posted on 2017-01-24, 11:36authored byJ. K. Gauld, T. K. Yeoman, J. A. Davies, S. E. Milan, F. Honary
Coherent scatter HF ionospheric radar systems such as SuperDARN offer a powerful experimental technique for the investigation of the magnetospheric substorm. However, a common signature in the early expansion phase is a loss of HF backscatter, which has limited the utility of the radar systems in substorm research. Such data loss has generally been attributed to either HF absorption in the D-region ionosphere, or the consequence of regions of very low ionospheric electric field. Here observations from a well-instrumented isolated substorm which resulted in such a characteristic HF radar data loss are examined to explore the impact of the substorm expansion phase on the HF radar system. The radar response from the SuperDARN Hankasalmi system is interpreted in the context of data from the EIS-CAT incoherent scatter radar systems and the IRIS Riometer at Kilpisjarvi, along with calculations of HF absorption for both IRIS and Hankasalmi and ray-tracing simulations. Such a study offers an explanation of the physical mechanisms behind the HF radar data loss phenomenon. It is found that, at least for the case study presented, the major cause of data loss is not HF absorption, but changes in HF propagation conditions. These result in the loss of many propagation paths for radar backscatter, but also the creation of some new, viable propagation paths. The implications for the use of the characteristics of the data loss as a diagnostic of the substorm process, HF communications channels, and possible radar operational strategies which might mitigate the level of HF radar data loss, are discussed.
Funding
The CUTLASS HF radars are deployed and
operated by the University of Leicester, and are jointly funded by
the UK Particle Physics and Astronomy Research Council (Grant
no. PPA/R/R/1997/00256), the Finnish Meteorological Institute,
and the Swedish Institute for Space Physics. The authors thank
the director and staff of EISCAT for the operation of the facility
and dissemination of the data. EISCAT is an international facility
funded collaboratively by the research councils of Finland (SA),
France (CNRS), the Federal Republic of Germany (MPG), Japan
(NIPR), Norway (NAVF), Sweden (NFR) and the United Kingdom
(PPARC). IMAGE data were kindly supplied by the Finnish Meteorological
Institute. JKG was supported by a PPARC studentship.
JAD is supported on PPARC Grant number PPA/G/O/1997/000254.
The riometer data originated from the Imaging Riometer for Ionospheric
Studies (IRIS), operated by the Department of Communications
Systems at Lancaster University (UK), funded by the Particle
Physics and Astronomy Research Council (PPARC) in collaboration
with the Sodankyla Geophysical Observatory.
History
Citation
Annales Geophysicae, 2002, 20 (10), pp. 1631-1645 (15)
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
Version
VoR (Version of Record)
Published in
Annales Geophysicae
Publisher
European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)