Ion upflow and downflow at the topside ionosphere observed by the EISCAT VHF radar

Endo, Mitsuru; Fujii, Ryoichi; Ogawa, Y.; Buchert, Stephan; Nozawa, Satonori; Watanabe, Shigeto; Yoshida, Nao

doi:10.1007/s00585-000-0170-3

Cited by 26 publications

(35 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…For identifying occurrence of ionospheric ion upflow, several criteria for selecting ion upflow events have previously been adopted [e.g., Endo et al , 2000; Buchert et al , 2004; Ogawa et al , 2009]. In the topside ionosphere, the signal‐to‐noise ratio becomes low, and sometimes the fits of incoherent scatter (IS) spectra converged to unrealistically high velocities.…”

Section: Instruments and Datamentioning

confidence: 99%

Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromsø UHF radar

et al. 2010

Self Cite

View full text Add to dashboard Cite

The influence of solar activity upon ion upflow in the polar ionosphere was investigated using data obtained by the European Incoherent Scatter (EISCAT) Tromsø UHF radar between 1984 and 2008. In agreement with other work we find that the upward ion flux is generally higher when solar activity is high than when it is low. Ion upflow events and also the upward velocity behave the opposite: they are more frequently seen and higher, respectively, at times of low solar activity. In any year about 30–40% ion upflow is accompanied by ∼500 K higher electron temperature than the background temperature at 400 km altitude. Electron and ion heating in connection with upflow is nearly twice as prevalent during high solar activity as it is at low activity. The acceleration of ions by pressure gradients and ambipolar electric field becomes larger when solar activity is low than when it is high. This variation of the average acceleration is caused by the different shapes of electron density profiles for low and high solar activities. Ions start to flow up at above 450 km altitude when solar activity was high, and lower, at 300–500 km altitude, at low solar activity. It is suggested that the solar activity influences long‐term variations of the ion upflow occurrence because it modulates the density of neutral particles, the formation of the F2 density peak, and ion‐neutral collision frequencies in the thermosphere and ionosphere.

show abstract

Section: Instruments and Datamentioning

confidence: 99%

Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromsø UHF radar

et al. 2010

Self Cite

View full text Add to dashboard Cite

show abstract

“…7. Similar criteria were used and are discussed in Endo et al (2000) for a statistical study of VHF data, where, however, simultaneous up-and down-(i.e. diverging field-aligned) flow was not searched for in that study.…”

Section: Statistical Occurrencementioning

confidence: 99%

“…Also, ion downflow events are seen at any time and at the geomagnetic disturbance level in EISCAT VHF data (Endo et al, 2000). This downflow is usually isolated from upflow events.…”

Section: Introductionmentioning

confidence: 99%

Observations of diverging field-aligned ion flow with the ESR

Buchert

Ogawa²,

Fujii³

et al. 2004

Ann. Geophys.

Self Cite

View full text Add to dashboard Cite

Abstract. We report on observations of a diverging ion flow along the geomagnetic field that is often seen at the EISCAT Svalbard radar. The flow is upward above the peak of the electron density in the F-region and downward below the peak. We estimate that in such events mass transport along the field line is important for the ionization balance, and that the shape of the F-layer and its ion composition should be strongly influenced by it. Diverging flow typically occurs when there are signatures of direct entry of sheath plasma to the ionosphere in the form of intense soft particle precipitation, and we suggest that it is caused by the ionization and ionospheric electron heating associated with this precipitation. On average, 30% of all events with ion upflow also show significant ion downflow below.

show abstract

“…Statistical and case studies of the ion upflow have been made with the European Incoherent Scatter (EISCAT) Kiruna‐Sodankylä‐Tromsø (KST) radar facility located near Tormsø [ Blelly et al , 1992; Wahlund et al , 1992; Keating et al , 1990; Foster et al , 1998; Endo et al , 2000]. The EISCAT KST radar enables us to investigate the characteristics of ion upflow, in particular, in the closed field line region because of its location of the invariant latitude of 66.2°.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous EISCAT Svalbard radar and DMSP observations of ion upflow in the dayside polar ionosphere

et al. 2003

Self Cite

View full text Add to dashboard Cite

[1] Regions where dayside field-aligned (FA) ion upflows occur are identified, and the relative occurrences and characteristics are compared. The study is based on $170 simultaneous events observed with the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and spacecraft from the DMSP. We found that ion upflows occur not only in the cusp and cleft (the low-altitude portion of the low-latitude boundary layer), which traditionally have been regarded as regions of ion upflow, but also in the region connected to the mantle. Ion upflows are less frequently seen in the boundary plasma sheet (BPS) and are very rarely seen in the central plasma sheet at high latitude on the dayside. Almost all of the events in which the average FA ion velocity is >100 m s À1 are associated with relatively high soft electron precipitation (differential energy flux of electrons at 100 eV > 10 7 eV cm À2 s À1 sr À1 eV À1), although soft electron precipitation with similarly high flux exists also in the BPS, where the ion velocities are mostly <100 m s À1 . These results indicate that soft particle precipitation is the predominant energy source driving ion upflow in the topside ionosphere, but it triggers ion upflow effectively not in the BPS, only in the other high-latitude regions on the dayside.

show abstract

Ion upflow and downflow at the topside ionosphere observed by the EISCAT VHF radar

Cited by 26 publications

References 49 publications

Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromsø UHF radar

Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromsø UHF radar

Observations of diverging field-aligned ion flow with the ESR

Simultaneous EISCAT Svalbard radar and DMSP observations of ion upflow in the dayside polar ionosphere

Contact Info

Product

Resources

About