Interhemispheric comparison of spectral width boundary as observed by SuperDARN radars
Previous studies have shown that dayside equatorward edge of coherent HF radar backscatter having broad Doppler spectral width is coincident with the equatorward edge of the cusp particle precipitation. This enables the boundary between broad and narrow spectral width backscatters (spectral width bo...
| 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/21/1553/2003/angeo-21-1553-2003.html http://hdl.handle.net/2381/39438 https://doi.org/10.5194/angeo-21-1553-2003 |
| Summary: | Previous studies have shown that dayside equatorward edge of coherent HF radar backscatter having broad Doppler spectral width is coincident with the equatorward edge of the cusp particle precipitation. This enables the boundary between broad and narrow spectral width backscatters (spectral width boundary) in the dayside magnetic local time sector to be used as a proxy for the open/closed field line boundary. The present case study employs magnetically conjugate SuperDARN coherent HF radars to make an inter-hemispheric comparison of the location and variation of the spectral width boundaries. Agreement between the magnetic latitudes of the boundaries in both hemispheres is remarkable. Correlation coefficients between the latitudes of the boundaries are larger than 0.70. Temporal variation of the spectral width boundary follows the same equatorward trend in both hemispheres. This is consistent with the accumulation of open flux in the polar cap by dayside low-latitude magnetopause reconnection, expected when IMF Bz is negative. Boundaries in both hemispheres also exhibit short-lived poleward motions superposed on the general equator-ward trend, which follows the onset of substorm expansion phase and a temporary northward excursion of IMF Bz during substorm recovery phase. There is an interhemispheric difference in response time to the substorm occurrence between two hemispheres. The spectral width boundary in the Southern Hemisphere starts to move poleward 10 min earlier than that in the Northern Hemisphere. We discuss this difference in terms of interhemispheric asymmetry of the substorm breakup region in the longitudinal direction associated with the effect of IMF By. The Ministry of Education, Culture, Sports, Science and Technology supports the SENSU Syowa HF radar systems. The 39th and 40th JAREs (Japanese Antarctic Research Expedition) have carried out the HF radar operation at Syowa station. The Iceland East-Finland radar pair (the Co-operative UK Twin Located Auroral Sounding System: CUTLASS) is funded by the Particle Physics and Astronomy Research Council, U.K., under grant PPA/R/R/1997/00256, the Finnish Meteorological Institute, Helsinki, and the Swedish Institute for Space Research, Uppsala. The authors would like to thank N. Ness at Bartol Research Institute and CDAWeb for access to key parameter data from the MFI instrument onboard the ACE spacecraft. The authors also thank the principle investigator, R. P. Lepping, for the use of key parameters from the Wind MFI instruments. The CANOPUS instrument array is constructed, maintained and operated by the Canadian Space Agency. D. Hardy of Phillips Laboratory designed and built the DMSP SSJ/4 particle detectors employed in this study. This research is supported by the Grant-in Aid for Scientific Research (A:11304029) from Japan Society for the Promotion of Science (JSPS). KH is supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. EEW is indebted to the Particle Physics and Astronomy Research Council (PPARC) for a research studentship. Peer-reviewed Publisher Version |
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