Incoherent scatter radar observations of the cusp acceleration region and cusp field‐aligned currents

Nilsson, Hans; Kirkwood, S.; Moretto, T.

doi:10.1029/98ja02269

Cited by 12 publications

(16 citation statements)

References 31 publications

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“…In the latter paper the upflow region observed by the EISCAT Svalbard incoherent scatter radar was connected to a dayside magnetospheric source region identified using DMSP satellite data. They found that the upflow occur both in the cusp (as reported by Nilsson et al, 1998) but also in the mantle region, just poleward of the cusp. Mid altitude satellite measurements have traced the source of mid altitude oxygen ion beams to the cusp region (Øieroset et al, 1999;Bouhram et al, 2004;Dubouloz et al, 1998), and also high altitude polar cap oxygen beams have been traced to the cusp region (Nilsson et al, 2004).…”

Section: Introductionmentioning

confidence: 95%

“…The ionospheric upflow there is strong due to both soft particle precipitation which strongly enhances the F-region electron temperature (Nilsson et al, 1994(Nilsson et al, , 1998Ogawa et al, 2003) and due to strong magnetospheric electric fields (Schunk et al, 1975). Mid altitude (3-5 R E ) satellites have identified the same region as the source of the cleft ion fountain (Lockwood et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

“…Ionospheric upflow in the cusp/cleft region has been studied by incoherent scatter radars, both Søndre Strømfjord (e.g Nilsson et al, 1998) and EISCAT Svalbard Radar (e.g. Ogawa et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Transients in oxygen outflow above the polar cap as observed by the Cluster spacecraft

et al. 2008

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Abstract. Oxygen ion outflow associated with the cusp and cleft give rise to persistent oxygen ion beams which can be observed over the polar cap. For high altitude spacecraft such as Cluster these beams are often observed for several hours on each occasion. This allows for a study of typical temporal structures on the time scale of minutes. We have used 3 years of data from spring, January to May of years 2001 to 2003, for a study of the oxygen number flux variation in the polar cap ion outflow. The source of these oxygen ion beams is the cusp and cleft, and variations in ionospheric upflow on time scales of around 8 min have been reported from ground based studies using incoherent scatter radar. Such upflows typically do not reach escape velocity, and further energization above the ionosphere is required for outflow to occur. Our study shows that a typical time scale between sudden number flux enhancements observed by Cluster in a geocentric distance range of 5 R E to 12 R E is 5 to 10 min. A superposed epoch study does not reveal any significant convection velocity or temperature changes around the flux enhancement events. Sudden temperature enhancements occur with a typical time interval of about 4 min, A superposed epoch study does not reveal any number flux enhancements associated with the temperature enhancements. The clear modulation of the high altitude number flux in a manner which resembles the modulation of the ionospheric upflow indicates that this is the main limiting factor determining the total outflow.Correspondence to: H. Nilsson (hans.nilsson@irf.se)The process behind transient upflow events in the ionosphere is therefore important for the total ionospheric outflow. Subsequent heating above the ionosphere appears to be common enough in the cusp/cleft region that it does not significantly modulate the oxygen ion number flux.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Transients in oxygen outflow above the polar cap as observed by the Cluster spacecraft

et al. 2008

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“…Ionospheric plasma may flow up from the ionosphere but at velocities which are low enough that the ions are still gravitationally bound (Nilsson et al, 1996). The initial upflow is caused by Joule heating of the ionospheric ions due to magnetospheric electric fields (Schunk et al, 1975), plasma heating due to particle precipitation and in particular ambipolar diffusion caused by effective heating of F-region electrons due to soft electron (100 eV) precipitation typical of the cusp (Moore et al, 1999;Nilsson et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Oxygen ion energization observed at high altitudes

et al. 2010

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Abstract. We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 R E ) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2-0.4 R E in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization.

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“…The cavity forms where ionospheric electrons move upward as the charge carriers for a downward FAC. The mechanism has been used by Nilsson et al (1998) to explain electron density cavities observed by incoherent scatter radar in the E and lower F-regions and to discuss the possible occurrence of localised density holes that may develop in regions of black aurorae (Marklund, 1997). The colocated narrow band of increased ion temperatures, extending upwards at about 77.5 • N (Fig.…”

Section: Simultaneous Lobe and Equatorial Reconnectionmentioning

confidence: 99%

EISCAT Svalbard radar observations of ionospheric signatures of magnetopause reconnection during a changing IMF Bz polarity

Pryse

Smith²,

Kersley³

et al. 2002

Ann. Geophys.

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Abstract.Observations by the EISCAT Svalbard radar are presented that show the response of the spatial structure of the ionosphere in the dayside cusp region to a rotational trend in the IMF clock angle. Over a period of one hour, the clock angle increased from about 45 • to some 150 • , moving the likely location of the magnetopause reconnection site from the high-latitude lobe to near the equatorial plane. Increased topside electron temperatures measured by the ESR identified footprints of the reconnection process. Temporal changes in the spatial distribution of the temperature reflected the change from lobe to equatorial reconnection. Discrete spatial enhancements in ion temperature were found resulting from ion-neutral frictional heating in the fast flows where it was likely that field lines were being convected from the reconnection locations. The corresponding electron density structuring is interpreted in terms of the particle precipitation, field-aligned currents and convection flows driven by the IMF.

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Incoherent scatter radar observations of the cusp acceleration region and cusp field‐aligned currents

Cited by 12 publications

References 31 publications

Transients in oxygen outflow above the polar cap as observed by the Cluster spacecraft

Transients in oxygen outflow above the polar cap as observed by the Cluster spacecraft

Oxygen ion energization observed at high altitudes

EISCAT Svalbard radar observations of ionospheric signatures of magnetopause reconnection during a changing IMF Bz polarity

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