The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth's Magnetic Field

When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth's polar cap region, but such an effect has not been previously observed because the energies of...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2020-04, Vol.125 (4), p.n/a
Main Authors: Li, Kun, Förster, Matthias, Rong, Zhaojin, Haaland, Stein, Kronberg, Elena, Cui, Jun, Chai, Lihui, Wei, Yong
Format: Article
Language:English
Subjects:
Atmosphere
Atmospheric evolution
Charged particles
Dipoles
Earth
Earth's magnetic field
Electron precipitation
Energy sources
Geomagnetic field
Geomagnetism
Inhomogeneity
Ionosphere
Ions
Magnetic fields
Magnetism
Mars
Mars magnetic field
Outflow
Planetary magnetic fields
Polar caps
Polar environments
Polar regions
Polar wind
Solar activity
Solar magnetic field
Spacecraft
Strength
Venus
Venus atmosphere
Venus magnetic field
Wind
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Summary:When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth's polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the low‐energy ions with a positively charged spacecraft. In this study, we found an anticorrelation between ionospheric outflow and the strength of the Earth's magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth's magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels. Plain Language Summary Earth, Venus, and Mars have very different atmospheres although they are thought to possess similar atmospheres about 4.5 billion years ago. One of the main reasons considered for the losses of H2O and O2 is dramatic decreases in the dipole magnetic field on Venus and Mars. Although the Earth has kept its intrinsic magnetic field, there are variations in both orientation and strength. Previous observations have confirmed that atmospheric loss is controlled by the orientation of the geomagnetic dipole. However, the effect of variations in the strength of the Earth's magnetic field on atmospheric outflow has not been addressed. In this study, we have focused on the polar wind, the dominant ionospheric outflow from the polar regions. Our results reveal an anticorrelation between the outflow and the strength of the Earth's magnetic field, offering us a clue on the ionospheric and atmospheric evolution with a changing magnetic field. Key Points The density and the particle flux of the polar wind are revealed to be anticorrelated with the strength of the Earth's magnetic field The polar rain can be the main energy source of the polar wind in the southern hemisphere during periods of high solar activity levels A strong magnetic field diminishes energy depositions in the polar cap and thus controls the density and particle flux of the polar wind
ISSN:2169-9380
2169-9402
DOI:10.1029/2020JA027802