Observations of diverging field-aligned ion flow with the ESR

Buchert, Stephan; Ogawa, Y.; Fujii, Ryoichi; Eyken, A. P. van

doi:10.5194/angeo-22-889-2004

Cited by 18 publications

(23 citation statements)

References 23 publications

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“…The resulting vertical pressure gradients would generate ion diffusion upward above the heating layer and downward below it. Statistical observations from the EISCAT Svalbard Radar lend some support to this interpretation (Buchert et al, ). However, ion downflow velocities due to pressure gradients are usually small (<1 km/s) (Buchert et al, ; Endo et al, ) compared to over 2–3 km/s in our study.…”

Section: Discussionmentioning

confidence: 92%

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

et al. 2018

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Heavy (O+) ion energization and field‐aligned motion in and near the ionosphere are still not well understood. Based on observations from the CAScade, Smallsat and IOnospheric Polar Explorer (CASSIOPE) Enhanced Polar Outflow Probe at altitudes between 325 km and 730 km over 1 year, we present a statistical study (24 events) of ion heating and its relation to field‐aligned ion bulk flow velocity, low‐frequency waves, and field‐aligned currents. The ion temperature and field‐aligned bulk flow velocity are derived from 2‐D ion velocity distribution functions measured by the suprathermal electron imager (SEI) instrument. Consistent ion heating and flow velocity characteristics are observed from both the SEI and the rapid‐scanning ion mass spectrometer instruments. We find that transverse O+ ion heating in the ionosphere can be intense (up to 4.5 eV), confined to very narrow regions (∼2 km across B), is more likely to occur in the downward current region and is associated with broadband extremely low frequency (BBELF) waves. These waves are interpreted as linearly polarized perpendicular to the magnetic field. The amount of ion heating cannot be explained by frictional heating, and the correlation of ion heating with BBELF waves suggests that significant wave‐ion heating is occurring and even dominating at altitudes as low as 350 km, a boundary that is lower than previously reported. Surprisingly, the majority of these heating events (17 out 24) are associated with core ion downflows rather than upflows. This may be explained by a downward pointing electric field in the low‐altitude return current region.

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Section: Discussionmentioning

confidence: 92%

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

et al. 2018

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“…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

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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.

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“…In general, it is useful to separate the problem into successive steps. The first step is the initial acceleration of bulk ion upflow events driven by ion heating and ambipolar diffusion as observed by incoherent scatter radars (ISRs) [ Wahlund et al ., ; Ogawa et al ., , , ; Buchert et al ., ; Skjæveland et al ., ], sounding rockets [ Arnoldy et al ., ; Lynch et al ., ; Frederick‐Frost et al ., ], and satellites in polar low Earth orbit in the F region ionosphere [ Coley et al ., ; Ogawa et al ., ; Lühr et al ., ; Chaston et al ., ; Lorentzen et al ., ; Sadler et al ., ]. The second step is that upflow events that have reached sufficiently high altitudes are exposed to wave energies available in the topside ionosphere/magnetosphere which drive nonthermal transverse acceleration of oxygen [ André and Yau , ; Strangeway et al ., ; Chaston et al ., ; Jacobsen and Moen , ].…”

Section: Introductionmentioning

confidence: 99%

“…Statistical work by Buchert et al . [] and Ogawa et al . [] showed that ion upflows above the European Incoherent Scatter Svalbard Radar (ESR) occurred for any magnetic local time (MLT) and Kp , but were most common around magnetic noon, with the peak at 13 MLT (upflow occurrence rate 18%) and somewhat more upflows prenoon (8–10%) than postnoon (5–10%, with a clear minimum around 18–20 MLT).…”

Section: Introductionmentioning

confidence: 99%

Which cusp upflow events can possibly turn into outflows?

2014

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Two sequences, before and after magnetic noon, respectively, of poleward moving auroral forms with associated upflows situated above the European Incoherent Scatter Svalbard Radar allowed close study of ion upflow dynamics. We find that flux intensity is correlated with plasma temperature and that upflowing plasma undergoes acceleration proportional to the slope of the velocity profile and to the velocity at each altitude. The potential for upflows to lift thermal plasma to regions where broadband extremely low frequency electric field activity can cause nonthermal acceleration leading to outflow is examined. Equations for estimating the travel time of upflowing plasma are presented. We find that around 40% of the observed upflow profiles with a unit number flux greater than 1 × 10 13 m À2 s À1 can transport plasma from 500 to 800 km altitude in less than 10 min, approximately the typical lifetime of pulsed upflow events. Almost all such profiles can transport plasma from 600 to 800 km in the same time span. Typical transport times for other altitude ranges are also presented. Post magnetic noon the background electron density was somewhat higher than prenoon due to transport of EUV-enhanced plasma, and the postnoon ion flux was somewhat weaker than prenoon.

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Observations of diverging field-aligned ion flow with the ESR

Cited by 18 publications

References 23 publications

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

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

Which cusp upflow events can possibly turn into outflows?

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