The magnetospheric driver of subauroral ion drifts

Keyser, Johan De; Roth, M.; Lemaire, J.

doi:10.1029/98gl01135

Cited by 46 publications

(48 citation statements)

References 15 publications

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“…According to their model, SAID events would occur predominantly in the premidnight sector, where the inner edge of the proton ring current extends earthward of the inner edge of the electron ring current. The production mechanism proposed later on by Keyser et al (1998) also predicted the same result. Due to the relative motion between the hot injected plasma and the plasmaspheric corotation shear velocity at the cold plasma trough interface, which is largest in the premidnight sector, SAID would predominantly occur in this region.…”

Section: Discussionsupporting

confidence: 73%

“…Some authors have focused on the corresponding intense poleward-directed electric fields, reporting events with intensities greater than approximately 30 mV/m (Smiddy et al, 1977;Maynard, 1978;Maynard et al, 1980;Rich et al, 1980;Karlsson et al, 1998). SAID structures are confined to latitudinally narrow regions (0.1 • -2 • CGLatCorrected Geomagnetic Latitude), equatorwards of the auroral zone (Karlsson et al, 1998;Galperin et al, 1997;Anderson et al, 2001), occur predominantly in the premidnight MLT (Magnetic Local Time) sector (18:00-02:00 MLT, S. Figueiredo et al: Investigation of subauroral ion drifts according to Spiro et al (1979), Karlsson et al (1998) and Anderson et al (2001)) and are substorm related (Smiddy et al, 1977;Maynard, 1978;Spiro et al, 1979;Maynard et al, 1980;Rich et al, 1980;Anderson et al, 1993;Karlsson et al, 1998;Keyser et al, 1998;Keyser, 1999;Burke et al, 2000;Anderson et al, 2001;Galperin, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…These results are in agreement with the model proposed by Anderson et al (1993) and clearly indicate that the SAID phenomenon has a close relationship to the mid-latitude trough and the currents flowing through this region. Keyser et al (1998) and Keyser (1999) presented a different mechanism for the formation and evolution of SAID in the course of a substorm. In this model, SAID is considered as the ionospheric signature of a voltage difference generated across a magnetospheric current sheet, interfacing the cold plasma trough and hot injected plasma moving inward.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

2004

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Abstract. Based on Astrid-2 satellite data, results are presented from a statistical study on subauroral ion drift (SAID) occurrence. SAID is a subauroral phenomenon characterized by a westward ionospheric ion drift with velocity greater than 1000 m/s, or equivalently, by a poleward-directed electric field with intensity greater than 30 mV/m. SAID events occur predominantly in the premidnight sector, with a maximum probability located within the 20:00 to 23:00 MLT sector, where the most rapid SAID events are also found. They are substorm related, and show first an increase in intensity and a decrease in latitudinal width during the expansion phase, followed by a weakening and widening of the SAID structures during the recovery phase. The potential drop across a SAID structure is seen to remain roughly constant during the recovery phase.The field-aligned current density and the height-integrated Pedersen conductivity distribution associated with the SAID events were calculated. The results reveal that the strongest SAID electric field peaks are associated with the lowest Pedersen conductivity minimum values. Clear modifications are seen in the ionospheric Pedersen conductivity distribution associated with the SAID structure as time evolves: the SAID peak is located on the poleward side of the corresponding region of reduced Pedersen conductivity; the shape of the regions of reduced conductivity is asymmetric, with a steeper poleward edge and a more rounded equatorward edge; the SAID structure becomes less intense and widens with evolution of the substorm recovery phase. From the analysis of the SAID occurrence relative to the mid-latitude trough position, SAID peaks are seen to occur relatively close to the corresponding mid-latitude trough minimum. Both these features show a similar response to magnetospheric disturbances, but on different time scales -with increasing magnetic activity, the SAID structure shows a faster movement towards lower latitudes than that of the mid-latitude trough.From the combined analysis of these results, we conclude that the SAID generation mechanism cannot be regarded ei- ther as a pure voltage generator or as a pure current generator, applied to the ionosphere. While the anti-correlation between the width and the peak intensity of the SAID structures with substorm evolution indicates a magnetospheric source acting as a constant voltage generator, the ionospheric modifications and, in particular the reduction in the conductivity for intense SAID structures, are indicative of a constant current system closing through the ionosphere. The ionospheric feedback mechanisms are seen to be of major importance for sustaining and regulating the SAID structures.

