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

Maes, Lukas; Maggiolo, Romain; Keyser, Johan De

doi:10.5194/angeo-34-961-2016

Cited by 5 publications

(5 citation statements)

References 69 publications

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“…Despite all the statistical issues with uneven sampling and the bias in F 10.7 , we do also find a seasonal trend in the southern hemisphere, and a less convincing trend in the northern hemisphere, as was predicted by, for example, Maes et al (). This is further evidence for the impact of solar illumination on the ion outflow via modulation of the ionosphere.…”

Section: Discussionsupporting

confidence: 69%

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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Section: Discussionsupporting

confidence: 69%

Solar Illumination Control of the Polar Wind

et al. 2017

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“…Horizontal axes show season; vertical axes show the fraction of polar cap area illuminated assuming a terminator at 90° solar zenith angle. [after Maes et al , ].…”

Section: Discussion and Summarymentioning

confidence: 98%

“…Since, at least on average, the total amount of magnetic flux in the Northern and Southern Hemispheres must be equal, the polar cap area (defined by open magnetic field lines) and thus source area for ion outflow will thus be different between the Northern and Southern Hemispheres (Figure 5b). Likewise, the larger offset between the magnetic and geographic poles in the Southern Hemisphere leads to larger diurnal variations in solar illumination in the Southern Hemisphere [e.g., see Barakat et al, 2015;Maes et al, 2016] (Figure 5c).…”

Section: Discussion and Summarymentioning

confidence: 99%

North‐south asymmetries in cold plasma density in the magnetotail lobes: Cluster observations

et al. 2017

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In this paper, we present observations of cold (0–70 eV) plasma density in the magnetotail lobes. The observations and results are based on 16 years of Cluster observation of spacecraft potential measurements converted into local plasma densities. Measurements from all four Cluster spacecraft have been used, and the survey indicates a persistent asymmetry in lobe density, with consistently higher cold plasma densities in the northern lobe. External influences, such as daily and seasonal variations in the Earth's tilt angle, can introduce temporary north‐south asymmetries through asymmetric ionization of the two hemispheres. Likewise, external drivers, such as the orientation of the interplanetary magnetic field can set up additional spatial asymmetries in outflow and lobe filling. The persistent asymmetry reported in this paper is also influenced by these external factors but is mainly caused by differences in magnetic field configuration in the Northern and Southern Hemisphere ionospheres.

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“…The upward flux (ions m −2 s −1 ) depends on solar illumination, which affects the properties of the ionosphere. The flux is small and steady compared to that in the cusps (Maes et al 2016), but the area of the polar cap is larger than that of the cusp by an order of magnitude. The escape rate scales with the area of the polar caps (defined in Appendix A.1).…”

Section: Escape Processesmentioning

confidence: 89%

Why an intrinsic magnetic field does not protect a planet against atmospheric escape

Gunell

Maggiolo

Nilsson

et al. 2018

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The presence or absence of a magnetic field determines the nature of how a planet interacts with the solar wind and what paths are available for atmospheric escape. Magnetospheres form both around magnetised planets, such as Earth, and unmagnetised planets, like Mars and Venus, but it has been suggested that magnetised planets are better protected against atmospheric loss. However, the observed mass escape rates from these three planets are similar (in the approximate (0.5−2) kg s −1 range), putting this latter hypothesis into question. Modelling the effects of a planetary magnetic field on the major atmospheric escape processes, we show that the escape rate can be higher for magnetised planets over a wide range of magnetisations due to escape of ions through the polar caps and cusps. Therefore, contrary to what has previously been believed, magnetisation is not a sufficient condition for protecting a planet from atmospheric loss. Estimates of the atmospheric escape rates from exoplanets must therefore address all escape processes and their dependence on the planet's magnetisation.

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

Cited by 5 publications

References 69 publications

Solar Illumination Control of the Polar Wind

Solar Illumination Control of the Polar Wind

North‐south asymmetries in cold plasma density in the magnetotail lobes: Cluster observations

Why an intrinsic magnetic field does not protect a planet against atmospheric escape

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