Solar illumination control of ionospheric outflow above polar cap arcs

Maes, Lukas; Maggiolo, Romain; Keyser, Johan De; Dandouras, I.; Fear, R. C.; Fontaine, Dominique; Haaland, Stein

doi:10.1002/2014gl062972

Cited by 15 publications

(25 citation statements)

References 59 publications

(82 reference statements)

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“…This has been evidenced by many observational studies and models (Abe et al, 1993;Su et al, 1998a, b;Glocer et al, 2012;Maes et al, 2015). Maes et al (2015), studying outflow above smallscale polar cap arcs using Cluster (Escoubet et al, 2001) measurements, found that the upflow above the polar cap can be roughly divided into two distinct groups based on the solar zenith angle (SZA) of the footpoint of the field line in the ionosphere. The border between both was found to be around ∼ 100…”

Section: Introductionmentioning

confidence: 89%

“…Since precipitating electrons caused by the polar cap arc system deposit energy in the ionosphere below, this might cause concern that these flux densities are not representative of the polar wind. Maes et al (2015) argued to the contrary, since they found that the magnitude of the relatively small potential drop of the polar cap arcs (and thus the energy of the precipitating electrons) does not seem to have any discernable effect on the flux densities. The fact that the outflow is predominantly controlled by the ionospheric illumination conditions also indicates that the energy deposited in the ionosphere by precipitation in polar cap arcs plays a minor role.…”

Section: Methodsmentioning

confidence: 99%

“…Inspired by the two regimes in upflowing ion fluxes above a sunlit and a dark ionosphere found by Maes et al (2015), as discussed in the introduction, we assume that there are only two possible flux density values (ions m −2 s −1 ): one above a sunlit ionosphere and one above a dark ionosphere. Thus, we ignore all other factors that may have an influence on the outflow and cause a large natural spread, like variations in irradiance, flows, and density fluctuations in the neutral upper atmosphere, geomagnetic activity, etc.…”

Section: Methodsmentioning

confidence: 99%

“…We take their values from the study in Maes et al (2015) as the average value for upflow below SZA of 100…”

Section: Methodsmentioning

confidence: 99%

“…It is thus the variation in the sunlit fraction of the polar caps that introduces a time dependence into the total flux (as well as the size of the total polar cap in the third case, as explained further on). Note that these flux densities from Maes et al (2015) actually come from measurements of ion outflow above polar cap arcs. Since precipitating electrons caused by the polar cap arc system deposit energy in the ionosphere below, this might cause concern that these flux densities are not representative of the polar wind.…”

Section: Methodsmentioning

confidence: 99%

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Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

2016

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Abstract. The cold ions (energy less than several tens of electronvolts) flowing out from the polar ionosphere, called the polar wind, are an important source of plasma for the magnetosphere. The main source of energy driving the polar wind is solar illumination, which therefore has a large influence on the outflow. Observations have shown that solar illumination creates roughly two distinct regimes where the outflow from a sunlit ionosphere is higher than that from a dark one. The transition between both regimes is at a solar zenith angle larger than 90 • . The rotation of the Earth and its orbit around the Sun causes the magnetic polar cap to move into and out of the sunlight. In this paper we use a simple set-up to study qualitatively the effects of these variations in solar illumination of the polar cap on the ion flux from the whole polar cap. We find that this flux exhibits diurnal and seasonal variations even when combining the flux from both hemispheres. In addition there are asymmetries between the outflows from the Northern Hemisphere and the Southern Hemisphere.

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Section: Introductionmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…We take their values from the study in Maes et al (2015) as the average value for upflow below SZA of 100…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

2016

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A statistical study of magnetospheric ion composition along the geomagnetic field using the Cluster spacecraft forLvalues between 5.9 and 9.5

et al. 2016

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Using ion density data obtained by the CODIF (ion Composition and Distribution Function analyser) instrument on board the Cluster spacecraft, for the interval spanning 2001–2005, an empirical model describing the average ion mass distribution along closed geomagnetic field lines is determined. The empirical model describes the region spanning 5.9≤L < 9.5, with dependences on L shell and magnetic local time included, and represents ions in the energy range of 0.025 to 40 keV/charge. The data reduction process involves the identification and rejection of CODIF data contaminated by penetrating energetic radiation belt particles, found to frequently occur for L < 5.9. Furthermore, a comparison of data with observations of the cold plasma population in the region provides evidence that the CODIF data set is representative of the full plasma population. The variations in average ion mass along the field lines were modeled using a power law form, which maximizes toward the magnetic equatorial plane, with observed power law index values ranging between approximately −2.0 and 0.0. The resulting model illustrates some key features of the average ion mass spatial distribution, such as an average ion mass enhancement at low L in the evening sector, indicating the transport of high‐latitude heavy ion outflows to the closed inner magnetosphere.

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Solar Illumination Control of the Polar Wind

et al. 2017

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Polar wind outflow is an important process through which the ionosphere supplies plasma to the magnetosphere. The main source of energy driving the polar wind is solar illumination of the ionosphere. As a result, many studies have found a relation between polar wind flux densities and solar EUV intensity, but less is known about their relation to the solar zenith angle at the ionospheric origin, certainly at higher altitudes. The low energy of the outflowing particles and spacecraft charging means it is very difficult to measure the polar wind at high altitudes. We take advantage of an alternative method that allows estimations of the polar wind flux densities far in the lobes. We analyze measurements made by the Cluster spacecraft at altitudes from 4 up to 20 RE. We observe a strong dependence on the solar zenith angle in the ion flux density and see that both the ion velocity and density exhibit a solar zenith angle dependence as well. We also find a seasonal variation of the flux density.

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Solar illumination control of ionospheric outflow above polar cap arcs

Cited by 15 publications

References 59 publications

Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

A statistical study of magnetospheric ion composition along the geomagnetic field using the Cluster spacecraft forLvalues between 5.9 and 9.5

Solar Illumination Control of the Polar Wind

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