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Section: Discussionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

2004

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“…Magnetospheric flow shears are expected, for instance, on closed field lines near the plasmasphere and near the edges of plasmaspheric plumes, especially when hot plasmasheet plasma is injected in the inner magnetosphere during a substorm (McIlwain, 1974;Newell and Meng, 1987;Baker and McPherron, 1990), and in the low latitude boundary layer where the antisunward flow of magnetosheath plasma interfaces with the magnetospheric plasma (Lundin and Evans, 1985;Feldstein et al, 2001;Echim et al, 2008), but also in the plasmasheet (Galperin and Feldshtein, 1989;Baumjohann et al, 1990;Angelopoulos et al, 1992;Chen et al, 2000;Figueiredo et al, 2005;Hamrin et al, 2006;Marghitu et al, 2006;Liléo et al, 2008;Johansson et al, 2009). A second type of electric fields are charge separation electric fields, possibly strengthened by the presence of shear flows, especially at interfaces between cold (plasmasphere/plasmatrough or lobe) and hot (plasmasheet) plasmas, as invoked for discrete arc and subauroral ion drift generators (Ejiri et al, 1980;Feldstein and Galperin, 1985;Yeh et al, 1991;Roth et al, 1993;Lemaire et al, 1998;De Keyser et al, 1998;De Keyser, 1999Johansson et al, 2006;Echim et al, 2007); such fields are capable of creating fine scale structure. Charge separation fields are typically produced at an interface between plasmas with different temperatures or composition: Because their gyroradii are different, exact charge neutrality is impossible to achieve in the interface (Roth et al, 1996).…”

Section: Discussionmentioning

confidence: 99%

“…The generator must be able to sustain the magnetospheric electric fields on a time scale that is long enough to set up the ionospheric configuration. It has been argued that, for instance, discrete arcs and subauroral ion drift layers are indeed powered by such magnetospheric generators (e.g., Roth et al, 1993;De Keyser et al, 1998;Echim et al, 2007Echim et al, , 2009. Although one cannot exclude the possibility of an ionospheric generator, as might be the case for polar cap arcs and theta aurorae (Zhu et al, 1993(Zhu et al, , 2005, that situation is not considered here.…”

Section: Introductionmentioning

confidence: 96%

Auroral and sub-auroral phenomena: an electrostatic picture

Keyser

Echim

2010

Ann. Geophys.

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Abstract. Many auroral and sub-auroral phenomena are manifestations of an underlying magnetosphere-ionosphere coupling. In the electrostatic perspective the associated auroral current circuit describes how the generator (often in the magnetosphere) is connected to the load (often in the ionosphere) through field-aligned currents. The present paper examines the generic properties of the current continuity equation that characterizes the auroral circuit. The physical role of the various elements of the current circuit is illustrated by considering a number of magnetospheric configurations, various auroral current-voltage relations, and different types of behaviour of the ionospheric conductivity. Based on realistic assumptions concerning the current-voltage relation and the ionospheric conductivity, a comprehensive picture of auroral and sub-auroral phenomena is presented, including diffuse aurora, discrete auroral arcs, black aurora, and subauroral ion drift. The electrostatic picture of field-aligned potential differences, field-aligned currents, ionospheric electric fields and plasma drift, and spatial scales for all these phenomena is in qualitative agreement with observations.

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Solar cycle, seasonal, and diurnal variations of subauroral ion drifts: Statistical results

2014

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The solar cycle, seasonal, and diurnal variations of the subauroral ion drifts (SAIDs) are investigated for the first time to use such a large database of 18,226 SAID events observed by the DMSP satellites during 1987-2012. Statistical results show that SAIDs occur mostly at 60.1°invariant latitude and 2230 magnetic local time with a typical half width of 0.57°, move equatorward during high solar activities with large widths, and have two occurrence peaks in spring and fall equinoxes and two valleys in summer and winter solstices. The seasonal variation of SAID latitude has two valleys in spring and fall, and SAID width has a valley distribution with a minimum in summer. SAIDs exhibit a clear day-to-night difference in latitude. The diurnal variation of SAID width has a morning valley and an afternoon peak. The generation mechanism of SAID associated with the electron precipitation and the downward field-aligned current is also supported in this study.

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The magnetospheric driver of subauroral ion drifts

Cited by 46 publications

References 15 publications

Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

Auroral and sub-auroral phenomena: an electrostatic picture

Solar cycle, seasonal, and diurnal variations of subauroral ion drifts: Statistical results

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