Rapid subauroral ion drifts observed by Atmosphere Explorer C

Spiro, R. W.; Heelis, R. A.; Hanson, W. B.

doi:10.1029/gl006i008p00657

Cited by 275 publications

(279 citation statements)

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“…This is in agreement with earlier findings, such as by Spiro et al (1979), Anderson et al (1991), Karlsson et al (1998), Burke et al (2000), Anderson et al (2001), and with the model predictions presented by Southwood and Wolf (1978). 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.…”

Section: Discussionsupporting

confidence: 92%

“…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%

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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: 92%

Section: Introductionmentioning

confidence: 99%

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

2004

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“…Another mesoscale ionospheric convection phenomena that has been studied by SuperDARN is that known variously as polarization jets (PJs) (Galperin et al 1973), or subauroral ion drifts (SAIDs) (Spiro et al 1979). These are fast (1-4 km/s), narrow (1-2 8) channels of westward plasma flow which occur near the equatorward edge of the auroral oval in the evening sector ionosphere.…”

Section: The Structure and Dynamics Of Mesoscale Convectionmentioning

confidence: 99%

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

et al. 2007

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The Super Dual Auroral Radar Network (SuperDARN) has been operating as an international co-operative organization for over 10 years. The network has now grown so that the fields of view of its 18 radars cover the majority of the northern and southern hemisphere polar ionospheres. SuperDARN has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere,

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“…Usually embedded within the SAPS are narrow (~1°) subauroral ion drifts [Spiro et al, 1979] or polarization jets [Galperin et al, 1974] with flow magnitude higher than 500 m s À1 [Spiro et al, 1979] or 1 km s À1 . The selection of the velocity threshold seems arbitrary.…”

Section: à2mentioning

confidence: 99%

On the generation/decay of the storm‐enhanced density plumes: Role of the convection flow and field‐aligned ion flow

et al. 2014

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Storm-enhanced density (SED) plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes. The generation and decay mechanisms of the plumes are still not clear. We present observations of SED plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes, including vertical ion flow, field-aligned ion flow and flux, plasma temperature, and field-aligned currents, obtained from multiple instruments, including GPS total electron content (TEC), Poker Flat Incoherent Scatter Radar (PFISR), Super Dual Auroral Radar Network, and Active Magnetosphere and Planetary Electrodynamics Response Experiment. The TEC increase within the SED plumes at the PFISR site can be 1.4-5.5 times their quiet time value. The plumes are usually associated with northwestward E × B flows ranging from a couple of hundred m s À1 to > 1 km s À1. Upward vertical flows due to the projection of these E × B drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement. The upward vertical flows near the poleward part of the plumes are more persistent, while those near the equatorward part are more patchy. In addition, the plumes can be collocated with either upward or downward field-aligned currents (FACs) but are usually observed equatorward of the peak of the Region 1 upward FAC, suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows. Furthermore, during the decay phase of the plume, large downward ion flows, as large as~200 m s À1, and downward fluxes, as large as 10 14 m À2 s À1, are often observed within the plumes. In our study of six storms, enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow/flux cases, but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude. For the latter two cases, enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line. These downward flows should be an important mechanism for the decay of the SED plumes. IntroductionDuring enhanced geomagnetic activity periods, in particular storms, significant electron density enhancements are often observed in the midlatitude and subauroral region, which are named storm-enhanced densities (SEDs) [Foster, 1993]. Often, SEDs extend northwestward to higher latitudes and form a plume. This plume can occasionally be entrained into the cusp region and then enter the polar cap, where it is termed the tongueof-ionization (TOI) or, if it is not continuous, a polar cap patch, depending on the shape and spatial coverage of the high-density region there [e.g., Foster et al., 2005;Moen et al., 2013]. The SED plume is suggested to be the ionospheric projection of a plasmaspheric plume in the magnetospheric equatorial plane . Within the magnetosphere, plasmaspheric plumes can play...

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Rapid subauroral ion drifts observed by Atmosphere Explorer C

Cited by 275 publications

References 5 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

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

On the generation/decay of the storm‐enhanced density plumes: Role of the convection flow and field‐aligned ion flow

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