Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> 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<sup>â1</sup> and 10<sup>13</sup> m<sup>â2</sup> s<sup>â1</sup>, 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.<br><br><b>Key words.</b> Ionosphere (auroral ionosphere; particle acceleration)
Highlights
Over the last two decades, a wealth of radar and satellite observations has revealed that the ionosphere provides a steady and signi®cant source of magnetospheric ions
This paper presents a statistical study of F-region and topside ion upow events observed by the EISCAT radar between 1984 and 1996
The initial study examined 12 y of EISCAT ®eld-aligned measurements derived from Common Programmes One and Two
Summary
Over the last two decades, a wealth of radar and satellite observations has revealed that the ionosphere provides a steady and signi®cant source of magnetospheric ions. Keating et al (1990) presented a statistical study of large F-region ®eld-parallelows These authors analysed EISCAT Common Programme 1 data collected between 1985 and 1987 and derived seasonal and diurnal distributions of the occurrence of large ®eld-alignedows for a range of altitudes between 200 and 500 km. This paper presents a statistical study of F-region and topside ion upow events observed by the EISCAT radar between 1984 and 1996. The occurrence frequency of ion upow events (IUEs) is studied over the altitude range 200 to 500 km, employing ®eld-aligned observations from Common Programmes One and Two. The study is extended in altitude with measurements from Common Programme Seven obtained between 1990 and 1995. A quantitative study of the relationship between IUEs and enhanced ion and electron temperatures is presented
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