Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Hubert, Benoît; Aikio, Anita; Amm, O.; Pitkänen, Timo; Kauristie, Kirsti; Milan, S. E.; Cowley, S. W. H.; Gérard, Jean‐Claude

doi:10.5194/angeo-28-883-2010

Cited by 22 publications

(30 citation statements)

References 31 publications

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“…∼ 0.5 • MLAT on average (this number was found to depend on substorm phase; we refer the interested reader to the original study). Hubert et al (2010) also show an interval for which the discrepancy can reach ∼ 1.9 • MLAT on average, which remains relatively good considering that the space resolution of the SI12 instrument is on the order of 1 • MLAT. These authors also undertook a comparison with the location of the magnetic convection reversal boundary (MCRB) and with the boundary location found from observation of the OI( 1 D) emission at 630 nm.…”

Section: Introductionsupporting

confidence: 53%

“…They also showed that magnetic flux is closed by pseudo-breakups and that poleward boundary intensifications (PBIs) observed during the recovery phase result from minor reactivations of flux closure in the tail. In addition to the DMSP validation done by Hubert et al (2006a), Hubert et al (2010) compared the global-scale boundary determination from the IMAGE-FUV (Far Ultraviolet)-SI12 observations with the polar cap boundary location determined locally at a higher space and time resolution using the European Incoherent Scatter Scientific Association (EISCAT) facility. Both methods showed an acceptable agreement: for most of the analysed intervals, the polar cap boundary determined by both methods is collocated within the space resolution of both methods, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

Hubert¹,

Gérard²,

Milan

et al. 2017

Ann. Geophys.

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Abstract. We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average ∼ 0.745 GWb, standard deviation ∼ 0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of ∼ 450 km s −1 . We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals.

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Section: Introductionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

Hubert¹,

Gérard²,

Milan

et al. 2017

Ann. Geophys.

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“…The PCB is identified from the EISCAT incoherent scatter radar data by utilising the method described in Aikio et al (2006) and applied in several studies together with satellite and MIR-ACLE magnetometer data (e.g. Aikio et al, 2008;Pitkänen et al, 2009aPitkänen et al, , b, 2011Hubert et al, 2010). Global simulation is provided by GUMICS-4, which solves the ideal MHD equations in the solar wind and in the magnetosphere, and is coupled to the electrostatic ionosphere.…”

Section: Introductionmentioning

confidence: 99%

IMF effect on the polar cap contraction and expansion during a period of substorms

et al. 2013

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The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase.

In addition, we suggest that the IMF B_z component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further

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“…5 as a gradual shift of the electrojet to lower latitudes. As demonstrated, for example, by Hubert et al (2010) the poleward boundary of morning-sector westward equivalent currents can sometimes be used as a proxy for the open-closed field-line boundary (polar cap boundary). Estimating the polar cap location and its motion is not straightforward in our first event (Fig.…”

Section: Results From the Secs Analysismentioning

confidence: 99%

“…In the approach developed by Amm (1997) and Amm and Viljanen (1999) the two components of ionospheric currents are represented with two different types of SECSs. For mathematical and graphical representation of these systems, see, e.g., Juusola et al (2006). For creating two-dimensional (2-D) equivalent current patterns for the Fennoscandian region we use a grid of divergence-free elementary current systems, where the poles of the systems cover the latitude-longitude region from 53.9 • N, 2.5 • E (south-west edge) to 83.9 • N, 43.1 • E (north-east edge).…”

Section: Deriving Ionospheric Equivalent Currents From Ground-based Mmentioning

confidence: 99%

Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms

et al. 2016

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Abstract. Space and time variations of equivalent currents during morning-sector Pc5 pulsations (T ∼ 2-8 min) on 2 days (18 January and 19 February 2008) are studied in the context of substorm activity with THEMIS and MIRACLE ground-based instruments and THEMIS P3, P5, and P2 probes. These instruments covered the 22:00-07:00 magnetic local time during the analyzed events. In these cases abrupt changes in the Pc5 amplitudes, intensifications and/or weakenings, were recorded some minutes after auroral breakups in the midnight sector. We analyze three examples of Pc5 changes with the goal to resolve whether substorm activity can have an effect on Pc5 amplitude or not. In two cases (on 19 February) the most likely explanation for Pc5 amplitude changes comes from the solar wind (changes in the sign of interplanetary magnetic field B z ). In the third case (on 18 January) equivalent current patterns in the morning sector show an antisunward-propagating vortex which replaced the Pc5-related smaller vortices and consequently the pulsations weakened. We associate the large vortex with a field-aligned current system due to a sudden, although small, drop in solar wind pressure (from 1 to 0.2 nPa). However, the potential impact of midnight substorm activity cannot be totally excluded in this case, because enhanced fluxes of electrons with high enough energies (∼ 280 keV) to reach the region of Pc5 within the observed delay were observed by THEMIS P2 at longitudes between the midnight and morning-sector instrumentation.

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Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Cited by 22 publications

References 31 publications

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

IMF effect on the polar cap contraction and expansion during a period of substorms

Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms

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