A survey of the polar cap density based on Cluster EFW probe measurements: Solar wind and solar irradiation dependence

The plasma density above the Earth's polar caps provide crucial information about the state of the magnetosphere. This region of space is known for its tenuous plasma and extremely low plasma densities, thus making traditional measurements with particle and plasma instruments extremely difficul...

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Bibliographic Details
Published in:Journal of Geophysical Research: Space Physics 2012-01, Vol.117 (A1), p.n/a
Main Authors: Haaland, S., Svenes, K., Lybekk, B., Pedersen, A.
Format: Article
Language:English
Subjects:
Astronomy
Astrophysics
Atmospheric sciences
Dependence
Earth sciences
Earth, ocean, space
electron density
Exact sciences and technology
Ionization
Irradiation
Magnetic fields
Magnetism
Physics
Plasma
Plasma physics
polar cap
polar cap density
Space
Spacecraft
Sun
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Summary:The plasma density above the Earth's polar caps provide crucial information about the state of the magnetosphere. This region of space is known for its tenuous plasma and extremely low plasma densities, thus making traditional measurements with particle and plasma instruments extremely difficult. A new method based on spacecraft potential measurements from the electric field instrument onboard the Cluster satellites has shown that more reliable density measurements can be obtained. In this paper, we utilize this method and present a survey of the polar cap densities and the response to changes in the solar irradiation, solar wind parameters as well as processes internal to the magnetosphere. Our observations spans a time interval of almost 10 years, thus covering almost a full solar cycle. The observations seem to confirm that solar irradiance, and thus ionization through UV absorption in the atmosphere is the most important mechanism controlling the polar cap cold plasma density. We also find positive correlations between polar cap density and solar wind density and solar wind dynamic pressure, as well as geomagnetic activity levels. Key Points An extensive survey of polar cap cold plasma densities is presented The high‐altitude polar cap density is mainly controlled by solar irradiance Results suggest that ionospheric outflow is the dominant source of cold plasma
ISSN:0148-0227
2169-9380
2156-2202
2169-9402
DOI:10.1029/2011JA017250