Open AccessA survey of the polar cap density based on Cluster EFW probe measurements: Solar wind and solar irradiation dependence
Author(s) -
Haaland S.,
Svenes K.,
Lybekk B.,
Pedersen A.
Publication year - 2012
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011ja017250
Subject(s) - polar wind , solar wind , solar irradiance , magnetosphere , physics , plasma , polar , atmospheric sciences , earth's magnetic field , magnetosphere of jupiter , ionization , computational physics , interplanetary magnetic field , astronomy , magnetic field , ion , quantum mechanics
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.