A statistical study of large field-aligned flows of thermal ions at high-latitudes

Keating, John G.; Mulligan, F. J.; Doyle, D.B.; Winser, K.J.; Lockwood, Mike

doi:10.1016/0032-0633(90)90026-m

Cited by 34 publications

(59 citation statements)

References 28 publications

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“…Type 2 up¯ows occur above auroral arcs and are associated with increased electron temperature and ®eld-parallel electric ®elds. Keating et al (1990) presented a statistical study of large F-region ®eld-parallel¯ows. 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-aligned ows for a range of altitudes between 200 and 500 km.…”

Section: A1mentioning

confidence: 99%

“…However, the large data bases that are accumulated and the excellent temporal resolution achieved do allow for informative studies of ion up¯ow events, such as that presented by Keating et al (1990). Since that particular survey, EISCAT observations have been made over several more years, including topside measurements up to about 1000 km altitude.…”

Section: A1mentioning

confidence: 99%

“…The study is extended in altitude with measurements from Common Programme Seven obtained between 1990 and 1995. Diurnal and seasonal up¯ow distributions are ®rst presented and discussed brie¯y with regard to the ®ndings of Keating et al (1990). Then, the high-altitude CP-7 observations are considered, followed by an investigation of the occurrence frequency of IUEs as a function of the phase of the solar cycle.…”

Section: A1mentioning

confidence: 99%

“…Identical criteria to those adopted by Keating et al (1990) have been used in the present study to de®nè`e vents'' of ion up¯ow. Thus an up¯ow was de®ned as an upward ®eld-aligned¯ux of greater than 10 13 m A2 s…”

Section: Selection Criteria For Identi®cation Of Ion Up¯ow Eventsmentioning

confidence: 99%

“…The generally poorer signal quality received from the farther range gates therefore resulted in fewer observations at higher altitudes. This selection technique diers from that used by Keating et al (1990). These authors de®ned an observation simply as a single post-integration period, thus obtaining the same number of observations regardless of altitude.…”

Section: A1mentioning

confidence: 99%

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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

Foster

Lester²,

Davies³

1998

Ann. Geophys.

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Abstract. A statistical analysis of F-region and topside auroral ion up¯ow 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 up¯ow events (IUEs) is examined over the altitude range 200 to 500 km, using ®eld-aligned observations from CP-1 and CP-2. The study is extended in altitude with vertical measurements from CP-7. Ion up¯ow events were identi®ed by consideration of both velocity and¯ux, with threshold values of 100 m s A1 and 10 13 m A2 s A1, respectively. The frequency of occurrence of IUEs is seen to increase with increasing altitude. Further analysis of the ®eld-aligned observations reveals that the number and nature of ion up¯ow events vary diurnally and with season and solar activity. In particular, the diurnal distribution of up¯ows is strongly dependent on solar cycle. Furthermore, events identi®ed by the velocity selection criterion dominate at solar minimum, whilst events identi®ed by the upward ®eld-aligned¯ux criterion dominated at solar maximum. The study also provides a quantitative estimate of the proportion of up¯ows that are associated with enhanced plasma temperature. Between 50 and 60% of up¯ows are simultaneous with enhanced ion temperature, and approximately 80% of events are associated with either increased F-region ion or electron temperatures.

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Section: A1mentioning

confidence: 99%

Section: A1mentioning

confidence: 99%

Section: A1mentioning

confidence: 99%

Section: Selection Criteria For Identi®cation Of Ion Up¯ow Eventsmentioning

confidence: 99%

Section: A1mentioning

confidence: 99%

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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

Foster

Lester²,

Davies³

1998

Ann. Geophys.

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Ion upflow dependence on ionospheric density and solar photoionization

et al. 2015

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Motivated by rocket observations showing a variety of different ionospheric responses to precipitation, this paper explores the influence of the background ionospheric density on upflow resulting from auroral precipitation. Simulations of upflow driven by auroral precipitation were conducted using a version of the Varney et al. (2014) model driven by precipitation characterized by observations made during the 2012 Magnetosphere‐Ionosphere Coupling in the Alfvén resonator rocket mission and using a variety of different initial electron density profiles. The simulation results show that increased initial density before the onset of precipitation leads to smaller electron temperature increases, longer ionospheric heating timescales, weaker ambipolar electric fields, lower upflow speeds, and longer upflow timescales but larger upflow fluxes. The upflow flux can increase even when the ambipolar electric field strength decreases due to the larger number of ions that are accelerated. Long‐term observations from the European Incoherent Scatter (EISCAT) Svalbard radar taken during the International Polar Year support the effects seen in the simulations. This correlation between ionospheric density and ion upflows emphasizes the important role of photoionization from solar ultraviolet radiation, which the EISCAT observations show can increase ionospheric density by as much as an order of magnitude during the summer months.

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Average field‐aligned ion velocity over the EISCAT radars

2017

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Long‐term measurements by the European Incoherent Scatter (EISCAT) radars at Tromsø (69.6°N, 19.2°E) and Svalbard (78.2°N, 16.0°E) are used to determine the climatology of the field‐aligned ion velocity in the F region ionosphere (175–475 km) at high latitudes. The average ion velocity is calculated at various altitudes and times of day. The magnitude of the average field‐aligned ion velocity is on the order of 10 m/s, similar to previous results at middle and low latitudes. The results obtained for the two radars are in good agreement. During daytime the direction of the average field‐aligned ion velocity changes from downward to upward around 350 km, while during nighttime it is upward at all heights. The reversal height of the daytime field‐aligned ion velocity depends on solar activity. It is elevated by more than 100 km during high solar flux periods compared to low solar flux periods. The Thermosphere Ionosphere Electrodynamics General Circulation Model reproduces the main features of the field‐aligned ion velocity climatology. The simulation results suggest that the plasma pressure gradient force and gravity force play a dominant role for the daytime field‐aligned ion motion. The height pattern of the field‐aligned ion velocity tends to be preserved in different solar activity conditions at constant pressure surfaces, but not at constant altitudes, which explains the observed dependence on solar activity. During nighttime, the effect of the neutral wind dominates the field‐aligned ion velocity.

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A statistical study of large field-aligned flows of thermal ions at high-latitudes

Cited by 34 publications

References 28 publications

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

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

Ion upflow dependence on ionospheric density and solar photoionization

Average field‐aligned ion velocity over the EISCAT radars

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