Features of the polar cap aurorae in the southern polar region

Трошичев, О. А.; Gusev, M.G.; Nickolashkin, S.V.; Самсонов, В. П.

doi:10.1016/0032-0633(88)90102-x

Cited by 38 publications

(17 citation statements)

References 23 publications

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“…In the study of Kullen et al (2002), the highest probability of having northward IMF was found 1 to 2 h before polar cap arc detection. The delay between a northward turning of the IMF and the appearance of polar cap arcs has been estimated to be 1 h (Troshichev et al, 1988). On the other hand, the estimated delay between a southward turning of the IMF and the disappearance of polar cap arcs varies from 10-15 min (Troshichev et al, 1988) to 30 min (Valladares et al, 1994;Rodriguez et al, 1997).…”

Section: Pcib Dependence On Imf B Zmentioning

confidence: 99%

Polar cap ion beams during periods of northward IMF: Cluster statistical results

et al. 2011

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Abstract. Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static fieldaligned electric field that can extend to altitudes higher than 7 R E (Maggiolo et al., 2006;Teste et al., 2007).Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 R E and in the Northern Hemisphere.We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ∼40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component.The analysis of the variation of the IMF B Z component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ∼2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the impliCorrespondence to: R. Maggiolo (romain.maggiolo@aeronomie.be) cations of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF.

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Section: Pcib Dependence On Imf B Zmentioning

confidence: 99%

Polar cap ion beams during periods of northward IMF: Cluster statistical results

et al. 2011

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“…There is also clear evidence that they occur during quiet geomagnetic periods, with some delay after a northward turning of the IMF -estimated to about 1 h by Troshichev et al (1988). However, about 20 % (Valladares et al, 1994) to 30 % (Rairden and Mende, 1989) of them are observed when the IMF B Z is southward oriented suggesting that there is a delay between a southward turning of the IMF and the disappearance of polar cap arcs.…”

Section: Introductionmentioning

confidence: 97%

“…However, about 20 % (Valladares et al, 1994) to 30 % (Rairden and Mende, 1989) of them are observed when the IMF B Z is southward oriented suggesting that there is a delay between a southward turning of the IMF and the disappearance of polar cap arcs. Such a delay has been estimated from ground-based optical observations and it varies from 10-15 min (Troshichev et al, 1988) to 30 min (Valladares et al, 1994;Rodriguez et al, 1997). The influence of IMF B Y and B X on the PCA dynamics is even less understood.…”

Section: Introductionmentioning

confidence: 99%

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

et al. 2012

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Abstract. On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasistationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV.The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data.We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi-static acceleration of electrons that generate a polar cap arc as they precipitate in the ionosphere. The detailed observations of the acceleration region by Cluster and the large scale image of the polar cap arc provided by TIMED are two different features of the same phenomenon. Combined together, they bring new light on the configuration of the high-latitude magnetosphere during prolonged periods of Northward IMF. Possible implications of the modelling results for optical observations of polar cap arcs are also discussed.

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“…Since many polar arcs are sun-aligned, an all-sky camera positioned within the polar cap preferentially detects arcs in its noon and midnight sectors; Only very bright arcs are detected in its dawn and dusk sectors. This may explain some inconsistencies between previously reported statistical distributions of polar arcs at the south pole (Troshichev et al, 1988) and satellite imagery of the theta aurora (Frank et al, 1986). Bearing in mind that the observations presented here suffer from similar deficiencies, this study puts special emphasis on trying to avoid the subtle implications of detection threshold effects on data interpretation.…”

Section: A February 17 1993 Case Studymentioning

confidence: 73%

“…These observations imply that weak, diffuse optical emissions might be observed over a large region from the auroral oval up to the polar arcs. Indeed, Troshichev et al (1988) reported on the observation of discrete arcs above the south pole that were immersed in a wide band of diffuse luminescence for 3 continuous hours. However, this was a single event for 5 years worth of data, which makes the phenomenon unique.…”

Section: Introductionmentioning

confidence: 99%

Auroral Emissions at the North Magnetic Pole-A February 17, 1993 Case Study.

Oznovich

McEwen

1994

J. geomagn. geoelec

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During the first 12 1/2 hours of February 17, 1993, 21 apparently-isolated events of discrete polar arcs were recorded in broad-band visual light by an all-sky camera and in the blue, green, and red lines by a meridian scanning photometer at Eureka, an observatory near the north magnetic pole (89° magnetic latitude). The polar arcs were located almost exclusively in the dusk sector. Most of the arcs (>60%) were faint (s1 kR in the blue, green, or red lines). The remainder were bright arcs (1-17 kR in the green) associated with energy fluxes of 1-7 erg cm-2s_1 and characteristic energies of -0.6 keV. The average lifetime of an individual polar arc was 8 minutes. One of the 21 identified events of polar arcs was associated with diffuse emissions duskward of the arc. The faint (0.5 kR in the green) diffuse emissions extended from the dusk horizon of the camera up to the arc. They were associated with very soft (Eo < 0.4 keV) and low flux (0.2 erg cm-29-1) particle precipitation. These emissions were probably the optical manifestation of particle entry phenomena reported in the past, namely the location of transpolar arcs at the poleward edge of continuous soft particle precipitation. The lifetime of the diffuse emission (40 min) was much longer than the lifetime of the polar arc (6 min) and it did not follow the duskward motion of the arc. We show a time sequence of a new phenomenon regarding sun-aligned arcs-short lived, antisunward propagating intensifications in the form of bright spots spread over a very small spatial scale along the arc.

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Features of the polar cap aurorae in the southern polar region

Cited by 38 publications

References 23 publications

Polar cap ion beams during periods of northward IMF: Cluster statistical results

Polar cap ion beams during periods of northward IMF: Cluster statistical results

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

Auroral Emissions at the North Magnetic Pole-A February 17, 1993 Case Study.

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