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A statistical study of diurnal, seasonal and solar cycle variations of F-region and topside auroral upflows observed by EISCAT between 1984 and 1996

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journal contribution
posted on 18.03.2015, 11:26 by C. Foster, Mark Lester, J. A. Davies
A statistical analysis of F-region and topside auroral ion upflow events is presented. The study is based on observations from EISCAT Common Programmes (CP) 1 and 2 made between 1984 and 1996, and Common Programme 7 observations taken between 1990 and 1995. The occurrence frequency of ion upflow events (IUEs) is examined over the altitude range 200 to 500 km, using field-aligned observations from CP-1 and CP-2. The study is extended in altitude with vertical measurements from CP-7. Ion upflow events were identified by consideration of both velocity and flux, with threshold values of 100 m s–1 and 1013 m–2 s–1, respectively. The frequency of occurrence of IUEs is seen to increase with increasing altitude. Further analysis of the field-aligned observations reveals that the number and nature of ion upflow events vary diurnally and with season and solar activity. In particular, the diurnal distribution of upflows is strongly dependent on solar cycle. Furthermore, events identified by the velocity selection criterion dominate at solar minimum, whilst events identified by the upward field-aligned flux criterion dominated at solar maximum. The study also provides a quantitative estimate of the proportion of upflows that are associated with enhanced plasma temperature. Between 50 and 60% of upflows are simultaneous with enhanced ion temperature, and approximately 80% of events are associated with either increased F-region ion or electron temperatures.

Funding

C. Foster was supported by a studentship from the Particle Physics and Astronomy Research Council of the United Kingdom.

History

Citation

ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES, 1998, 16 (10), pp. 1144-1158 (15)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Source

8th EISCAT Scientific Workshop, UNIV LEICESTER, LEICESTER, ENGLAND

Version

VoR (Version of Record)

Published in

ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES

Publisher

European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)

issn

0992-7689

eissn

1432-0576

Copyright date

1998

Available date

18/03/2015

Publisher version

http://www.ann-geophys.net/16/1144/1998/angeo-16-1144-1998.html

Temporal coverage: start date

23/06/1997

Temporal coverage: end date

27/06/1997

Language

en