-MEASUREMENTS; PLASMA CONVECTION; Svalbard; Norway; Lockwood; Leicester; Cowley; EISCAT; Norwegian Polar Institute
• Online Access: http://www.ann-geophys.net/21/693/2003/; http://hdl.handle.net/2381/39329; https://doi.org/10.5194/angeo-21-693-2003

We present multi-instrument observations using the meridian scanning photometer (MSP) at Ny Alesund, the ˚ EISCAT Svalbard radar (ESR) and the CUTLASS Finland HF radar, to investigate the dynamics of the cusp region during pulsed reconnection events. The optical data obtained from the MSP indicate the presence of several polewardmoving auroral forms (PMAFs) which have been previously identified as the auroral signature of pulsed reconnection. Furthermore, the optical green line (557.7 nm) luminosity indicates a loss of emission equatorward of the location of the onset of the PMAFs, characteristic of magnetospheric plasma escaping to the magnetosheath along newly opened field lines. This reduction in green line luminosity creates a “dark region”, the equatorward edge of which is found to lie close to the boundary between high and low spectral widths observed by the CUTLASS Finland radar. High spectral widths on the dayside have previously been identified as a good indicator of cusp backscatter. Both of these boundaries have been suggested to provide an accurate representation of the location of the open/closed field line boundary. The ESR observations show enhancements in electron density and electron temperature occurring in conjunction with the optical PMAFs. The observations demonstrate some correspondence with the theoretical predictions of Davis and Lockwood (1996), who used an auroral precipitation model to predict ESR observations in the vicinity of the cusp. However, the limitations of this model are apparent under conditions of large plasma flows in the ionosphere. Finally, convection velocities obtained from the HF radar data illustrate a flow regime similar to that predicted to be driven by strong IMF By , as described by Cowley and Lockwood (1992), demonstrating an initial azimuthal flow followed by a rotation to more poleward directions. The CUTLASS HF radars were deployed and operated by the University of Leicester, and are supported by the UK Particle Physics and Astronomy Research Council (PPARC grant PPA/R/R/1997/00256), the Finnish Meteorological Institute, and the Swedish Institute of Space Physics. The authors would like to thank the Director of EISCAT and his staff for operating the facility and providing the EISCAT radar data. EISCAT is an international association supported by the research councils of Finland (SA), France (CNRS), Germany (MPG), Japan (NIPR), Norway (NAVF), Sweden (NFA), and the United Kingdom (PPARC). We also thank the principal investigators, N. Ness and D. L. McComas for supplying the ACE Science Center with high time resolution data from the ACE MAG and SWEPAM instruments, respectively. The auroral observation program on Svalbard is supported by the Norwegian Research Council and the Norwegian Polar Institute. Drs H. Khan, J .A. Davies and S. E. Milan are supported on PPARC grant PPA/G/O/1999/00181. Peer-reviewed Publisher Version